The Ultimate Guide for Laser and IPL in the Aesthetic Field [1st ed. 2023] 3031276310, 9783031276316

Table of contents :
Acknowledgment
Contents
Chapter 1: Skin, Light, and Their Interactions
Skin Anatomy
Epidermis (EP)
Stratum Corneum
Stratum Grаnulоѕum
Stratum Sріnоѕum
Stratum Basale
Melanocytes
Dermis
Subcutaneous Layer
Histology of Normal Skin
Changes due to Intrinsic Aging
Changes due to Photoaging
Epidermis (EP)
Dermis
Classification of Photoaging
Light-Based Treatment
Light-Tissue Interaction
Skin’s Chromophores
Selective Photothermolysis
Chemical Photosensitization
Photoacoustic Effect
Light Parameters
Wаvеlеngthѕ (nm)
Fluence (J/cm2)
Pulse Widths (Fraction of a Second)
Train of Sequential Sub-pulses
Pulse Shape
Spot Size (mm)
Depth of Penetration
Repetition Rate (Hz) for the Device
Skin Histology Changes After Laser Interaction
Laser Hair Removal
Skin Rejuvenation with Color-Sensitive Laser
Non-ablative Color-Blind Laser
Picosecond
CO2 Fractional
Er:YAG Fully Ablative
Skin Lesion Characteristics
Absorption and Contrast
Skin Phototypes
Fitzpatrick Assessment
Skin Reflectance Colorimeter
Thermal Relaxation Time (TRT) and Size
Depth of the Lesion
References
Chapter 2: Laser and Intense Pulsed Light
IPL
Types of IPLS
IPL with Interchangeable Filters
Comparison
IPL with Interchangeable Handpieces (Applicators)
Comparison
Special IPL
Lasers
Color Sensitive
Color-Blind
Color Sensitive According to Pulse Width
Long Millisecond (ms) and Quasi-long Microsecond (μs) Laser
532 nm KTP
Comparison
excel V Interface
585 and 595 nm Pulsed Dye Lasers (PDL)
Comparison
Vbeam Interface
755 nm Alexandrite (Alex) Laser
Comparison
GentleMax
Diode Laser
High-Fluence Static Mode
LightSheer
HS Vacuum Handpiece
ET Standard Handpiece
Vectus Cynosure
Low-Fluence Dynamic Super Hair Removal (SHR)
Comparison
1064 nm ND:YAG Laser
Comparison
GentleMax
Short Q-Switched Nanosecond (ns) Laser
532 nm KTP
585 and 595 nm Pulsed Dye Lasers (PDL)
1064 nm ND:YAG Laser
Comparison
Lutronic Spectra Interface
Ultrashort Picosecond (ps) Laser
Comparison
Color-Blind Lasers
Resurfacing Lasers
Fractional Non-ablative Lasers (FNAL)
Comparison
Halo Laser
Fractional Ablative Lasers (FAL)
What Is Stacking
2940 ER:YAG and CR:YSGG 2790 nm Laser
Comparison
Fotona Dynamis
iPixel ER:YAG 2940 nm 2 Hz Applicator; 7 × 1 iPixel Roller
10,600 nm CO2 Laser
Indications
Comparison
eCO2 by Lutronic
CO2RE by Candela
ULT Rapulse by Lumenis (Fig. 2.32, Table 2.25)
References
Chapter 3: Hair Removal
Hair Follicles
Anatomy
Growth
Assessment
Hair Color
Texture and Coarseness
Glove Test
Hair Density
Extremities and Face
Abdomen
Pubic Region
Skin Phototype
Fitzpatrick Assessment
Skin Reflectance Colorimeter
Wavelength
Available Technology
IPL
IPL Equipped with a Single Filter
IPL-SQ from Vydence
Lumenis M22 IPL
Forever BARE by BBL Sciton
IPL Equipped with Different Applicators
Icon Palomar by Cynosure
IPL Equipped with a Dual Filter
Nordlys Ellipse by Candela
Harmony by Alma
elos Pulse with Motif HR Applicator
Choosing IPL for Your Practice
Pre-treatment Instruction
Medical History
Managing Clients’ Expectations
Possible Side Effects and Adverse Reactions
Procedure
Endpoint
Post-treatment Instruction
Long-Pulsed Alexandrite 755 nm
Pre-treatment Instruction
Procedure
Parameters
Endpoint
Long-Pulsed Diode 810 nm
High-Fluence Single Pass
Endpoint
Low Fluence with Multiple Passes
Endpoint
Long-Pulsed ND:YAG 1064 nm
Procedure
Parameters (Tables 3.15 and 3.16)
Endpoint
Blended Blend Wavelengths
Electro-optical Synergy
How to Choose a System for Hair Removal
References
Chapter 4: Acne Vulguris
Active Acne Vulgaris
Acne Assessment
Subjective Tools and Questioners
Objective Tools and Skin Analyzers
Treatment Options
Light-Based Treatment
Mechanism of Action
IPL
Wavelengths to Be Used
The Pulse Time
The Correct Energy
Single Cutoff Filter
Icon Palomar by Cynosure
Fluence and Pulse Width
Negative Pneumatic Pressure IPL
A Dual-Filter IPL
Nordlys by Candela
Harmony by Alma
M22 Form Lumenis
Comparison of Dual-Filter IPL for Acne
532 nm KTP Laser
585 and 595 nm Pulsed Dye Laser
Long-Pulsed PDL
Short Pulse Duration
1064 Nd:YAG Laser
Long and Quasi-long Pulse Width in Millisecond
Short-Pulsed Laser
Non-ablative Fractional Lasers
1450 nm Diode Laser
1540 and 1550 nm ER: Glass Laser
Fraxel Dual from Solta
Icon 1540 Fractional Laser from Cynosure
Alma Harmony XL Pro ClearSkin Pro Er:Glass 1540 nm
Frax Pro® 1550 from Candela
Choosing a Device for Acne Treatment
References
Chapter 5: Hyperpigmentation
Epidermal Pigmented Lesions: Actinic Lentigines and Ephelides
IPL
Pre-treatment Instructions
Other Pre- and Post-treatment Options
An Accurate Medical History
Test Spot
Treatment
Treatment Parameters
Vydence IPL-Sq
Lumenis M22® IPL
Harmony
Icon®
MaxY®
MaxG®
Post-treatment Care
Laser
Color-Sensitive Lasers
Long-Pulsed Lasers
Pulsed Dye Laser
Alex 755
Q-Switched Short-Pulsed Lasers
Melasma
Assessment
Managing Patient Expectation
Etiology
Classification
Treatment
Topical Agents
Active Ingredients and Mechanism of Actions
Indication
Light-Based Treatments
IPL
Lumenis M22®
Lumecca from InMode
Nordlys Ellipse by Candela
Cooling
The Treatment Parameter
Clinical Endpoint
Q-Switched Nanosecond Lasers
Endpoint
Treatment Parameters
Combination with Tranexamic Acid
Picosecond Lasers
Fractional Non-ablative Laser (FNAL)
Water as a Chromophore
Wavelength
1550 nm
Test Spot
Pain Level and Redness
1927 nm
Combination
Test Spot
Pain Level
Ablative Fractionated Resurfacing Lasers
Conclusion
References
Chapter 6: Scar Revision
Scar Assessment and Types
Atrophic Scars
Light-Based Treatment
Intense Pulse Light
Color-Sensitive Lasers
Long Pulse
Short-Pulsed Q-Switched Nanosecond Lasers
Ultrashort
Histological Changes
Color-Blind Lasers
Non-ablative Fractional Laser (FNAL)
Histology Changes
Clinical Endpoint
Test Spot
Post-treatment
Fraxel Dual
Icon® 1540 Fractional Laser
ClearSkin Pro
Ablative Fractional Laser
CO2
Histological Changes
ER:YAG
Histological Changes
Summary of Suggested Treatments
Hypertrophic Scars and Keloids
Etiology
Light-Based Treatment
Intense Pulse Light
Color-Sensitive Lasers
Long-Pulsed Lasers
Quasi-long-Pulsed Nd:YAG 1064 nm (Millisecond Range)
Q-Switched Nanosecond Laser
Ultrashort Picosecond Lasers
Color-Blind Lasers
Non-ablative Fractional Laser
Ablative Fractional Laser
CO2 Laser
Indications
Comparison
eCO2 by Lutronic
CO2RE by Candela
UltraPulse by Lumenis (Fig. 6.18; Table 6.21)
ER:YAG
Stacking
References
Chapter 7: Stretch Marks (Striae Distensae)
Etiology
Light Base Treatment
IPL
Pulsed Dye Laser
1064 nm ND:YAG
Fractional Non-ablative Lasers
1540 Fractional Laser
1550 nm Er:Glass Laser
1565 nm Laser
Fractional Ablative Lasers
10,064 nm CO2 Laser
Fractional Er:YAG Laser
References
Chapter 8: Laser Vaginal Rejuvenation
Laser Vaginal Rejuvenation
Fractional CO2
Non-ablative Er:YAG
Hybrid Fractional Laser
Treatment Procedures
Evaluation, Consultation, and Follow-Up
Consultation/Education
Medical History
Informed Consent
Medication
Follow-Up
Possible Side Effects
Contraindications
References
Chapter 9: Buying a New Laser or IPL Devices
Stand-Alone Versus Modular Platforms
Planning Your Next Device Purchase
Refurbished Devices
References
Chapter 10: Buying a Refurbished Laser Device
Medical Device Regulations in the United States
Marketing or Selling a New Medical Device
Device Classifications
FDA Medical Device Approval Pathways
Marketing or Selling a Refurbished Medical Device
FDA Control of Refurbished Device Trading in the United States
Obligation in Terms of Reservicing a Medical Device
Problem with Buying Refurbished Laser Device
References
Appendix
General Laser Consent Form
General Post-Care
What to Expect After Treatment
What You May Feel and Look Like
How to Care for Your Skin After Treatment
Laser Hair Removal
Consent Form
Pre- and Post-Care
Pre-Care
Post-Care
Non-ablative Fractional Laser
Consent Form
Pre- and Post-Care
Pre-Care
Post-Care 1
What to Expect Following Treatment
What You May Feel and Appear to Be
How to Take Care of Your Skin Following Treatment
Post-Care 2
Following Treatment
Rosacea and Spider Vein Removal
Consent Form
Post-Treatment Instructions
CO2 Laser
Pre- and Post-Care
Pre-Care
Post-Care
Acne Treatments
Consent Form 1
Consent Form 2
A Review of Light Therapy Facts
Common Risks and Side Effects
Pre- and Post-Care
Pre-Care
Post-Care
Melasma
Pre- and Post-Care
Pre-Care
Post-Care
Index

Citation preview

The Ultimate Guide for Laser and IPL in the Aesthetic Field Kamal Alhallak Adel Abdulhafid Salem Tomi Dima Omran

123

The Ultimate Guide for Laser and IPL in the Aesthetic Field

Kamal Alhallak • Adel Abdulhafid  Salem Tomi • Dima Omran

The Ultimate Guide for Laser and IPL in the Aesthetic Field

Kamal Alhallak Albany Cosmetic and Laser Center Edmonton, AB, Canada

Adel Abdulhafid University of Alberta Edmonton, AB, Canada

Salem Tomi Albany Cosmetic and Laser Center Edmonton, AB, Canada

Dima Omran Albany Cosmetic and Laser Center Edmonton, AB, Canada

ISBN 978-3-031-27631-6    ISBN 978-3-031-27632-3 (eBook) https://doi.org/10.1007/978-3-031-27632-3 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland

This book is dedicated to two of the most influential people in my life: my mother, Daad Shiekho, and my wife, Dima Omran, who is also a co-author. I’d also like to dedicate this book to my late father, Nizar Alhallak, may his soul rest in peace. Finally, this book is dedicated to Nizar Junior and Mohammad, my children. Kamal Alhallak

Acknowledgment

I thank all the medical professionals and laser technicians at the Albany Cosmetic and Laser Center, especially Darian Holtby. Moreover, I wish to extend my gratitude to Dr. Shirzad Azarmi’s unwavering assistance throughout my Ph.D. lab work at the University of Alberta. Special acknowledgment and heartful thanks to my Ph.D.  Supervisor Dr. Raimar Leobenberg and my supervisory committee, Dr. Wilson Roa, Dr. Warren Finlay, and Dr. Ayman Elkadi. Finally, I wish to thank Drs. Amir Mardini, George Laham, and Anton Laham for their unwavering assistance during my time at Damascus University. Kamal Alhallak

vii

Contents

1

 kin, Light, and Their Interactions��������������������������������������������������������    1 S Skin Anatomy��������������������������������������������������������������������������������������������    1 Epidermis (EP)��������������������������������������������������������������������������������������    1 Dermis����������������������������������������������������������������������������������������������������    5 Subcutaneous Layer ������������������������������������������������������������������������������    6 Histology of Normal Skin��������������������������������������������������������������������������    6 Changes due to Intrinsic Aging������������������������������������������������������������������    7 Changes due to Photoaging������������������������������������������������������������������������    7 Epidermis (EP)��������������������������������������������������������������������������������������    7 Dermis����������������������������������������������������������������������������������������������������    7 Classification of Photoaging������������������������������������������������������������������    9 Light-Based Treatment������������������������������������������������������������������������������   10 Light-Tissue Interaction����������������������������������������������������������������������������   10 Skin’s Chromophores����������������������������������������������������������������������������   11 Light Parameters������������������������������������������������������������������������������������   13 Skin Histology Changes After Laser Interaction ����������������������������������   25 Skin Lesion Characteristics��������������������������������������������������������������������   28 References��������������������������������������������������������������������������������������������������   36

2

 aser and Intense Pulsed Light��������������������������������������������������������������   39 L IPL��������������������������������������������������������������������������������������������������������������   40 Types of IPLS����������������������������������������������������������������������������������������   42 Lasers ��������������������������������������������������������������������������������������������������������   54 Color Sensitive��������������������������������������������������������������������������������������   54 Color-Blind��������������������������������������������������������������������������������������������   55 Color Sensitive According to Pulse Width��������������������������������������������   58 Color-Blind Lasers��������������������������������������������������������������������������������   78 References��������������������������������������������������������������������������������������������������   96

3

Hair Removal�������������������������������������������������������������������������������������������  101 Hair Follicles����������������������������������������������������������������������������������������������  103 Anatomy������������������������������������������������������������������������������������������������  103 ix

x

Contents

Growth ��������������������������������������������������������������������������������������������������  104 Assessment��������������������������������������������������������������������������������������������  106 Wavelength������������������������������������������������������������������������������������������������  109 Available Technology��������������������������������������������������������������������������������  109 IPL����������������������������������������������������������������������������������������������������������  109 Long-Pulsed Alexandrite 755 nm����������������������������������������������������������  131 Long-Pulsed Diode 810 nm ������������������������������������������������������������������  137 Long-Pulsed ND:YAG 1064 nm������������������������������������������������������������  142 Blended Blend Wavelengths������������������������������������������������������������������  146 Electro-optical Synergy�������������������������������������������������������������������������  147 How to Choose a System for Hair Removal����������������������������������������������  148 References��������������������������������������������������������������������������������������������������  148 4

Acne Vulguris�������������������������������������������������������������������������������������������  153 Active Acne Vulgaris����������������������������������������������������������������������������������  153 Acne Assessment ��������������������������������������������������������������������������������������  155 Subjective Tools and Questioners����������������������������������������������������������  155 Objective Tools and Skin Analyzers������������������������������������������������������  155 Treatment Options��������������������������������������������������������������������������������������  156 Light-Based Treatment��������������������������������������������������������������������������  157 Comparison of Dual-Filter IPL for Acne ����������������������������������������������  165 Choosing a Device for Acne Treatment ����������������������������������������������������  176 References��������������������������������������������������������������������������������������������������  177

5

Hyperpigmentation����������������������������������������������������������������������������������  181 Epidermal Pigmented Lesions: Actinic Lentigines and Ephelides ��������������������������������������������������������������������������������������������  182 IPL����������������������������������������������������������������������������������������������������������  183 Laser������������������������������������������������������������������������������������������������������  193 Melasma����������������������������������������������������������������������������������������������������  197 Assessment��������������������������������������������������������������������������������������������  197 Managing Patient Expectation ��������������������������������������������������������������  198 Etiology��������������������������������������������������������������������������������������������������  198 Classification������������������������������������������������������������������������������������������  199 Treatment ����������������������������������������������������������������������������������������������  199 Conclusion ������������������������������������������������������������������������������������������������  222 References��������������������������������������������������������������������������������������������������  222

6

Scar Revision��������������������������������������������������������������������������������������������  225 Scar Assessment and Types������������������������������������������������������������������������  225 Atrophic Scars��������������������������������������������������������������������������������������������  226 Light-Based Treatment��������������������������������������������������������������������������  228 Summary of Suggested Treatments ������������������������������������������������������  243 Hypertrophic Scars and Keloids����������������������������������������������������������������  243 Etiology��������������������������������������������������������������������������������������������������  246

Contents

xi

Light-Based Treatment��������������������������������������������������������������������������  246 Ultrashort Picosecond Lasers����������������������������������������������������������������  250 References��������������������������������������������������������������������������������������������������  261 7

 tretch Marks (Striae Distensae)������������������������������������������������������������  265 S Etiology������������������������������������������������������������������������������������������������������  265 Light Base Treatment��������������������������������������������������������������������������������  266 IPL����������������������������������������������������������������������������������������������������������  266 Pulsed Dye Laser ����������������������������������������������������������������������������������  267 1064 nm ND:YAG���������������������������������������������������������������������������������  267 Fractional Non-ablative Lasers��������������������������������������������������������������  268 Fractional Ablative Lasers ��������������������������������������������������������������������  270 References��������������������������������������������������������������������������������������������������  271

8

Laser Vaginal Rejuvenation��������������������������������������������������������������������  273 Laser Vaginal Rejuvenation ����������������������������������������������������������������������  274 Fractional CO2����������������������������������������������������������������������������������������  275 Non-ablative Er:YAG����������������������������������������������������������������������������  276 Hybrid Fractional Laser ������������������������������������������������������������������������  277 Treatment Procedures��������������������������������������������������������������������������������  279 Evaluation, Consultation, and Follow-Up��������������������������������������������������  280 Consultation/Education��������������������������������������������������������������������������  280 Medical History ������������������������������������������������������������������������������������  280 Informed Consent����������������������������������������������������������������������������������  280 Medication ��������������������������������������������������������������������������������������������  280 Follow-Up����������������������������������������������������������������������������������������������  281 Possible Side Effects������������������������������������������������������������������������������  281 Contraindications ��������������������������������������������������������������������������������������  281 References��������������������������������������������������������������������������������������������������  282

9

 uying a New Laser or IPL Devices������������������������������������������������������  285 B Stand-Alone Versus Modular Platforms����������������������������������������������������  286 Planning Your Next Device Purchase��������������������������������������������������������  287 Refurbished Devices����������������������������������������������������������������������������������  298 References��������������������������������������������������������������������������������������������������  300

10 B  uying a Refurbished Laser Device ������������������������������������������������������  301 Medical Device Regulations in the United States��������������������������������������  302 Marketing or Selling a New Medical Device����������������������������������������  302 Marketing or Selling a Refurbished Medical Device����������������������������  304 References��������������������������������������������������������������������������������������������������  307 Appendix ����������������������������������������������������������������������������������������������������������  309 Laser Hair Removal����������������������������������������������������������������������������������������  317

xii

Contents

Non-ablative Fractional Laser������������������������������������������������������������������������  321 Rosacea and Spider Vein Removal ����������������������������������������������������������������  329 Acne Treatments����������������������������������������������������������������������������������������������  335 Melasma������������������������������������������������������������������������������������������������������������  341 Index�������������������������������������������������������������������������������������������������������������������  343

Chapter 1

Skin, Light, and Their Interactions

Skin Anatomy The epidermis, dermis, and subcutaneous layers are the three major layers of human skin [1], listed from most superficial to deepest. Figure 1.1 depicts the various layers of normal skin, each containing a hair follicle. Each of the three skin layers contains the following sublayers of living and nonliving skin cells.

Epidermis (EP) The epidermis (EP), the skin’s outermost layer, is responsible for essential cosmetic qualities such as appearance and texture [2]. The thickness of the facial epidermis is 0.1 mm on average, with four sub-layers: stratum corneum (SC), stratum granulosum (SG), stratum spinosum, and stratum basale (SB) [3]. The epidermis must be renewed for the layers to function properly and for the skin to look appealing. The epidermis renewal cycle in the healthy skin lasts about 1 month, the time it takes for living keratinocytes from the basale to desquamate and migrate to the skin’s surface [4]. Stratum Corneum It comprises approximately 15 layers of nonliving keratinocytes (corneocytes) coated with a phospholipid film layer and linked by corneodesmosomes, as shown in the figure below. This layer serves as a physical barrier to pathogens and UV

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 K. Alhallak et al., The Ultimate Guide for Laser and IPL in the Aesthetic Field, https://doi.org/10.1007/978-3-031-27632-3_1

1

2

1  Skin, Light, and Their Interactions

Fig. 1.1  Different layers of the human skin, including a hair follicle

light. Furthermore, it regulates water loss through evaporation and keeps the skin hydrated [5]. The stratum corneum is typically 10–40 μm thick. The remaining epidermis layers are formed due to keratinocyte differentiation stages caused by migration and desquamation. This layer contains the least amount of water of any of the skin layers [6, 7]. Stratum Grаnulоѕum This is also known as the granular layer, and it is composed primarily of striated squamous сеllѕ arranged in 1–3 rows of lamellar granules [8]. It is important to note that beneath the раlmѕ and ѕоlеѕ, the skin lacks a well-defined ѕtrаtum lucidum and

Skin Anatomy

3

Fig. 1.2  Structure of SC and SG layers

stratum granulosum [9]. Figure  1.2 illustrates the structure of the stratum corneum layer. Stratum Sріnоѕum Also known as the spinous layer, it consists primarily of a cuboid cell arranged in multiple layers and synthesizes keratins that function to support structures. The сеllѕ are held together by specialized сеllѕ known as а dеѕmоѕоmеѕ [10]. Stratum Basale This іѕ the dеереѕt lауеr of thе eріdеrmіѕ, and it is alѕо known аѕ thе bаѕаl сеllѕ lауеr. The lауеr consists of tall columnar сеllѕ thаt are constantly undergoing cellular division and help form new kеrаtіnосуtеѕ (kеrаtіnіzаtіоn) thаt will replace thе lost once from ѕtrаtum соrnеum; the process takes about 1 month [11], as shown in Fig. 1.3. Further down thе stratum basale, thе cell lауеr is attached to a basement membrane that serves as demarcation or a boundary between thе epidermis and dermis. The lауеr also contains the pigment-producing cells, mеlаnосуtеѕ [12]. Melanocytes The epidermis is also responsible for giving us our skin colour due to its high pigment melanin (MLN) content. Melanocyte produces two types of MLN: pheomelanin and eumelanin. Typically, one square mm of skin contains 1000 and 2000 melanocytes and can produce two MLN types, pheomelanin and eumelanin [13].

4

1  Skin, Light, and Their Interactions

Fig. 1.3  Differentiation and migration of the basal keratinocyte, starting from SB to the SC layer

The type of MLN in the epidermis determines the skin colour; pheomelanin is prominent in light skin, while eumelanin is in dark skin. However, there is no difference in the number of melanocytes between light and dark skin. The production of MLN starts from the amino acid tyrosine via the enzyme tyrosinase [14]. Once produced, the melanocytes store MLN in small sacks called melanosomes. In light skin, melanosomes are small and contain only a few tightly packed MLN granules. In darker skin, melanosomes are larger and contain many loosely distributed MLN granules [15], as shown in Fig. 1.4. Each melanocyte establishes connections with an average of 40 keratinocytes via cellular extensions called dendrites, as shown in Fig. 1.5. MLN is then transferred to keratinocytes via a keratinocyte-initiated process. This process includes MLN exocytosis from melanocytes, followed by endocytosis of MLN by the karyocytes. Any MLN production and distribution irregularities will result in dyschromia (hyper- or hypopigmentation) [16].

Skin Anatomy

5

Fig. 1.4  Difference between dark and light skin regarding melanocytes’ MLN type and packaging

Dermis It lies between the epidermis and the subcutaneous lауеr and is about 2 mm thick. This middle lауеr of skin contains structural protein іn thе form of collagen in bulk and elastin іn minimal quantities, with a rich intertwining blood supply. The types of cells located іn thе dermis are fibroblast, mast сеllѕ, and histiocytes. The dermis’ primary cell type is the fibroblast, responsible for the dermal extracellular matrix (ECM) synthesis. The ECM includes structural proteins (such as collagen and elastin), glycosaminoglycans (such as hyaluronic acid), and adhesive proteins (such as fibronectin and laminins) [17]. The hydrophilic hyaluronic acid binds to water and increases skin hydration. The ECM component’s loss is responsible for most skin aging signs regarding sagging and laxity. The epidermis and dermis’s borders are not straight lines but wavy, forming intertwined fingers. The dermal fingers (extension) are called papilla, and the epidermal fingers (extensions) are called rete ridges [18]. Hair follicles, nerves, lymphatic vessels, and sweat glands also reside іn thе dermal lауеr of the skin and are referred to as appendageal structures or adnexa [19].

6

1  Skin, Light, and Their Interactions

Fig. 1.5  Melanocyte connection with a keratinocyte cell

Subcutaneous Layer This layer is known as the hypodermis, which іѕ the lowermost skin’s lауеr comprising mainly fat (adipose). This layer provides protection from injury, produces heat, and serves аѕ a cushion for the body [10].

Histology of Normal Skin The normal thickness of the epidermis (top layer) comprises several layers of squamous cells with the delicate basket-weave keratin (stratum corneum) on the surface. The dermis (bottom part) comprises sparse fibroblasts with abundant extracellular collagen bundles and embedded capillaries lined by a single layer of endothelial cells [20]. Figure 1.6a and b show the histology section using hematoxylin-eosin with two magnifications, 10 and 40, respectively.

Changes due to Photoaging

a

7

b

Fig. 1.6 (a) Layers of the epidermis and dermis (hematoxylin-eosin, magnification 10) [21]. (b) Layers of the epidermis and rete ridges (hematoxylin-eosin, magnification 40) [21]

Changes due to Intrinsic Aging Like all other organs, the human skin is affected by the normal aging process. The aging process is mainly induced by oxidative stress [22], resulting in a thinner dermal layer and low-quality epidermal layer [23]. This process is invertible; however, it depends on external aging factors such as photoaging.

Changes due to Photoaging Epidermis (EP) The extended exposure to the sun’s UV light affects the keratinocyte maturation and migration process and the skin’s ability to shed the old corneocytes. Therefore, the stratum corneum gets thicker, and the texture gets rougher, which results in poor light reflection (dullness) [21]. Moreover, the epidermis loses some of its functionality as a barrier allowing a higher evaporating rate (dryness) and higher irritant and pathogen penetration. Furthermore, the UV light might disrupt MLN’s production, storing, and transferring, resulting in several hyperpigmentation manifestations (melasma, lentigines, freckles) and hypopigmentation (vertigo) [24].

Dermis Overall, the human skin loses 1% of its ECM components per year. However, the UV light accelerates this rate. Since the epidermis would not block the UV light efficiently, the damaging effect might extend to ECM.  The UV light induces some enzymes responsible for elastin and collagen degradation. Therefore, photoaging accelerates ECM structural protein loss and denaturation of hyaluronic acid (dermal atrophy). Moreover, UV light might affect blood vessels in the dermis layer, resulting in visible telangiectasias and erythema. Melanocyte hyperactivation might result in high MLN concentration at the dermal level, such as in melasma [25].

8

1  Skin, Light, and Their Interactions

Fig. 1.7  Main differences between the young skin and photoaged skin Table 1.1  Average thickness of different layers of the skin on different parts of the female face [26] Skin thickness chart Anatomical region Mental Forhead Upper lip Lower lip Tip of nose Neck Cheek Glabella Eyelids

Epidermis μm 149 202 156 113 111 115 141 144 130

Dermis μm 1375 969 1061 973 918 138 909 324 215

E+D μm 1524 1171 1217 1086 1029 253 1050 468 345

Hypodermis μm 1020 1210 931 829 735 544 459 223 248

Total μm 2544 2381 2148 1915 1764 797 1509 691 593

Figure 1.7 points out the main changes induced by photoaging, such as reduced elastin and collagen, dermal and hypodermal atrophy, thinner EP, and thicker SC layer (Table 1.1). Figure 1.8 shows histology differences between photo-protected and photo-­ exposed skin [21].

Changes due to Photoaging

9

Fig. 1.8  The difference in elastic fiber destruction in photo-exposed hypertrophic skin. The photo-­ protected skin shows normal architecture, unlike photo-exposed, which shows excess mature elastic fiber deposition, which is truncated and dystrophic. Reproduced from ref. [21] with permission from the Royal Society of Chemistry

Fig. 1.9  Different stages of photoaging and its corresponding Glogau classification

Classification of Photoaging Practitioners should have the tool to objectively assess their clients and photoaging state to provide evidence-based treatments. The Glogau photoaging classification is a valuable tool if the practice does not make a skin analyzer available. Figure 1.9 shows different stages of photoaging with detailed characteristics of each stage.

10

1  Skin, Light, and Their Interactions

Fig. 1.10  Photo-numeric scale for photoaging [21]

Another system to objectively assess photoaging is the photonumeric scales developed by Ellis et  al., as shown in Fig.  1.10 [27]. The photo-numeric scale assesses assign hypertrophic facial photoaging between 0 and 8, where 0 = no photoaging, 2 = mild, 4 = moderate, 6 = severe, and 8 = very severe. Interdigitate values, i.e., 1, 3, 5, and 7, could also be assigned if appropriate [27].

Light-Based Treatment This term is widely used to describe all light-based (lasers and intense pulsed light) procedures for correct cosmetic and medical procedures. Practitioners in the aesthetic field use “photorejuvenation” to describe methods to improve skin conditions or correct a particular skin concern [28]. Therefore, choosing the correct technology requires a comprehensive understanding of the skin anatomy, the treated cosmetic issue, and the principle of laser and IPL. All photo-based treatments have one of three mechanisms of action: selective photothermolysis [29], chemical photosensitization [30], or photoacoustic effect [31].

Light-Tissue Interaction Theoretically, a laser beam can travel in a vacuum till infinity if there is no interaction. However, once a laser beam collides with an object (skin tissue), it combines four physical processes: absorption, reflection, transmission, and scattering. The object’s physical characteristics and the laser beam parameters define the most prominent type of interaction. Figure 1.11 illustrates the four different possible outcomes of the light-skin interaction.

Light-Tissue Interaction

11

Fig. 1.11  Four different possible outcomes of the light-skin interaction

Our goal is to maximize the light absorption by a specific skin component at a particular depth in light-based therapy in the aesthetic field. We use “chromophore” to refer to the skin component with the highest laser absorption properties [32].

Skin’s Chromophores All photo rejuvenation processes target the chromophores of specific skin components in the dermis and epidermis layers. These chromophores selectively absorb photons’ energy and turn it into thermal energy (heat) [33]. The main three chromophores in the human skin are: • MLN for pigmented lesion and laser hair removal (absorbs light of wavelengths between 400 and 1100 nm, with no peaks). • Water for wrinkle and dermal ECM induction (show a significant absorption peak at 3000 nm). • Hemoglobin (Hgb) and its derivatives (oxy-Hgb and deoxy-Hgb) for vascular lesion (shows strong absorption at 400–600 nm with peaks at 418, 542, and 577).

12

1  Skin, Light, and Their Interactions

MLN and Oxy-Hgp share a vast portion of the absorption spectrum. Therefore, lasers designed to target MLN (755 nm Alexandrite) have wavelengths with good MLN selectivity and low Oxy-Hgb affinity [34]. Photorejuvenation targets a specific chromophore to enhance (or prohibit) a specific process [35] or remove unwanted lesions [36]. In case of removing unwanted lesions, the thermal energy that builds up in the skin lesion that contains the chromophore ends up burning the chromophore without damaging any other skin cell, theoretically. This concept is “selective photothermolysis.” Selective Photothermolysis Photo energy (light) needs a medium to turn itself into thermal energy (heat); this medium is called a chromophore (we will discuss the three skin chromophores in detail). A chromophore is a molecule (or part of a molecule) that absorbs light in a certain spectrum range. The colour of a chromophore is the light minus that specific absorbed spectrum. To absorb photon energy, a chromophore should be able to turn it into a different form, such as thermal energy (heat). Therefore, a chromophore temperature would increase due to heat buildup, and depending on the heating rate, there are three possible scenarios: 1. The light energy has a low intensity, and the chromophore temperature heat does not rise significantly. Thus, the chromophore confines the heat, then dissipates the extra heat to the surroundings, and eventually cools down to normal temperature without disrupting the surroundings. 2. The light energy has a medium intensity, and the chromophore temperature heat rises significantly. However, the chromophore will try to cool down and return to a normal temperature as fast as possible. Thus, the chromophore will dissipate the extra heat to the surroundings at a higher rate, raising their temperature. The chromophore and its surrounding will eventually cool down with or without physiochemical changes. This phenomenon is referred to as a bystander effect, as shown in Fig. 1.12. The effect is one of the main theories that explain the laser hair removal mechanism of action. 3. The light energy is highly intense, and the chromophore temperature heat rises dramatically. The chromophore will try to cool down and return to a normal temperature as fast as possible. However, this cooling rate would not be sufficient, and the temperature will reach a point that induces physicochemical changes. The chromophore will cease to exist in the same physiochemical properties, and the surroundings might (might not) experience thermal-induced changes. This is referred to as the selective photothermolysis principle. Most of the aesthetic field’s photo-based treatments use the selective photothermolysis principle and its bystander effect to induce skin tissue changes. For this to happen, there are three key conditions: 1. The targeted tissue should have a higher concentration of a specific chromophore than its surroundings.

Light-Tissue Interaction

13

Fig. 1.12  Heat diffusion after laser exposure commonly called the bystander effect of the laser

2. We should use a specific wavelength to target that chromophore selectively. 3. We could control the temperature rise rate to induce the required photothermolysis and bystander effect, not more or less. Chemical Photosensitization Acne vulgaris light-based treatments rely, in part, on the photosensitization of porphyrins into oxygen-free radicals with antibacterial properties [37]. Photoacoustic Effect This is one physical property that is specific to the laser in short and ultrashort pulse width. In a brief explanation, a laser could induce intense vibration on a microscopic level that is mainly used for pigmentation and tattoo removal [38].

Light Parameters Wаvеlеngthѕ (nm) Thе wаvеlеngth is related to the light colour. Laser light is еxtrеmеlу mоnосhrоmаtіс (one colour) when compared to other sources of light. All of the photons that make up the laser beam have a fixed phase relationship (coherence) with respect to one another [39]. The selection of the wavelength emerges from the selective photothermolysis principle. Therefore, the wavelength should present the highest affinity between the laser and the lesion, hence the highest absorption. However, we should consider the effect of wavelength on skin-laser physical interactions [40]. Lower wavelength is associated with lower penetration due to high scattering. This makes lower wavelength laser not suitable for dermal level lesions. Moreover, it is associated with a higher risk of epidermal damage. We will discuss different

14

1  Skin, Light, and Their Interactions

available wavelengths and their indication in a later section. Figure 1.13 shows the relative penetration of the most commonly used wavelength [41]. Scientifically, we express a chromophore’s ability to absorb light in a specific wavelength by the absorption coefficient (cm−1). A higher absorption coefficient means a higher affinity between the wavelength and the chromophore [42]. Figure 1.14a and b show the three targeted chromophores in the skin and the absorption and coefficient of each wavelength [43]. We will discuss the meaning of chromophores and their relevance in aesthetic treatment in detail. As shown in Fig. 1.14b, MLN and Hgb do not show photo absorption after 1064 nm, as water becomes the main targeted chromophore. Table 1.2 shows the absorption coefficient and ratio of the three wavelengths commonly used in a picosecond range. A higher ratio indicates more specificity toward one chromophore [44]. On the contrary, intense pulsed light (IPL) is not a laser, as it is polychromatic (spectrum of wavelengths) and non-coherent. However, a practitioner can use a specific bandwidth by applying a specific filter with an upper or lower cutoff wavelength or replacing the handpiece [45]. As discussed in lasers, each wavelength band has a different penetration depth, tissue interaction, and selective chromophores [46]. Figure 1.15 shows the penetration depth of different IPL spectrums produced by different filters. Blue light is the unfiltered IPL, which includes the full spectrum between 420 and 1200 nm. As shown in Fig. 1.15, the full spectrum has the least penetration; a higher filter number correlates with a high cutoff wavelength and deeper Absorption Length 532

585

755

810

1064

1550

1927

2.94

Fig. 1.13  Relative penetration of the most commonly used wavelength

10.6

15

Light-Tissue Interaction

a

b

Fig. 1.14 (a) Absorption peak of Hgb, MLN, and water for lasers between 532 and 1064 nm. (b) Absorption peak of water for lasers between 1064 and 10,600 nm

Table 1.2  Absorption coefficient and ratio of 532 nm, 1064 nm and 755 nm Wavelength, nm Melanin abs, cm−1 Blood abs, cm−1 Absorption ratio

532 555 235 2.4:1

1,064 50 3.2 16:1

755 163 3.0 54:1

16

1  Skin, Light, and Their Interactions

Fig. 1.15  Penetration depth for different IPL spectrums produced by different filters

penetration. For example, the 690 red filter cut all light with a wavelength less than 690 nm, thus producing light between 690 nm and 1200 nm for deeper penetration. Fluence (J/cm2) If the laser beam is a string, the fluence would be the string’s density/thickness. As inferred by the unit (J/cm2), it is a measure of energy (in joules) delivered to the treated area of one cm2. Low fluence may result in less than satisfactory results, while high fluence may result in burns and adverse events [47]. Therefore, practitioners should be conservative when choosing the fluence to ensure efficacy while preserving safety. A higher affinity between the laser and skin lesion allows the practitioner to increase the fluence without risking the cells and tissues around the targeted lesion. Notice that the fluency unit does not have the “time” factor in it. Pulse Widths (Fraction of a Second) The concept of pulse width adds the “time” dimension missing from the fluence. It is essential to understand that a laser beam does not deliver energy continuously. However, it provides the energy in waves (pulses of photo-energy) with an interval between each pulse (inter-pulse delay times) [48]. To simplify this concept, let us say that we have two different laser beams, A and B (Fig. 1.16), with the following parameters • A: energy flow of 200 J/s and pulse width of 30 ms (top) • B: energy flow 200 J/s and pulse width of 10 ms (bottom)

Light-Tissue Interaction

17

Fig. 1.16  A simple illustration of two different lasers (a and b) with the same fluence and different pulse widths. The blue color is the laser pulse, and the red is the inter-pulse delay

Figure A tissue was exposed to both lasers for 100 ms; the skin would receive the same 20 J of photo energy in two pulses from both lasers; each is 10 J. However, laser B will provide energy to the skin lesions in a more intense (higher peak) but shorter pulse width than A. In another word, the continuous delivery time of the energy is different. Laser A delivers the energy in 60 ms out of 100 ms, but laser B takes only 20 ms out of the total exposure time to deliver the energy (100 ms). A laser’s short pulse duration produces a more efficient photothermolysis process to reach the clinically required temperature faster without thermal diffusion to unwanted tissues [49]. Practitioners should choose pulse width according to the target’s thermal relaxation, which is the time (in a fraction of a second) required by an object to dissipate 63% of the excess thermal energy (heat) [50]. We will discuss this concept in detail later on, but an object with a longer thermal relaxation time can confine the heat for longer times and spare unwanted heat diffusion. Therefore, targeting a lesion with a shorter relaxation time, such as melanosomes, is more challenging. Such targets dissipate (relax) heat to the surrounding tissue, making it hard to reach the required temperature inside the lesion itself. Moreover, unwanted heat diffusion might result in side effects in healthy tissues, such as burns and post-inflammatory hyperpigmentation (PIH). Therefore, practitioners should use a shorter pulse when targeting certain types of pigmentation to induce photothermolysis without giving the lesion time to cool down (by dissipating the heat to unwanted tissues) [38]. The fast heat buildup raises the lesion temperature to the required level to induce photothermolysis, minimizing heat dissipation and unwanted side effects [51]. The following figure shows a simple schematic illustration for laser A (top) and laser B (bottom). The areas colored in red refer to intra-pulse delay, which is the time between two consequent pulses. We wish to emphasize that this example is oversimplified, and relaxation time differs from the intra-pulse delay time but is an intrinsic characteristic of the target. Figure 1.17 shows one laser pulse with the same fluence but different pulse widths, long and short, A and B, respectively. As shown in Fig. 1.16a, the long pulse works well for larger targets and long relaxation times but is less effective in smaller targets. It would not be practical to induce clinical temperature in small targets using a long pulse laser. On the contrary, the short pulse is more effective in irradiating smaller targets with a short relaxation time. The heat accumulation induced by the short-pulsed

18

a

1  Skin, Light, and Their Interactions

b

Fig. 1.17  One pulse of two different lasers (a and b) with the same fluence and pulse width and how they affect large and small targets differently. The top (a) is a long pulse, and the bottom (b) is a long pulse

Fig. 1.18  Effect of the pulse width on heat diffusion after irradiation with Er:Yag laser

laser effectively exceeds the heat diffusion rate to reach clinical temperature in the targeted lesion [52]. We could use the Er:Yag laser’s pulse width to illustrate the relation between the pulse width and dynamic heat change (thermal diffusion). This laser is ablative and drills a hole in the exposed tissues. The following figure shows that the hole’s depth is almost the same regardless of the pulse width. However, long pulse width generates more heat in the surrounding tissue, as shown in Fig. 1.18. The difference is more profound if we compare a long and short pulse width laser. The following graph shows the difference in energy intensity (peak) of flashlamp-­pumped pulsed dye laser and Q-switched Nd:YAG laser.

Light-Tissue Interaction

19

Fig. 1.19  Difference between pulse width and shape between flashlamp dye laser (in green) and nanosecond laser (red), recreated from [53]

The short-pulsed laser provides a concentrated, high-intensity laser pulse usually illustrated as a needle shape, as shown in Fig. 1.19 [53]. It is essential to realize that all pulse widths (from ultrashort to ultralong) are equally important but have different applications in aesthetic fields. Moreover, the same laser wavelength has different applications and indications according to the pulse width. Other synonyms of pulse width are pulse duration and dwell time. For example, Nd:Yag laser comes in ultralong pulsed (second) for lipolysis [54], long-pulsed (ms) for laser hair removal [54], quasi-long microsecond (μs) for pigmentation [55], short nanosecond (ns) for tattoo removal [56], and ultrashort picosecond (ps) pulse width for skin rejuvenation [57]. Train of Sequential Sub-pulses Some systems can deliver the required total pulse energy in a train of consequent shots (sub-pulses) with a short intra-pulse delay [58]. The total pulse width equals the sum of the sub-pulse’s duration and the intra-pulse duration. Figure 1.20 is an illustration of the M22 IPL interface [59]. The interface shows a total pulse width of 15 ms divided into three sub-pulses with 3.8, 3.2, and 3 sub-­ pulse widths; we refer to the sum as active light emission time. The intra-pulse delay is 2.6 (between the first and second sub-pulse) and 2.4 ms (between the second and third sub-pulse). The total pulse width here is the sum of all sub-pulse widths and intra-pulse delay (3.8 + 2.6 + 3.2 + 2.4 + 3.0 = 15 ms). Photo energy may be delivered in two different patterns: A shows the traditional pattern of light-based therapy, in which the photo energy is delivered in a continuous-solid pulse, and B shows the same every delivered in three equal sequential sub-pulses. It is important to emphasize that Fig. 1.21b shows only two pulses, with three sub-pulses each, not six.

20

1  Skin, Light, and Their Interactions Pulse (ms) Number of pulses per trigger Duration of pulses in ms

3.8

Duration of pulse delay in ms Increase/Decrease Buttons ‘Same’ Button

3.2

2.6

3.0

2.4

Pulse Characteristics

Fig. 1.20  M22 IPL interface from Lumenis Fig. 1.21 (a) (Top) Two solid pulses and (b) (bottom) two pulses delivered in three equal sub-pulses

a

b

This technology is mainly utilized in IPL platforms to provide a higher safety profile, especially in patients with darker skin. An older example of this technology is the Surepulse configuration in the new Icon IPL from Cynosure for hair removal. It provides the energy in two micro-­ pulses: the first is 20 ms, then 100 ms intra-pulse delay, and finally, a 10-ms pulse (total of 130 ms). The advantage is to provide a higher peak power with the same total energy of a longer pulse, as shown in Table 1.3 [60]. More advanced IPL platforms, such as Luminus M22 with Multiple Sequential Pulsing Technology (MSP™), allow up to four sequential pulses to enhance safety and tolerability. Pulse Shape Modifying pulse width is a new advancement in laser and IPL that new practitioners usually overlook. A normal pulse’s energy distribution is bell-shaped, with a summit and two tails; a pulse with wide tails indicates energy waste [58]. The new

21

Light-Tissue Interaction Table 1.3  Advantages of using the Surepulse in Cynosure Icon IPL MaxR handpiece Pulse 1

Pulse 2

Off

Pulse 3

Benefit of greater total energy

Off MaxRs Fluence and Power Comparison

Temperature

Injury threshold

Epidermis

Pulse

Pulse width msec

Fluence j/cm2

Peak Intensity watts/cm2

Sure Pulse

130ms

62

2,500

Short Pulse

20ms

40

2,000

Long Pulse

80ms

62

775

Benefit of high peak power

Lesion

technology converts the pulse from a bell shape to a square; some examples are Advanced Fluorescence Technology (AFT) in Alma IPL systems and the squared-­ adaptive structured pulse in Fotona laser. Modifying the pulse shape aims to improve equal energy distribution and enhance some properties, such as ablation, coagulation, or photoacoustic phenomena. As discussed with the 10,600  nm CO2 laser, the ablation/coagulation ratio differs according to the pulse shape (CW, Ultrapulse, Superpulse) [61]. The chopped continuous delivery method provides high coagulation properties compared to the pulsed and superpulsed [62], as shown in Fig. 1.22a. The Superpulse mode has high peak power and relatively long pulse width, which balances ablation and coagulation, as shown in Fig. 1.22b. Ultrapulse delivers an ultrashort burst of energy and shifts the effect toward ablation with minimal coagulation effect, as shown in Fig. 1.22c. Spot Size (mm) Spot size correlates to the lens aperture that defines the diameter of the laser beam. All laser devices have adjustable spot sizes. Moreover, any adjustment in spot size would affect the maximum laser beam fluence. It is possible to get a much high laser fluence with a smaller spot size (2 mm) than with a bigger spot size (20 mm). More importantly. The spot size also affects the physical interaction between the laser and the skin and penetration depth. Smaller spot size is associated with high scattering and less penetration than laser spot size [63], as shown in Fig. 1.23. Therefore, a larger spot size had a higher safety profile due to less epidermal interaction. This effect is significant when moving from 1 to 20 mm in size. However, the spot size has an insignificant effect on the penetration depth after 20 mm. This concept is only correct within the mm range and does not apply to the fractional laser, as we will discuss later (Fig. 1.24).

22

1  Skin, Light, and Their Interactions

a

b

c

Fig. 1.22 (a) Pulse shape and effect of the CO2 laser delivered in the CW mode. (b) Pulse shape and effect of the CO2 laser delivered in Superpulse mode. (c) Pulse shape and effect of the CO2 laser delivered in Ultrapulse mode

Light-Tissue Interaction

23

Fig. 1.23  Schematic representation of the spot-size-dependent depth of penetration, recreated from [63] with permission

Fig. 1.24  Calculated penetration profiles for uniform 1, 5, 10, 20, and 40 mm width beam of equal incident fluence obtained by Monte Carlo simulation using typical skin parameters for wavelengths of 525–1100 nm, recreated from [63] with permission

Depth of Penetration The depth of laser penetration results from combining all laser parameters such as wavelength, fluence, pulse width, and spot size. Figure 1.25 is a summary of how these factors would affect the depth of penetration. The practitioner should consider the thickness of the skin on the treated area and the depth of the treated lesion (Table 1.4).

24

1  Skin, Light, and Their Interactions

Fig. 1.25  Effect of different laser parameters on the depth of penetration

Table 1.4  Absorption of different laser wavelengths by different layers and components of the human skin [64] Human skin optical properties used in the present study Basal Wavelength Optical Basal (nm) properties Epidermis layer (L)a layer (M)a 810 μa (cm-1) 0.2482 20.65 68.24 μs (cm-1) 148.02 148.02 148.02 g 0.91 0.91 0.91 940 μa (cm-1) 0.2446 12.66 41.62 μs (cm-1) 105.57 105.27 105.57 g 0.91 0.91 0.91 1064 μa (cm-1) 0.2441 8.45 27.59 μs (cm-1) 81.37 81.37 81.37 g 0.91 0.91 0.91 595 μa (cm-1) 0.3531 57.38 190.45 μs (cm-1) 148.69 148.69 148.69 g 0.8 0.8 0.8 585 μa (cm-1) 0.3709 60.71 201.50 μs (cm-1) 156.06 156.06 156.06 g 0.8 0.8 0.8 a

Basal layer (H)a 129.44 148.02 0.91 78.85 105.57 0.91 52.20 81.37 0.91 361.53 148.69 0.8 382.52 155.06 0.8

L: light pigmentation; M: moderate pigmentation; H: heavy pigmentation

Dermis 0.2576 148.02 0.91 0.2577 105.57 0.91 0.2501 81.37 0.91 0.4492 148.69 0.8 0.8 156.06 0.8

Blood 4.935 590.62 0.99 6.791 458.58 0.99 3.23 371.48 0.99 48.4 523.12 0.995 214.9 525.38 0.995

Light-Tissue Interaction

25

Repetition Rate (Hz) for the Device It is essential to understand that the pulse rate we discuss here is for the machine, not the laser itself. The repetition rate for the laser device is related to the laser-firing rate. All laser machines have manual and automatic settings; the manual settings mean the laser fires only when the operating practitioner pushes the button. Most practitioners start slow, so they fire the laser every 20  s. However, with experience, they increase the laser firing rate (repetition rate), which might be tiring for the thump. Once a practitioner gets comfortable with a repetition rate, they can use the auto setting to program the device to fire the laser in fixed intervals (e.g., on 1 Hz), which means the machine will fire the laser once every second. Therefore, the practitioner should have enough experience to move the handpiece swiftly before the laser fires again. Otherwise, the laser might result in adverse effects such as skin burns or fat atrophy. Remember that the repetition rate is affected by the spot size, as a larger spot size would limit the laser source’s ability to fire more frequently. For example, some platforms could profile a 3 Hz rate with a 5 mm spot size but only 1 Hz repetition in 20 mm.

Skin Histology Changes After Laser Interaction The type of skin cells predominately affected by lasers depends on the wavelength of light used. The specific changes in the epidermis and dermis after laser treatment depend on several factors, including the wavelength of light used, the fluence delivered to the tissue, and the type of epidermal cell that is predominantly affected. Laser Hair Removal There was a reduction in large terminal hairs with a proportionate increase in tiny vellus-like hairs in the laser-treated areas. After laser therapy, the average hair shaft diameter assessed from histological sections reduced, as seen in Fig. 1.26. Skin Rejuvenation with Color-Sensitive Laser Skin treated with a high fluence of Nd:YAG 1064 nm laser had ablative alterations to the epidermis, including separation of the keratinized and non-keratinized layers, enhanced vacuolization of deeper epidermal cells, and rupture of the epidermal-­ dermal junction. There is also an increase in epidermal thickness, which remained visible 8 weeks after laser treatment, as seen in Fig. 1.27.

26

1  Skin, Light, and Their Interactions

Fig. 1.26 Routine hematoxylin-eosin–stained section (magnification ×40) of untreated (top) and normal-mode Nd:YAG laser-treated (bottom) areas [65]

Fig. 1.27  Photomicrograph of biopsies acquired immediately after a 50 J/ cm2 treatment (right: B1, 50 J treatment, H&E stain, 20X.jpg). (Hematoxylin-­ eosin-­phloxine stain, 20× magnification originally) Following treatment, the epidermis is thicker, and its deeper layer cells are vacuolized [65]

Non-ablative Color-Blind Laser A column-like denaturation of the epidermis and dermis, a distortion of the dermo-­ epidermal junction, subepidermal coagulation within the MTZ, and an intact stratum corneum can be seen in the non-ablative version, as shown in Fig. 1.28. The

Light-Tissue Interaction

a

27

b

Fig. 1.28  Fractional non-ablative laser. (a) Focal coagulation of the epidermis and dermis with preservation of the stratum corneum after fractional 1540 nm laser (H&E ×100). (b) Focal coagulation of the epidermis and papillary dermis with preservation of the stratum corneum after fractional 1927 nm laser (H&E ×100) [67]

surrounding tissue is not damaged. Within 24  h, keratinocytes migrate from the surrounding healthy tissue to replace the thermally injured tissue [66]. Picosecond Picosecond lasers were first utilized to treat tattoos and pigmentary problems. When a microlens or diffractive lens array is attached to a picosecond laser, it produces a fractional array of focused, high-fluence micro spots surrounded by low fluence background. This energy distribution focuses on extremely high peak fluences over a limited surface area, resulting in distinct nonthermal, photomechanical histologic alterations in the epidermis and dermis in the form of cavitation, as shown in Fig. 1.29. The sizes of each of these micro spots vary depending on the device but are in the μm range [68]. Pico lasers can cause intraepidermal and dermal vacuoles at high fluences via a process known as a laser-induced optical breakdown. Laser-induced optical breakdown occurs when a chromophore, most often melanin, absorbs enough energy to exceed its irradiance threshold. When the irradiance threshold is exceeded, the chromophore releases a free electron, which starts the creation of more free electrons and the development of localized ionized plasma. The extremely intense ionized plasma can induce a fast rise in the water temperature within the tissue, resulting in the formation of steam bubbles. Cavitation occurs when tissue expands and contracts, causing pressure fluctuations in the epidermis and dermis [44]. CO2 Fractional CO2 laser creates microarrays of ablative and thermal damage; the ablation depth is related to the laser energy. Tissue ablation zones were bordered by tissue coagulation zones that spanned the epidermis and a portion of the dermis. A thin condensed lining was found on the inside wall of the lesion cavity, as seen in Fig. 1.30.

28

1  Skin, Light, and Their Interactions

a

b

c

d

Fig. 1.29  Tissue reactions after 1064  nm fractional picosecond laser treatment. Single-pulse, 1064 nm picosecond laser treatment at a 7 mm spot size and a fluence of 1.9 J/cm2 generated the fractionated appearance of cystic cavitation lesions (asterisks) throughout the lower epidermis and upper papillary dermis at regular intervals. Microscopic perinuclear vacuolar changes (arrows) were found around the areas of cystic cavitation. (a, b) Single-pulse mode and (c, d) dual-pulse mode treatment. H&E stain at original magnification (a, c) ×100 and (b, d) ×400 [69]

Er:YAG Fully Ablative Fully ablative lasers result in a full-thickness epidermal injury with partial denudation of the epidermis. The depth of the epidermal injury depends on the laser energy. At high laser fluence, full vaporization of the epidermis and superficial dermis could be achieved, as seen in Fig. 1.31 [71].

Skin Lesion Characteristics As we mentioned, laser-skin interaction depends on the laser parameters and objection characteristics.

Light-Tissue Interaction

29

a

c

b

d

Fig. 1.30  Depth of ablation of hematoxylin-eosin–stained sections of ex vivo human abdominal tissue treated with the 30 W, 10.6 mm, CO2 laser at 9.2 mJ (a), 13.8 mJ (b), 18.0 mJ (c), and 23.3 mJ (d). The arrows outline the extent of coagulation collagen zones [70]

30

a

1  Skin, Light, and Their Interactions

b

Fig. 1.31  Fully ablative Er:YAG laser. (a) Full vaporization of the epidermis and superficial dermis (H&E 3100). (b) Magnified (H&E 3200) [67]

Absorption and Contrast Different skin lesions should be targeted relatively to the most abundant chromophore. The same chromophore might exist in the lesion’s cells and surrounding cells, such as MLN, in both normal hyperpigmented skin. Moreover, in telangiectasia, two competitive chromophores may co-reside in some skin lesions, such as MLN and Oxy-Hgb [33]. Therefore, we should consider each chromophore’s concentration level and absorption before choosing a laser. The term “contrast” refers to the relative concentration of the chromophores and the absorption ratio. The most practical example is the laser of choice in hair removal; the 755 nm Alexandrite laser is more effective in laser hair removal (LHR) due to the MLN’s high absorption in the hair follicle. Therefore, the 755  nm Alexandrite laser is considered the LHR laser in skin types I–II and III as the keratinocytes do not have a high MLN concentration, thus, high contrast between the lesion and the surrounding skin. MLN does exist in darker skin types in the hair follicle and epidermis cells in relatively similar quantities. However, there is low contrast between the lesion and the surrounding skin. MLN’s high absorption of the Alexandrite makes it a less favorable choice in darker skin types III–VI and out of the choice list in skin type V due to the lack of contrast. It is worth mentioning that while it is not recommended, the 755 nm Alexandrite laser can be used in darker skin types but requires fine-tuning of the laser parameters [72]. Therefore, in such cases, we prefer to use a laser wavelength with less absorption by the chromophore, such as the 1064 nm ND:Yag. If the lesion is to pronounce (intense ecthyma in rosacea), practitioners should adjust the parameters to decrease the treatment intensity by applying one or more of the following: decreasing the fluence, increasing the pulse width, using a longer wavelength, decreasing the overlap, or using a train of sub-pulses.

Light-Tissue Interaction

31

Skin Phototypes The skin phototype assessment is one of the most critical steps a practitioner should perform before a laser or light-based treatment. Fitzpatrick Assessment The Fitzpatrick assessment is the most used method to determine the skin phototype due to the ease of implementation. The original assessment was developed in 1972 to assess skin sensitivity to sun exposure via skin color and the tendency to burn due to sunlight. Lower Fitzpatrick skin numbers indicate that skin is more prone to burn than to tan. However, practitioners have improved the original assessment in the dermatology field to include several items such as ethnicity and eye color. The improved Fitzpatrick assessment is still the most used tool to determine skin phototype. Most newly adapted skin type assessment forms have four fields: genetic background and deposition, genetic deposition, reaction to sun exposure, and tanning habits with 10–12 multiple-choice questions, as shown in Tables 1.5 and 1.6. The practitioner should help the client choose one of the four suggested answers and grade each question accordingly. The client’s skin phototype is directly related to the total score of the questionnaire. A higher score is related to higher skin type and risks with photo treatments such as epidermis burns and post-inflammatory pigmentation. Table 1.6 is a modern skin type assessment that includes three factors: genetic disposal, tanning habits, sun exposure, and heritage score. Several other assessments have been published, such as Lancer, Goldman, FANOUS, and Tayler scales [73]. Some studies argued that all these assessments are subjective and do not provide a reliable measure of laser-skin interaction [74]. Despite the improvements, several studies have criticized the objectivity and validation of the self-reported assessment. Therefore, other methods, such as Wood’s lamp and skin colorimeter, have been developed to evaluate skin phototypes better. Skin Reflectance Colorimeter The new handheld colorimeters emit light of a specific spectrum and measure the light’s wavelength and intensity reflected by the skin [75]. This data is converted into a colorimetric value and suggests skin color. One deficiency of these devices is that they measure only a small skin area. Therefore, the practitioner should perform multiple tests and ensure to include the darker spots if they exist.

32

1  Skin, Light, and Their Interactions

Table 1.5  Skin type assessment with 12 multiple-choice questions that take genetic and heritage disposition into account Genetic Disposition Score

0

1

Your eye color?

Light blue, Gray, Green

Blue, Gray, or Green

Natural color of your hair?

Sandy Red

Blond

Color of your nonexposed skin?

Reddish

Do you have freckles on unexposed areas?

Many

2

3

Blue

4

Dark Brown

Brownish Black

Chestnut/ Dark Blond

Dark Brown

Black

Very Pale

Pale with beige tint

Light Brown

Dark Brown

Several

Few

Incidental

None

12

Total score for genetic disposition:

Reaction to Sun Exposure Score

0

1

What happens when you stay too long in the sun?

Painful redness, blistering, peeling

Blistering followed by peeling

Burn sometimes followed by peeling

2

Rarely burn

3

Never burn

4

To what degree do you turn brown?

Hardly or not at all

Light color tan

Reasonable tan

Tan very easily

Turn dark brown quickly

Do you turn brown within several hours of sun exposure?

Never

Seldom

Sometimes

Often

Always

How does your face react to the sun?

Very sensitive

Sensitive

Normal

Very resistant

Never had a problem

10

Total Score for reaction to sun exposure:

Tanning Habits 3

4

Last exposure to the sun or tanning booth / cream?

Score

More than 3 months ago

0

2-3 months ago

1

1-2 months ago

2

Less than 1 month ago

Less than 2 weeks ago

Did you expose the area to be treated to the sun?

Never

Hardly ever

Sometimes

Often

Always

0

Total Score for tanning habits:

Heritage Score For each parent of african american or east indian descent add 10 points My Skin Type Score: 32 My Skin Type: V Skin Type Score

Fitzpatrick Skin Type

0-7 8-16 17-25 25-30 31-34 Over 35

I II III IV V VI

0

10

20

33

Light-Tissue Interaction Table 1.6  Simple skin-type assessment with ten multiple-choice questions SAMPLE SKIN TYPING

Client Name:

Date:

Score:

0 What is your eye color?

Light blue or gray

Blue or green

What is the natural color of your hair?

Red, Sandy red

Blonde

What is the color of your skin (unexposed areas)?

Reddish

Very pale

Do you have freckles on sun-exposed areas?

Many

Several

What happens when you stay in the sun too long?

Add above for Total score:

1

Hardly any or not at all

Do you turn brown several hours after sun exposure?

Never

How does your face respond to the sun?

Very sensitive

When did you last expose yourself to the sun, tanning bed or self-tanning creams? How often is the area you want to have treated exposed to the sun?

0-7 8-16

Light tan

Seldom

3

4

Dark brown

Brownish black

Dark brown

Black

Pale with beige tint

Light brown

Dark brown

Few

Incidental

None

Rarely burns

Never had burns

Painful Burns, Blistering redness, sometimes followed blistering followed by by peeling peeling peeling

To what degree do you turn brown?

Match your total score with the corresponding Skin Type.

2 Hazel Light brown Dark blonde chestnut Brown

Reasonable Tan very tan easily

Turn dark brown quickly

Sometimes

Often

Always

Sensitive

Normal

Very resistant

Never had a problem

More than 3 months ago

2-3 months ago

1-2 months ago

Less than 1 month ago

Less than 2 weeks ago

Never

Hardly ever

Sometimes

Often

Always

Fitzpatrick Skin Type:

I II

17-25

III

26-30

IV

Over 30

V-VI

34

1  Skin, Light, and Their Interactions

Older devices, such as Mexameter MX 18 (Courage+Khazakauses, Germany), use only a narrow-band reflectance spectrophotometer. Other devices, such as Antera 3D (Miravex Limited, Ireland), use seven different wavelengths. However, these devices’ data is not absolute and may change according to external variables such as previous tanning and room temperature. Other than the Mexameter and Antera 3D, we are aware of three handheld devices to assess skin color: Chroma Meter (Minolta, Japan), DSM III (Cortex technology, Denmark), and Skintel (Cynosure). Some new LHR platforms’ handpiece is integrated with an internal skin colorimeter to help practitioners choose the best treatment settings. For example, the Skintel melanin reader is integrated with the Cynosure Icon IPL and Vectus diode laser. After taking three readings for the treatment area, the software converts the reading into melanin index (MI) and communicates with the treatment platform to suggest a test spot parameter [76], as shown in Figs. 1.26 and 1.32. It is important to understand that these skin types do not correlate with an absolute MI value but with a range [28], as shown in Fig. 1.28; for example, the melanin index of 20 is shared between skin types III and IV. Therefore, practitioners should always seek and observe clinical endpoints (Fig. 1.33).

Fig. 1.32  Skintel device, a handheld melanin reader by Cynosure [76]

Fitzpatrick Skin Type

VI V IV III I-II

0

10

20

30

40 50 60 Melanin Index

Fig. 1.33  MI range for each skin type [76]

70

80

90

100

Light-Tissue Interaction

35

Thermal Relaxation Time (TRT) and Size As explained before, as the lesion’s chromophores receive laser pulses, the heat builds up. However, the lesion’s cells that contain the chromophore are not thermally isolated from surrounding cells. Therefore, it starts dissipating the thermal heat to adjacent cells. Thermal relaxation is an object’s ability to cool down by dissipating thermal energy to the surroundings [50]. The TRT is a measure of the time (in a fraction of a second) required by an object to dissipate 63% of the excess thermal energy (heat). TRT is directly related to the density and size of the chromophore in the lesion. A lesion with high laser absorption and short relaxation time would damage the surrounding cells. Therefore, a short-pulsed laser with high energy is the laser of choice as it removes the lesion before it can dissipate the heat and damage surrounding cells. Q-switch ns and the newer picosecond lasers are examples of high-energy short-pulsed lasers. The thermal relaxation’s secondary (by standard) effect should be controlled to exert the desired clinical outcomes without side effects. For example, laser hair removal relies on the hair strand’s ability to relax the heat by dissipating it to the follicle’s germinative cells. However, if the heat exceeded the clinical limit, it would result in burns and other side effects. Small targets like melanosomes cool down extremely fast, and they do not retain the photo-thermal energy (heat) to a specific clinical level. Therefore, such targets should be exposed to a high-energy short-pulsed laser. The TRT and the pulse width are strongly tied together but from different perspectives, as discussed later. Depth of the Lesion All laser targets for photo rejuvenation purposes exist in the epidermal and dermal levels, a total of 2.1 mm. Therefore, we can adjust the laser settings to provide the required penetration to reach the lesion and protect the other tissues—less than optimal laser penetration (too shallow or too deep) results in unwanted adverse reactions [77]. Most new laser systems are equipped with a computing unit to suggest adequate parameters relevant to the lesion depth, intensity, and skin phototype [78]. Moreover, the parameter of fractional lasers such as CO2 and Er:Yag is chosen in relevance to the required depth of ablation or coagulation. If a lesion exists in variable depth (rosacea and melasma), practitioners should target the deeper section and adjust parameters to correct the superficial parts [79].

36

1  Skin, Light, and Their Interactions

References 1. Kolárová H, Ditrichová D, Wagner J. Penetration of the laser light into the skin in vitro. Lasers Surg Med. 1999;24(3):231–5. 2. Vestita M, Tedeschi P, Bonamonte D. Anatomy and physiology of the skin. In: Textbook of plastic and reconstructive surgery. Springer; 2022. p. 3–13. 3. Yousef H, Alhajj M, Sharma S. Anatomy, skin (integument), epidermis. 2017. 4. Epstein WL, Maibach HI. Cell renewal in human epidermis. Arch Dermatol. 1965;92(4):462–8. 5. Cua AB, Wilhelm KP, Maibach H. Frictional properties of human skin: relation to age, sex and anatomical region, stratum corneum hydration and transepidermal water loss. Br J Dermatol. 1990;123(4):473–9. 6. Ya-Xian Z, Suetake T, Tagami H.  Number of cell layers of the stratum corneum in normal skin–relationship to the anatomical location on the body, age, sex and physical parameters. Arch Dermatol Res. 1999;291(10):555–9. 7. Murphrey MB, Miao JH, Zito PM. Histology, stratum corneum. StatPearls; 2020. 8. Wertz P. Epidermal lamellar granules. Skin Pharmacol Physiol. 2018;31(5):262–8. 9. Marks R, Edwards C. The measurement of photodamage. Br J Dermatol. 1992;127(S41):7–13. 10. Wysocki AB.  Skin anatomy, physiology, and pathophysiology. Nurs Clin North Am. 1999;34(4):777–97. v 11. Kolarsick PA, Kolarsick MA, Goodwin C. Anatomy and physiology of the skin. J Dermatol Nurses Assoc. 2011;3(4):203–13. 12. Lin JY, Fisher DE. Melanocyte biology and skin pigmentation. Nature. 2007;445(7130):843–50. 13. Hennessy A, et al. Eumelanin and pheomelanin concentrations in human epidermis before and after UVB irradiation. Pigment Cell Res. 2005;18(3):220–3. 14. D’Mello SA, et al. Signaling pathways in melanogenesis. Int J Mol Sci. 2016;17(7):1144. 15. Lu H, et al. Melanin content and distribution in the surface corneocyte with skin phototypes. Br J Dermatol. 1996;135(2):263–7. 16. Villegas AGD, Hernández CG, Mendoza IA. News in the treatment of melasma. Dermatología Cosmética, Médica y Quirúrgica. 2021;18(4):307–17. 17. Rippa AL, Kalabusheva EP, Vorotelyak EA.  Regeneration of dermis: scarring and cells involved. Cell. 2019;8(6):607. 18. Topczewska JM, et  al. Mechanical stretching stimulates growth of the basal layer and rete ridges in the epidermis. J Tissue Eng Regen Med. 2019;13(11):2121–5. 19. Lavker RM, Sun T-T. Epidermal stem cells. J Investig Dermatol. 1983;81(1):S121–7. 20. Han A, Chien AL, Kang S. Photoaging. Dermatol Clin. 2014;32(3):291–9. 21. Watson RE, Griffiths CE. Cutaneous photoaging. Royal Society of Chemistry; 2019. 22. Poljšak B, Dahmane RG, Godić A.  Intrinsic skin aging: the role of oxidative stress. Acta Dermatovenerol Alp Pannonica Adriat. 2012;21(2):33–6. 23. Guinot C, et al. Relative contribution of intrinsic vs extrinsic factors to skin aging as determined by a validated skin age score. Arch Dermatol. 2002;138(11):1454–60. 24. Bhawan J, et al. Photoaging versus intrinsic aging: a morphologic assessment of facial skin. J Cutan Pathol. 1995;22(2):154–9. 25. Poon F, Kang S, Chien AL.  Mechanisms and treatments of photoaging. Photodermatol Photoimmunol Photomed. 2015;31(2):65–74. 26. Chopra K, et al. A comprehensive examination of topographic thickness of skin in the human face. Aesthet Surg J. 2015;35(8):1007–13. 27. Griffiths CE, et al. A photonumeric scale for the assessment of cutaneous photodamage. Arch Dermatol. 1992;128(3):347–51. 28. Elsaie ML, Lloyd HW.  Latest laser and light-based advances for ethnic skin rejuvenation. Indian J Dermatol. 2008;53(2):49. 29. Altshuler G, et  al. Extended theory of selective photothermolysis. Lasers Surg Med. 2001;29(5):416–32.

References

37

30. Maisch T, et al. Fast and effective: intense pulse light photodynamic inactivation of bacteria. J Ind Microbiol Biotechnol. 2012;39(7):1013–21. 31. Shubnyy A, et al. Laser bleaching of tattoos: a new approach. Quantum Electron. 2021;51(1):8. 32. Waibel JS. Photorejuvenation. Dermatol Clin. 2009;27(4):445–57. 33. Young AR. Chromophores in human skin. Phys Med Biol. 1997;42(5):789. 34. Zijlstra W, Buursma A, Meeuwsen-Van der Roest W. Absorption spectra of human fetal and adult oxyhemoglobin, de-oxyhemoglobin, carboxyhemoglobin, and methemoglobin. Clin Chem. 1991;37(9):1633–8. 35. Bjerring P, et al. Facial photo rejuvenation using two different intense pulsed light (IPL) wavelength bands. Lasers Surg Med. 2004;34(2):120–6. 36. Zoccali G, et  al. Melasma treated with intense pulsed light. Aesthet Plast Surg. 2010;34(4):486–93. 37. Nouri K, Villafradez-Diaz LM. Light/laser therapy in the treatment of acne vulgaris. J Cosmet Dermatol. 2005;4(4):318–20. 38. Watanabe S. Basics of laser application to dermatology. Arch Dermatol Res. 2008;300(1):21–30. 39. Silfvast WT. Laser fundamentals. Cambridge University Press; 2004. 40. Niemz MH. Laser-tissue interactions. Springer; 2007. 41. Carroll L, Humphreys TR. LASER-tissue interactions. Clin Dermatol. 2006;24(1):2–7. 42. van Gemert MJ, Welch A. Clinical use of laser-tissue interactions. IEEE Eng Med Biol Mag. 1989;8(4):10–3. 43. Small R. A practical guide to laser procedures. Lippincott Williams & Wilkins; 2015. 44. Md ET, Jennings J. A comparative study with a 755 nm picosecond Alexandrite laser with a diffractive lens array and a 532 nm/1064 nm Nd: YAG with a holographic optic. Lasers Surg Med. 2018;50(1):37–44. 45. Babilas P, et al. Intense pulsed light (IPL): a review. Lasers Surg Med. 2010;42(2):93–104. 46. Husain Z, Alster TS. The role of lasers and intense pulsed light technology in dermatology. Clin Cosmet Investig Dermatol. 2016;9:29. 47. Trivedi M, Yang F, Cho B. A review of laser and light therapy in melasma. Int J Women’s Dermatol. 2017;3(1):11–20. 48. Anderson RR. Lasers in dermatology—a critical update. J Dermatol. 2000;27(11):700–5. 49. Fitzpatrick RE, Goldman MP, Ruiz-Esparza J. Clinical advantage of the CO2 laser superpulsed mode: treatment of verruca vulgaris, seborrheic keratoses, lentigines, and actinic cheilitis. J Dermatol Surg Oncol. 1994;20(7):449–56. 50. Choi B, Welch AJ. Analysis of thermal relaxation during laser irradiation of tissue. Lasers Surg Med. 2001;29(4):351–9. 51. Kono T, et al. A local rapid temperature rise model for analyzing the effects of irradiation on human skin in laser treatments. Int J Heat Mass Transf. 2021;171:121078. 52. Nilsen LTN, et al. Epidermal melanin absorption in human skin. In: Laser-tissue interaction and tissue optics. International Society for Optics and Photonics; 1996. 53. Goo BL. Clinical effectiveness of low-fluence 585 nm Q-switched Nd: YAG laser treatment on persistent facial erythema after adult type acne treatment: a preliminary study. 2013. 54. Lukac M, et  al. QCW pulsed Nd: YAG 1064  nm laser lipolysis. J Laser Health Acad. 2009;4(1):24–34. 55. Jung JY, et al. Prospective randomized controlled clinical and histopathological study of acne vulgaris treated with dual mode of quasi-long pulse and Q-switched 1064-nm Nd: YAG laser assisted with a topically applied carbon suspension. J Am Acad Dermatol. 2012;66(4):626–33. 56. Gorsic M, et al. Evaluation of the efficacy of tattoo-removal treatments with Q-switch laser. J Laser Health Acad. 2013;2013:21–6. 57. Wu DC, et al. A systematic review of picosecond laser in dermatology: evidence and recommendations. Lasers Surg Med. 2021;53(1):9–49. 58. Town G, et al. Measuring key parameters of intense pulsed light (IPL) devices. J Cosmet Laser Ther. 2007;9(3):148–60. 59. Stellar M22 - Lumenis. 2021. https://lumenis.com/aesthetics/products/stellar-­m22/.

38

1  Skin, Light, and Their Interactions

60. Icon Cynosure. 2021. https://www.cynosure.com/product/palomar-­icon-­aesthetic-­system/. 61. Alexiades-Armenakas MR, Dover JS, Arndt KA. The spectrum of laser skin resurfacing: nonablative, fractional, and ablative laser resurfacing. J Am Acad Dermatol. 2008;58(5):719–37. 62. Lumenis M22 operator manual. Lumenis M22 operator manual. 2021. https://www.medwrench.com/documents/view/7211/lumenis-­m22-­operator-­s-­manual. 63. Ash C, et al. Effect of wavelength and beam width on penetration in light-tissue interaction using computational methods. Lasers Med Sci. 2017;32(8):1909–18. 64. Lister T, Wright PA, Chappell PH.  Optical properties of human skin. J Biomed Opt. 2012;17(9):090901. 65. Dayan S, et al. Histological evaluations following 1,064-nm Nd: YAG laser resurfacing. Lasers Surg Med. 2003;33(2):126–31. 66. Laubach HJ, et  al. Skin responses to fractional photothermolysis. Lasers Surg Med. 2006;38(2):142–9. 67. Chen SX, et al. Review of lasers and energy-based devices for skin rejuvenation and scar treatment with histologic correlations. Dermatol Surg. 2022;48(4):441–8. 68. Tanghetti EA. The histology of skin treated with a picosecond alexandrite laser and a fractional lens array. Lasers Surg Med. 2016;48(7):646–52. 69. Chung HJ, et al. Pattern analysis of 532-and 1064-nm microlens array-type, picosecond-domain laser-induced tissue reactions in ex vivo human skin. Lasers Med Sci. 2019;34(6):1207–15. 70. Saedi N, Petelin A, Zachary C. Fractionation: a new era in laser resurfacing. Clin Plast Surg. 2011;38(3):449–61. 71. Drnovšek-Olup B, Beltram M, Pižem J. Repetitive Er: YAG laser irradiation of human skin: a histological evaluation. Lasers Surg Med. 2004;35(2):146–51. 72. Galadari I. Comparative evaluation of different hair removal lasers in skin types IV, V, and VI. Int J Dermatol. 2003;42(1):68–70. 73. Roberts WE. Skin type classification systems old and new. Dermatol Clin. 2009;27(4):529–33. 74. Fasugba O, Gardner A, Smyth W. The Fitzpatrick skin type scale: a reliability and validity study in women undergoing radiation therapy for breast cancer. J Wound Care. 2014;23(7):358–68. 75. Matias AR, et  al. Skin colour, skin redness and melanin biometric measurements: comparison study between Antera® 3D, Mexameter® and Colorimeter®. Skin Res Technol. 2015;21(3):346–62. 76. Yaroslavsky I, et al. Objective measurement device for melanin optical density: dosimetry for laser and ipls in aesthetic treatments. 2017. 77. Wang-Evers M, et al. Assessment of a 3050/3200 nm fiber laser system for ablative fractional laser treatments in dermatology. Lasers Surg Med. 2022;54(6):851–60. 78. Alhallak K, et al. Skin, light and their interactions, an in-depth review for modern light-based skin therapies. J Clin Derm Ther. 2021;7(2):81. 79. Fischer DL, et al. Intense pulsed light for the treatment of pigmented and vascular disorders and lesions: a review. Dermatol Rev. 2021;2(2):69–81.

Chapter 2

Laser and Intense Pulsed Light

The acronym LASER, which is frequently used as a stand-alone word, stands for the more technical scientific term “light amplification by stimulated emission of radiation.” Some materials respond to stimulation by emitting light. This light is categorized as a laser if it possesses specific physician characteristics, such as a single wavelength (monochromatic), collimated (parallel rays), and a highly focused beam [1]. Figure 2.1 demonstrates that intense pulsed light (IPL) is not a laser because it is polychromatic (spectrum of wavelengths) and non-coherent high-energy light [2]; despite these distinctions, the majority of practitioners use the term laser to refer to laser and IPL machines. Figure 2.1b is a simple illustration that categorizes lasers according to its aesthetic indication.

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 K. Alhallak et al., The Ultimate Guide for Laser and IPL in the Aesthetic Field, https://doi.org/10.1007/978-3-031-27632-3_2

39

40

2  Laser and Intense Pulsed Light

a IPL system

Lasers

Polychromatic (a band of wavelengths)

Monochromatic (only one wavelength)

Non-coherent (waves are not in phase)

Coherent (waves are always in phase)

Defocused light

Parallel light (directional)

b Ablative lasers

Nonablative lasers

Red vascular ectasis

Moderate to severe rhytids’ dyschromia

2790 (YSGG) 2940 (Er:YAG) 10600(CO2)

585 595

532 IPL

Pigmentation

755 1064

Mild skin resurfacing

1540 1550 1565

1320 1410 1440

Hair removal

755 810 1064 IPL

Tatto removal

Q-switched 532 585 650 755 1064

Fig. 2.1 (a) Summary of differences in the emitted light between laser and IPL. (b) Common use of photo-based treatment for common aesthetic conditions

IPL Intense pulsed light (IPL) devices emit a broad band of high-energy light, typically between 400 and 1200 nm in wavelength [3]. At the end of the handpiece (applicator), which is in direct contact with the skin, there is a sapphire or quartz crystal;

IPL

41

this crystal serves two purposes: (1) contact cooling to protect the epidermis layer and (2) as a photon energy delivery medium. All IPL systems are available in a variety of crystal sizes (from small to large) to accommodate various treatments and areas. In addition to the standard 400–1200 nm range, some IPL systems, such as Cutera’s Solera Titan, emit infrared pulsed light sources between 1100 and 1800 nm [4]. Most IPL systems include a contact cooling system to make treatment more comfortable and protect the epidermis [5]. However, practitioners may require separate cooling systems, such as forced refrigerated air (chiller) or cryogen spray, to cool down sensitive lesions (such as melasma) prior to and after treatment [6, 7]. IPL systems enable practitioners to control light characteristics such as light band wavelength in nanometers (400–1200 nm), fluence in joules per square centimeter (1–30 J/cm2), and pulse width (duration) in milliseconds (0.5–100 ms). Here are some “rules of thumb” when using IPL for skin lesions other than hair removal: • For superficial lesions on lighter skin (up to skin type IV), use the 560 nm filter. • For medium-depth and superficial lesions in darker skin, use the 590 nm filter (skin type IV and light V). • When the desired effect is deeper in the dermis or the skin is dark (skin type V), use the 640 nm filter. • Reduce the fluence by 1 to 2 joules when treating the neck, hands, arms, and chest. Reduce the fluence even more when treating the chest. • Use the same fluence when treating body areas other than the neck, hands, arms, and chest. • If lesions begin to clear and show less contrast, practitioners should increase the intensity in subsequent sessions. Increase the fluence by 1 to 2 J/cm2 per session as the lesions lighten during the treatment sessions. • If available, use the 515 nm filter on stubborn lesions and skin types I and II. If the system supports such a delivery model, potential side effects may be reduced if the energy is delivered in the form of a 2–3 sequential pulse train. • Larger treatment tips deliver deeper penetration. • Avoid treating areas with tattoos or permanent ink. • Reduce fluence in areas close to the bone because of light reflection and fatty areas because of heat retention. • If a practitioner does not see a good clinical response, they can increase the intensity of the treatment by doing one of the following: increasing the fluence by 1 J/cm2, decreasing the pulse duration by 1 ms, or using a different filter (or handpiece) with a lower cutoff wavelength. • Some clinical responses or adverse effects may take up to 24 hours to manifest fully.

42

2  Laser and Intense Pulsed Light

Types of IPLS IPL with Interchangeable Filters

Sebaceous gland

mm 0

1

2 Sweat gland

3 Blood vessels

4

650mm

Hair

440mm

Fig. 2.2  Penetration depth with four different IPL filters, 440 nm, 540 nm, 580 nm, and 650 nm

540mm 580mm

These systems typically include a single handpiece and multiple replaceable filters. The filters slide and lock into a slot in the handpiece (plug and play). The inserted filter contains one or more cutoff filters to eliminate the unwanted light band. For example, the traditional 615 filter, mostly used in hair removal, eliminates light with a wavelength lower than 615 nm to target melanin. More advanced systems include filters that provide a narrower light band, such as the Lumenis M22 acne filter, which offers dual bands of 400–600 and 800–1200 nm for more effective acne treatment [8]. The depth of light penetration is multifactorial, but one of the important factors determining it is wavelength. The higher the filter in the IPL light emission range, the deeper the penetration and the less epidermis effect (higher safety). Figure 2.2 shows how each filter produces a different light spectrum and thus a different penetration depth. It shows that the higher the filter number, the narrower the light band and the deeper the penetration [9]. IPL filter technology has progressed over the last two decades to provide consistent energy distribution through the pulse without reducing the energy output [10]. Besides, the new generations of IPL systems could emit the photo energy in a train of sequential pulses (double or triple) to enhance treatment safety [11].

IPL

43

There are numerous IPL systems available with replaceable filters. Therefore, this book will not be able to cover all of them. We chose to focus on systems with which we have firsthand experiences, such as Vydence IPL-Sq and the Lumenis M22 and Sciton BBL Joule. The comparison includes the filter technology, pulse width, irradiance mode, train of pulses, and cooling system. We will also attempt to capture any features that we believe are noteworthy. Any light-based therapy can be delivered in either dynamic or static mode; both should heat the target tissues to clinical temperatures. The platform’s dynamic (in-motion) mode is commonly referred to as painless, as the heat builds up gradually in the tissues via a continuous movement of the applicator [12]. The static (stamping) mode involves zapping the lesion with a strong pulse before moving on to the next area [13]. Dynamic mode is mainly used for hair removal in IPL and diode laser machines [14]. It is important to note that we will not recommend one system or manufacturer over another; instead, we aim to provide this information to the reader to make an educated decision. Comparison Table 2.1 compares three IPL systems with interchangeable filters in terms of filter technology, pulse width, irradiance mode, pulse sequence, cooling mechanism, and other characteristics.

Table 2.1  Comparison of different IPL systems with interchangeable filters System name IPL-Sq Vydence

Filter technology Square Pulse Technologya

M22 Optimal Pulse Lumenis Technology OPT™) and Multiple Sequential Pulsing (MSP™)b

Train of Pulse width Irradiance sequential pulses (ms) mode 5–100 Static No

4–20

Static

Cooling Continuous contact cooling (not adjustable) Continuous Yes (1, 2, contact and 3 cooling (not pulses) Pulse delay adjustable) 5–150 ms

Features A second-­ generation IPL that can be added to the Ethera platform The M22 is a comprehensive workstation that could be custom built with Q-switch YAG and 1565 nm fractional laser OPT thin filters, dual brand filters for acne and vascular lesion (continued)

2  Laser and Intense Pulsed Light

44 Table 2.1 (continued) System name BBL Joule Sciton

Filter technology Smart Filter with Finesse Spot Adapters™c

Train of Pulse width Irradiance sequential pulses (ms) mode 5–200 Static and No dynamic

Cooling Continuous contact cooling adjustable, 0–30 °C

Features The only IPL with dynamic mode that offers a no-pain option. SkinTyte (S.T.) special filters, part of the Joule comprehensive platform

According to Vydence, the IPL-Sq® technology promotes controlled and microprocessor delivery of energy, released evenly throughout the pulse, in contrast to traditional IPL equipment in which the energy discharge is uncontrolled, and thus the energy delivered at the beginning of the pulse duration is greater than that delivered at the end. This discharge configuration (1) prevents the formation of critical risk areas that, in practice, can result in undesirable effects; (2) ensures the emission of energy with a constant and uniform spectrum along the pulse, resulting in a more effective therapeutic outcome; and (3) increases the procedure’s safety and efficacy. This technology is not exclusive to Vydence, as all second-generation IPL systems are equipped with the square pulse feature. Table 2.2 lists the technical specifications for IPL-Sq b Lumenis claims that OPT provides gentler, more comfortable, and patient-friendly procedures with lower effective fluences • High peak power, shorter pulses—ideal for IPL skin treatments using photorejuvenation and treatment of benign pigmented lesions • Advanced OPT will also allow determining the specific fluence per sub-pulse when using multiple-sequential pulsing (MSP), for fine-tuned treatment settings [15]. Lumenis launched the Stellar M22 with three SapphireCool™ lightguides to provide better continuous contact cooling for patient comfort. At the time of writing, a new version of the M22 with advanced OPT (AOPT) had just been released in China. The benefits of AOPT over OPT are not yet clear. Table 2.3 lists the M22 system specifications c According to Sciton, Smart Filter with Finesse Spot Adapters™ provides an easy and quick way to change filters and reach difficult spots [16]. Table 2.4 lists different handpieces for the Joule system and their indications. Table 2.3 lists indications of different handpieces from Joule systems a

Table 2.2 IPL-Sq® technical specifications

IPL spectrum Filters Spot size Vascutip TM Fluence Pulse width Cooling system Repetition rate

400–1200 nm 400, 540, 580, 640 and 695 nm 40 × 12 nm 8 mm and 12 × 12 mm Up to 33 J/cm2 5 to 100 ms Built-in sapphire contact cooling Up to 2 Hz

IPL

45

Table 2.3 M22® technical specifications IPL spectrum Filters

Fluence Pulse duration Pulse delay Pulse characteristic Repetition rate Spot size Cooling ResurFX™ Wavelength Pulse energy Pulse characteristic Pattern shapes Beam density Repetition rate Tip Spot size Cooling Multi-Spot™ Nd:YAG Wavelength Fluence Pulse duration Pulse delay Pulse characteristic Repetition rate Spot size Cooling Q-Switched Nd:YAG Wavelength Fluence Pulse duration Pulse characteristic Repetition rate Spot size

400–1200 nm Acne (400–600 and 800–1200); 515 nm Vascular (530–650 and 900–1200); 560 nm; 590 nm; 615 nm; 640 nm; 695 nm; 755 nm 8 × 15 mm—up to 35 J/cm2 15 × 35 mm—up to 35 J/cm2 6 mm round—up to 56 J/cm2 4–20 ms 5–150 ms Multiple Sequential Pulsing Up to 1 Hz 35 × 15 mm2; 15 × 8 mm2, 6 mm Continuous contact cooling 1565 nm 10–70 mJ per micro-beam CoolScan™ Scanner Line, square, rectangle, circle, doughnut, hexagon Up to 500 micro-beams/cm2 0.5–2 Hz Sapphire; Precision Up to 18 mm Continuous contact cooling 1064 nm 10–225 J/cm2 2–20 ms 5–100 ms Multiple Sequential Pulsing Up to 1 Hz 6 mm; 2 × 4 mm2; 9 mm Continuous contact cooling 1064 nm 0.9–14 J/cm2 6–8 ns Top-Hat 0.5–5.0 Hz 2; 2.5; 3.5; 4; 5; 6 and 8 mm

46

2  Laser and Intense Pulsed Light

Table 2.4 BBL® technical specifications

Table 1.3 BBL® TECHNICAL SPECIFICATIONS IPL spectrum Filter

20 – 1400 nm 420 nm, 515 nm, 560 nm, 590 nm, 640 nm, 695 nm, 800 nm Up to 30 J/cm2 Up to 200 msec Up to 1 pulse-per-second Continuous thermoelectric sapphire plates Adjustable from 0 - 30 ˚C 15 x 45 mm 15 x 15 mm square, 11 mm & 7 mm round

Fluence Pulse Width Repetition Rate Cooling Method Skin Cooling Spot Size Finesse Adapters

ProFractional-XC™

diVa®

ClearScan ALX™

Contour TRL™

ClearScan YAG™

ThermaScan™

ClearSense™

ProLipo PLUS ™

CelluSmooth™

Pro-V™

BBL™

SkinTyte™

Forever Bare BBL™

2940 Er:YAG

1470 Diode & 2940 Er:YAG

755 Alex.

2940 Er:YAG

1064 Nd:YAG

1319 Nd:YAG

1064 Nd:YAG

1064 / 1319 Nd:YAG

1319 Nd:YAG

1319 Nd:YAG

420 to 1400 Smart Filters

590 to 1400 Smart Filters

590 to 695 Smart Filters

Wavelength (nm) Acne

•

Acne Scars

•

Pigmented Lesions

SKIN

BBL

Halo™

JOULE Module

FIBER

1470 Diode & 2940 Er:YAG

Handpiece

•

Scar Revision

•

•

•

•

•

•

Skin Resurfacing

•

•

•

Skin Texture Improvement

•

•

•

•

•

•

• •

FY BBL Concept

BODY

VASCULAR

Wrinkles Vascular Lesions

•

•

Telangiectasia

•

•

•

Reticular/Spider Veins

•

•

Endovenous Ablation

•

Laser Lipolysis

•

HD Lipo Sculpting

•

Lumpy, Dimpled Skin

•

HAIR & SPECIALTIES

Appearance of Firmer Skin

•

Permanent Hair Reduction

•

•

Onychomycosis Warts Vaginal Therapy

• •

•

•

•

•

•

•

IPL

47

Fig. 2.3  IPL handpiece with a replaceable filter; the filter is marked as 515 nm

IPL with Interchangeable Handpieces (Applicators) Handpieces in these systems are outfitted with stationary filters. As a result, practitioners should switch handpieces to obtain a different light band wavelength. There are numerous options for this type of IPL system on the market. This book will cover three systems: Cynosure’s Icon (formerly Palomar Icon), Syneron-Nordlys Candela’s IPL (formerly Ellipse IPL), and Alma’s Harmony XL. Figure 2.3 depicts some of these IPL machines’ key characteristics and applicators. Comparison Table 2.5 compares three IPL systems with replaceable handpieces: Nordlys Ellipse from Candela, Icon Palomar from Cynosure, and Harmony from Alma in filter technology, pulse width, irradiance mode, sequence of pulses, cooling mechanism, and different features.

Each handpiece has three pulse widths to choose from. See Table XX

Train of sequential pulses Yes (1, 2, 3, and 4 pulses) duration of pulse train 0.5–700 ms

Up to 81 Surepulse for hair removal (20 ms laser on, 100 ms delay, 10 ms laser on) with a high-power peak Static NA and dynamic

Fluence (J/cm2) 2–26

Continuous contact cooling (not adjustable)

Adjustable continuous contact cooling

Cooling Continuous contact cooling (not adjustable)

It comes with SkinIntel for skin phototype. It has three optional laser handpieces: 2940 fractional ablative laser, 1540 fractional non-ablative, 1064+ laser handpiece Advanced contact cooling that maintains constant 5° temperature during treatments Advanced Fluorescence Technology (AFT), pulsed UVB for hypopigmentation. The platform can be equipped with a long-pulsed Nd:YAG 1064 nm, fractional q-switched 1064 nm, and fractional 1540 and 2940 nm laser under different trademark names such as ClearSkin, ClearLift, etc.

Features The workstation can be equipped with longpulsed Nd:YAG1064 nm, 1550 nm, and 1940 nm lasers and five IPL handpieces for a wide range of applications

a

According to Candela, the SWT is a narrowband technology defined by dual filters and sub-­millisecond pulses. Table 2.6 lists the Nordlys system specification. The system has eight Ellipse IPL handpieces and Frax 1550, Frax 1940, and Nd:YAG 1064 nm with different indications, as shown in Table 2.7 b According to Cynosure, the SmoothPulse™ technology avoids energy spikes often used by competing systems to deliver treatment—patient skin stays cooler and more comfortable without sacrificing efficacy. Full technical specification for Cynosure Icon is listed in Fig. 2.4a, and the light spectrum of the Max G handpiece in Fig. 2.4b c The new platform has several IPL handpieces such as Dye VL PRO 450–600 nm Cooled Applicator, Dye VL 500-600 nm Cooled Applicator in a stationary and in-motion mode, Cooled VL-PL 540 nm Applicator, and Cooled and non-cooled SR 570 nm Applicator [17]. According to Alma, Advanced Fluorescence Technology (AFT) is the new generation of IPL that enables continuous square-shaped pulsing with moderate peak power throughout the entire pulse. However, a 2007 study did not show a significant difference in results between Lumenis and Harmony IPL [18]. The full technical specification for Alma Harmony XL Pro is listed in Table 2.8

Harmony All handpieces are equipped Alma with a dual cutoff to eliminate light over 950 nm, as shown in Fig. 2.4dc

Pulse width Filter technology (ms) ® SWT (Selective Waveband 0.5–99.5 Technology)a, which means that all filters are dual cutoff to eliminate light over 950 nm, as shown in Fig. 2.4a Icon MaxG is the only filter with a 1–100 Palomar dual cutoff, as shown in cynosure Fig. 2.4b SmoothPulse™ b

System name Nordlys Ellipse Candela

Table 2.5  Comparison of different IPL systems with interchangeable handpieces

48 2  Laser and Intense Pulsed Light

IPL

49

a

MaxG Wavelength: 500670 nm and 8701200 nm Pulse width: 1-100 msec Spot size: 10 x 15 mm Energy: Up to 80 J/cm2

MaxR Wavelength: 650-1200 nm Pulse width: 1-100 msec Spot size: 16 x 46 mm Energy: Up to 46 J/cm2

MaxRs Wavelength: 650-1200 nm Pulse width: 1-100 msec Spot size: 12 x 28 mm Energy: Up to 70 J/cm2

Fig. 2.4 (a) Characteristic of different Icon Palomar in terms of size, light spectrum, fluence range, and application. (b) Light spectrum of the Max G handpiece that balances the affinity between melanin and hemoglobin to induce photothermolysis equally in both chromophores

50

2  Laser and Intense Pulsed Light

b

MaxYs Wavelength: 525-1200 nm Pulse width: 1-100 msec Spot size: 18 x 28 mm Energy: Up to 81 J/cm2

2940 fractional ablative laser Wavelength: 2940 nm Treatment zone-fractional: 10 x 10, 6 x 6 mm Flatbeam: 6 x 6 mm Microbeam density: Up to 1000 cm2 Pulse width: 0.25-5 msec Max. repetition rate: Up to 6 Hz

60

Filtered Out Light

100

40

10

20

1

0

500

700

800

Wavelength, nm

Fig. 2.4 (continued)

0.1 1000

Absorbtion coefficient, cm–1

Spectral fluence J/(cm2/µm)

80

IPL

51

Table 2.6  Nordlys applicator specifications

Table 2.1: NORDLYS APPLICATOR SPECIFICATIONS ELLIPSE IPL Type/Wavelength Band Fluence Range Pulse Time Pulse Delay Number of Pulses Duration of Pulse Train Spot Size

HRD 645 (645-950 nm) HR/HRL 600 (600-950 nm) VL/VLS 555 (555-950 nm)

PR/PRS 530 (530-750 nm) PL 400 (400-720 nm)

2-26 J/cm2 0.5-99.5 msec (depending on applicator) 1.5-99.55 msec 1-4 0.5-700 msec HR 600, HRD 645, VL 555, PR 530, PL 400 10 mm x 48 mm

HRL 600 18 mm x 48 mm

FRAX 1550 Laser 1550 nm Wavelength

VLS 555, PRS 530 Hexagonal: 90 mm2

ND:YAG 1064 1064 nm

Fluence Range/ 5-100 mJ Energy

20-500 J/cm2 6-40 J/cm2 (onychomycosis)

Pulse Duration

1-20 msec

2.5-90 msec 0.3-0.9 msec (onychomycosis)

4-12 mm

1.5-5.0 mm

Scan Width/ Spot Sizes Skin Cooling

SoftCoolTM Integrated Air Cooling

2  Laser and Intense Pulsed Light

52

Table 2.7  List of indications for Nordlys different handpieces HR (600–950) HDR Nd:YAG PR (530–950) (645–950) Frax 1550 Frax 1940 1064 nm PL 400 VL (555–950) Telangiectasias Permanent Leg vessels Benign Skin resurfacing Skin Port-wine stains hair (0.1–3 mm epidermal resurfacing Coagulation of soft reduction Benign pigmented in Coagulation tissue lesions (e.g., pigmented diameter) of soft tissue Benign pigmented lesions solar lesions, including but Benign Benign vascular lentigines) vascular not limited to lesions (e.g., lesions lentigines (age diffuse redness) Port-wine spots), solar Rosacea lentigines (sunspots), stains Poikiloderma of Venous and ephelides Civatte lakes (freckles) for Inflammatory Fitzpatrick skin types Epidermal acne vulgaris pigmented I–IV (PR 530) lesions Table 2.8  Harmony XL pro system specifications Spot size Light Wavelength Module source (cm2) (nm) Cooled IPL Module 5 cm2 spot size SHR Pro Flash 5 650–950 (5) cooled lamp

Mode HR SHR

Cooled IPL Module 3 cm2 spot size SVL Flash 3 515–950 cooled lamp VL/PL Flash 3 440–950 cooled lamp SR cooled Flash 3 570–950 lamp Dye-SR Flash 3 550–650 Pro lamp

Dye VL-Pro

Flash lamp

SHR Pro Flash (3) cooled lamp

3

3

450–600

650–950

Pulse widths/ timers

Pulse repetition rate (Hz)

Energy density (J/ cm2)

30, 40, 50 ms Timer: 1, 3, 30 s

1/2

5–20

3

3–7

2/3

5-30

2/3

5–30

2/3

5–30

1/2

Up to 14

3

1–4

1/2

Up to 15

3

1–4

1/2

5–25

3

3–7

10, 12, 15 ms 10, 12, 15 ms 10, 12, 15 ms Dye-SR 10, 12, 15 ms Dye-­ Timer: 1,3, SSR 30 s Dye-VL 10, 12, 15 ms Dye-­ Timer: 1,3, SVL 30 s HR 30, 40, 50 ms SHR Timer: 1,3,30 s

(continued)

IPL

53

Table 2.8 (continued) Spot size Light Wavelength Module source (cm2) (nm) SSR Flash 3 540–950 cooled lamp SST Flash 3 780–950 cooled lamp Non-cooled IPL Module 6.4 cm2 spot size SVL Flash 6.4 515–950 lamp VL/PL Flash 6.4 440–950 lamp SR Flash 6.4 570–950 lamp HR Flash 6.4 650–950 lamp ST Flash 6.4 780–950 lamp Acne Flash 6.4 420–950 lamp

Mode

Acne S-Acne

Module Technology Laser Nd:YAG cooled module Nd:YAG Cooled long pulse 1064 nm Nd:YAG

Pulse widths/ timers Timer: 1,3,30 s Timer: 1,3,30 s

Pulse repetition rate (Hz) 2

Energy density (J/ cm2) 1–15

5

0.5–3.5

10, 12, 15 ms 10, 12, 15 ms 10, 12, 15 ms 30, 40, 50 ms Timer: 10,30,90 s 30, 40, 50 ms 2 ms

2/3

5–25

2/3

5–25

2/3

5–25

1/2

5–25

2

1–7

1/2

5–25

10

0.3–1.2

Wavelength (nm)

Spot size (mm)

Pulse width

Pulse frequency (Hz)

1064

2

10 ms

1

6

15, 45, 1 60 ms 15 ms 1

10

Cooled long pulse 1320 nm Nd:YAG

Nd:YAG

1320

Laser Nd:YAG non-cooled module Q-Switched 1064 Q-Switched Nd:YAG 1064 nm 1064 Nd:YAG 532 High Power Q-Switched 1064 nm Nd:YAG

Q-Switched Nd:YAG

1064 1064 532 1064 1064

5 × 5 Pixel 10 ms 1 6 30, 40, 1 50 ms 5 × 5 Pixel 30, 40, 1 50 ms 1,2,3,4,5,6 5 × 5 Pixel 2, 3, 4 KTP 1,2,3,4,5,6 5 × 5 Pixel 2,3,4 mm KTP 5 × 5 roller 7 × 1 roller

Energy density/ fluence/ depth 30–450 J/ cm2 30–150 J/ cm2 20–50 J/ cm2 3–25 J/cm2 5–40 J/cm2 1–11 J/cm2

20 ns 20 ns 20 ns

1, 2, 4 1, 2, 4 1, 2, 4

600–1200 mJ/p

20 ns 20 ns 20 ns

1, 2, 4 1, 2, 4 1, 2, 4

600–1200 mJ/p

20 ns

N/A

54

2  Laser and Intense Pulsed Light

Cleanse

Purify

A special treatment tip usesvacuum to gently lift acne impurities helping extract dirt, blackheads, dead cells and excess oil from the pores.

Broadband light is applied helping to destroy acne causing bacteria and to reduce sebum production.

Replenish

With profusion technology. vacuum gently stretches the skin cells, allowing the application at topical products into the intercellular spaces in the skin.

The vacuum is released, having helped enhance topical product application for improved overall treatment outcomes.

Fig. 2.5  Mechanism of action of Isolaz IPL from Solta

Special IPL Some IPL systems provide some extra features. For example, Isolaz from Solta has negative pneumonic pressure (vacuum) for acne [19] as shown in Fig.  2.5, or Lumecca from Inmode has higher energy on a specific light band (higher in the 500–600 nm range) to target vascular and pigmented lesions specifically [20].

Lasers Laser systems, as previously stated, produce a single wavelength of light in parallel rays [21]. The light source determines the wavelength of a laser; one light source can produce more than one laser wavelength using different frequency conversion technologies [22]. For example, a neodymium-doped yttrium aluminum garnet crystal (Nd:YAG) can be used for 1064 nm and 532 nm lasers by doubling the frequency using a potassium titanyl phosphate (KTP) crystal [23]. As discussed in Chap. 1, all lasers are available in different pulse widths: • • • •

Long pulses ranging from 0.45 to 400 ms. Quasi-long pulses typically last around 300 s (0.3 ms). A short pulse, typically lasting 5 ms (0.005 s) and referred to as Q-switch. An ultrashort pulse with a duration of 300 to 500 ps (0.5 ns). Many authors have discussed the shortcomings of picosecond lasers, describing them as not true picosecond lasers, claiming “further development of this technology is warranted” [24].

Color Sensitive These lasers have high absorption coefficients for colored chromophores, including hemoglobin (and its derivative) and melanin. The higher a laser’s absorption coefficient toward a chromophore, the greater the absorption and photothermolysis effect, which has pros and cons. When compared to color-blind lasers, these have

Lasers

55

relatively shorter wavelengths. Here is a list of the most frequently employed wavelengths in the aesthetic and dermatology fields, from short to long: • 532 nm is available in long, short, and ultrashort pulse widths. This laser, also known as the green laser, is made by doubling the 1064 nm Nd:YAG laser using a KTP medium [25]. Therefore, practitioners might notice that 532  nm and 1064 nm lasers are standard on all Q-switched laser devices. Because of its high hemoglobin absorption and shallow skin penetration, the KTP 532 nm laser is primarily used to treat vascular lesions such as erythema, telangiectasia, and some superficial pigmentation lesion [26, 27]. • 585 and 595 nm pulsed dye lasers have wavelengths of 585–595 nm and a high absorption coefficient for oxyhemoglobin and deoxyhemoglobin [28]. Therefore, these are mainly used for vascular, pigmentation, and keloid scars [29, 30]. Pulsed dye lasers are available in long and short pulse ranges [31, 32]. • 694 nm ruby laser is not frequently used in the aesthetic field. • 755 nm alexandrite is a versatile laser that is also known as the Alex laser. Several indications vary depending on the pulse width in long, quasi-long, short, and ultrashort. The long-pulsed Alex laser is mostly known for its indication in laser hair removal (LHR) in skin types I, II, and III. • Diode laser (805 nm, 808 nm, 810 nm) is available as high and low fluences in long pulse and is mainly indicated for LHR [33, 34]. It is worth noting that some devices generate diode wavelengths from the Nd:YAG medium, and some laser devices emit three different lasers (755 nm, 810 nm, and 1064 nm) simultaneously within the same pulse [35, 36]. • 1064 nm Nd:YAG laser is the most versatile laser available in long, quasi-long, short, and ultrashort pulses. This is due to the 1064  nm laser’s moderate and equal absorption coefficient for melanin and hemoglobin [37]. The YAG laser is the gold standard for LHR and vascular lesions in long pulses, especially in darker skin types (IV and V) [38]. This laser is frequently used for pigmentation and skin rejuvenation in short and ultrashort pulses [39, 40] (Fig. 2.6). –– This video discusses optimizing the YAG laser parameters for hair removal application. https://drive.google.com/file/d/1IW-FQO8mNYyHlTTUlf2v7S0 OE_BZgFhf/view?usp=share_link –– This video discusses optimizing the Yag parameters for Laser vein removal. https://drive.google.com/file/d/14wYF8em9BKTj3zQrK_oOrUO3FEyB-­ Mmf/view?usp=share_link –– This video discusses optimizing the Yag Laser parameters to target superficial vascular lesions. https://drive.google.com/file/d/1JzNlu2NUwbUB8NOfk15 Qs7JIRxR5afEm/view?usp=share_link

Color-Blind These lasers, such as water molecules, are absorbed by transparent chromophores in the skin and have little affinity for colored chromophores. As a result, skin type has less of an impact on choosing laser settings, and darker skin types are considered

56

2  Laser and Intense Pulsed Light

1000

532

755

1064

Absorption coefficient, cm–1

Melanin Hb02 Hb 100

10

1 500

600

700

800

900

1000

1100

Wavelength, nm

Fig. 2.6  Absorption coefficients of melanin and hemoglobin at 532 nm, 755 nm, and 1064 nm lasers

safer to be treated with these lasers. Color-blind lasers work by ablation (ablative lasers) and coagulation (non-ablative) or a combination of both [41, 42]. Ablative lasers have a longer wavelength and, thus, a higher water absorption coefficient. As a result, ablation refers to the process by which skin tissues vaporize due to an aggressive photothermolysis process. Furthermore, ablative lasers have relatively shallow penetration (max of 400 μm). Coagulation, on the other hand, refers to producing an effect by heating the treatment area to a clinical point to induce protein coagulation, followed by skin rejuvenation, with little to no ablation effect. Non-ablative fractional lasers work by performing thermal micro-coagulation columns in the dermis. The collagen is denatured, which promotes regeneration and results in skin smoothing and rejuvenation [43]. As the wavelength of a laser increases, so does its affinity for water; as a result, lasers perform more ablation and less coagulation. These lasers are mainly delivered in fractional mode, as the laser beam is delivered in small beams called microthermal treatment zones (MTZs). As illustrated in Fig. 2.7, fractional lasers can leave untreated areas intact, which act as reservoirs [44]. As a result, fractional lasers are safer and have a shorter downtime and recovery time than non-fractional ones. This concept will be covered in greater depth in a later chapter. • 1320 nm Nd:YAG in long pulse • 1450 nm diode lasers in long pulse • 1540 nm, 1550 nm, and 1560 nm Er:Glass lasers are non-ablative, mostly fractional, and commonly referred to as fractional non-ablative lasers (FNAL). These lasers have a nearly pure coagulation effect and can penetrate to 1.4 mm depth. • The 1927 nm thulium laser has an excellent balance of ablative and coagulative effects. This laser has a penetration depth of 400 microns. • The 2940 nm Er:YAG laser used to be available only in long pulses (1–2 ms), and because of its purely ablative nature, Er:YAG is commonly referred to as the cold

Lasers

57 Nonfractional

Fractional

Fig. 2.7  Difference between the non-fraction laser (left) and fractional (right). The untreated areas between the MTZ work as a source for stem cells to shorten the recovery time

laser. However, a newer system provides variable square pulse (VSP) between 175 and 800 s, greatly increasing its indications. • The 10,600  nm CO2 laser is the most studied ablative laser [45]. Most CO2 lasers can generate a high peak pulse (super pulse) in the 200–800 μs range, with lesion depths ranging from 200 to 650 μm according to the energy used (5 to 30 mJ) [45, 46]. All ablative lasers have an intrinsic ablation and coagulation ratio. The fluence controls the ablation depth, but the coagulation/ablation ratio for the same wavelength and fluence can be controlled by changing the pulse width. Figure 2.8 shows how increasing the pulse width increases coagulation. Some lasers, such as Er-YAG, can provide a pure ablation effect with minimal coagulation when used in short pulse width. This is known as cold ablation. All ablative lasers generally show intrinsic ablation and coagulation ratio [47]. The fluence controls the ablation depth, but the coagulation/ablation ratio for the same wavelength and fluence can be controlled by changing the pulse width; the coagulation increases by increasing the pulse width [48], as shown in Fig. 2.8. When used in short pulse width, some lasers, such as Er-YAG, can provide a pure ablation effect with minimal coagulation, known as cold ablation [49]. A longer pulse width would result in a more noticeable coagulation effect, making the treatment warmer [9]. This section discusses the available laser platforms and devices according to wavelength, pulse width, and special features. We will discuss each one of these indications explicitly in a separate chapter. The same laser wavelength might be used for different indications by adjusting other settings such as fluence and spot size. Most standard laser devices emit laser light in three modes: long, short, or ultrashort. Nonetheless, practitioners can customize two or more modules with different emission modes with the new modular. SharpLight’s OmniMax S4, for example, offers a 1064 nm Nd:YAG laser in both long (ms) and short (Q-switch ns) pulse

58

2  Laser and Intense Pulsed Light Long laser pulse

Time Hot Ablation

Medium Laser pulse

Short laser pulse

Time Warm Ablation

Time Cold Ablation

Fig. 2.8  Effect of pulse width on the coagulation/ablation effect for an ablative laser

modes. Some devices, such as the Lutronic PicoPlus, provide Nd:YAG laser in both shot and ultrashort modes.

Color Sensitive According to Pulse Width Long Millisecond (ms) and Quasi-long Microsecond (μs) Laser Because of the long pulse width, these lasers are effective on relatively large targets such as hair follicles and blood vessels (between 30 and 100 μm). These targets’ long thermal relaxation time (few ms) allows for efficient heat buildup and a clinical temperature target [50]. Because of the short relaxation time, these lasers cannot be used to target small targets like melanosomes, and miniature vessels will cool down quickly as they pass heat to surrounding tissues. 532 nm KTP Melanin and hemoglobin absorption coefficients are 555 and 235 cm−1, respectively [51]. The low ratio of 2.4:1 indicates that the two chromophores compete with each other and have low selectivity. As a result, this laser should be used with caution in skin type III and avoided in skin types IV and above. As a result, the 532 nm laser is always used in conjunction with the 1064 nm laser on the same platform because they share the same light source; the 532 nm laser is created by passing a 1064 nm laser through a KTP crystal to double the frequency [52]. Because of the high melanin absorption in higher skin types, the use of 532 nm in long pulse mode is limited to skin types I–II. Long-pulsed 532 nm laser is used to treat superficial, small, and pink and purple veins, facial telangiectasia, and diffused redness [53]. It also treats new scar redness (erythema), port-wine stain

Lasers

59

(PWS), hyperpigmentation, and small warts in skin types I and II [54]. In our opinion, the use of this laser in the aesthetic field is limited, but it is more widely used in dermatology settings. To our knowledge, two platforms offer the 532 nm laser in ms pulse width range, the excel V+ from Cutera, and Light C from Quanta. This is the last laser a practitioner would add to their aesthetic practice. Comparison Table 2.9 compares two long-pulsed 532 nm laser systems. excel V Interface Figure 2.9 shows the interface of excel V and the function reported by the user manual [55]. 1. The fluence is the amount of energy measured in J/cm2. To make changes, use the Up/Down arrows. 2. The duration of each pulse is measured in milliseconds (ms). To make changes, use the Up/Down arrows. When using the Genesis V handpiece, the pulse duration is fixed at 0.3 ms and cannot be changed. 3. The repetition rate is the number of pulses per second measured in Hz with the foot pedal depressed. To make changes, use the Up/Down arrows. 4. By selecting the Temperature icon, you can set the temperature to 5°C, 10°C, 15°C, or 20°C. The current temperature is also shown. When using the Genesis V handpiece, the temperature cannot be adjusted. 5. For common indications, the Memory button saves three different settings per wavelength. 6. The number of pulses is shown. To reset, press the reset button. 7. The spot size can be adjusted from 2 to 12 mm. To make changes, use −/+. The spot size cannot be changed when using the Genesis V handpiece. 8. Toggle between Standby and Ready mode by pressing the Standby/Ready button. When in Standby mode, the Standby/Ready button is yellow, and the handpiece cannot be fired. When in Ready mode, the Standby/Ready button turns green. Unless the handpiece is removed from the holster, the system will not Table 2.9  Comparison of two long-pulsed 532 nm laser systems System name Excel V+ from Cutera Light C from Quanta

Spot size 2 to 12 mm

Pulse width Up to 25 ms

up to 6 mm

Up to 25 ms

Max fluence Handpiece 25 J/cm2 Cool view with contact adjustable cooling 12.5 J/ Contact and air cm2 cooling integrated with the handpiece

Features The platform is integrated with short- and long-pulsed 1064 nm (Genesis VTM)a The platform is integrated with long- and short-pulsed 1064

The Genesis VTM handpiece delivers 532 or 1064 nm Nd:YAG laser light in micro-pulses that gently and safely target microvasculature to accelerate the process of collagen production, therefore improving the look of wrinkles and other visible indications of aging a

60

2  Laser and Intense Pulsed Light

Fig. 2.9  excel V interface. The functions are numbered as follows: (1) The user can adjust fluence control depending on the condition being treated. (2) Pulse duration control: the operator should choose a shorter pulse duration with smaller targets. (3) Repetition rate: the operator should choose the repetition rate of laser shots based on their experience and comfort with moving the handpiece. (4) The contact cooling device’s temperature. (5) Memory: the user’s preferred settings can be saved. (6) The number of shots required in the current treatment. (7) Spot size in millimeters: the size of the spot is related to the lens aperture, which can be adjusted depending on the depth of the target. (8) Ready/standby switch. (9) Setting the wavelength

enter Ready mode. After the “flute” sound indicates that the system is ready, press the foot pedal to begin the pulse. 9. Wavelength—the wavelength selected will be displayed. To choose a wavelength for treatment, choose either 532 nm or 1064 nm. When using the Genesis V handpiece, the wavelength cannot be adjusted. 10. Screen of information—the Information & Adjustment screen can be accessed to check the system software version or to change the screen brightness, volume level, or beam intensity. 585 and 595 nm Pulsed Dye Lasers (PDL) The longer wavelength pulsed dye lasers make it safer than 532 nm because they penetrate deeper and have less affinity for melanin in the epidermis. PDL lasers’ indications include all 532 nm, exceeding them to include inflammatory acne, photorejuvenation, and rosacea [29, 56]. Furthermore, it can be used with other lasers to treat keloid scars, melasma, and other dyschromia lesions [29, 57]. 595 nm wavelength replaced 585 nm in the aesthetic field to increase the penetration depth in large-sized blood vessels or vessels at the dermis. Some studies showed that the 585 nm wavelength is superior in treating vascular lesions, such as port-­ wine stains [58]. According to the parameters and mechanism of action, PDL treatment can be classified as purpuric or non-purpuric [59]; the traditional high fluence and short pulse width cause blood vessel rupture and possibly bruising. The new systems can slowly heat the targeted blood vessels and include blood coagulation instead of rupturing the blood vessels [60], as shown in Fig. 2.10.

Lasers

61

Fig. 2.10 Difference between the pulse width of purpuric (0.45 ms) and non-purpuric (40 ms) pulsed dye laser

Comparison Table 2.10 compares two long-pulsed 532 nm laser systems. Vbeam from Candela is the main commercial PDL in the ms range in North America. The system has been recently updated from Perfecta to Prima. The new Prima has a larger collimated handpiece (up to 15 mm) and an additional cooling method. Both models have a special compression handpiece for pigmentation; this pigmentation handpiece is fitted with a special lens to reduce the blood flow in the treatment area (less oxyhemoglobin competition). The handpiece is available in 7 and 10 mm. Table 2.11 compares the Vbeam Perfecta and Prima in terms of spot size, pulse width, maximum energy, and other features. The long-pulsed dye laser is an excellent addition for an advanced aesthetic practitioner. It can, however, be easily replaced with a versatile Nd:YAG system, which is a cornerstone of any aesthetic practice. Vbeam Interface Figure 2.11a shows the interface of the Vbeam as provided by its user manual [61]. There are five main applications: telangiectasia, photorejuvenation, angiomas, port-­ wine stains, and warts. Each main application has a submenu with several applications with suggested settings. However, the operator can override these settings, as shown in Fig. 2.11b, which represents the interface of the Vbeam. The operator can see the similarity between Figs. 2.9 and 2.11b as the operator has to deal with the same concepts when operating any laser machine.

62

2  Laser and Intense Pulsed Light

Table 2.10  Comparison of two long-pulsed 532 nm laser systems Max fluence Pulse at System name Spot size width 12 mm Vbeam from Up to 15 mm 0.45 8 J/cm2 Candela to 40 ms

CYNERGY from Cynosure

Up to 12 mm 0.5 to 7 J/cm2 with an 40 ms additional 15 mm handpiece

Handpiece Cryogen spray with additional contact cooling method Stand-alone forced-chilled air

Features It has an additional 1064 nm Nd:YAG laser

It has an additional 1064 nm Nd:YAG laser. Both wavelengths are emitted sequentially—pulsed dye first and then Nd:YAG—with a configurable delay for improved energy absorption

Table 2.11  Vbeam Perfecta and Prima comparison Spot size Up to 12 Up to 15

Name/maker Vbeam Perfecta from Candela Vbeam Prima

Pulse width 0.45–40 ms 0.45–40 ms

Max energy 8 J

Additional wavelength NA

12 J

1064 nm

Features Cryogen spray cooling system only Additional contact cooling method

a

Submenu

Applications menu bar

Treatment applications

Needs calibration

Applications Telangiectasia

Pulse Duration

Photorejuvenation

Diffuse redness

Angiomas

Wrinkles

Port wine stains

Pigmented lesions

7PL

10PL

Warts

Dyschromia

7PL

10PL

7

10

7

12

10

Miscellaneous

3x10

3

5

7

10

12

7PL

10PL

Fig. 2.11 (a) Main treatment applications of Vbeam with its submenu. (b) Operator interface of the Vbeam laser machine, in which they can adjust treatment settings to customize the treatment according to the client’s condition

63

Lasers

b

System status bar Ready/standby button and system status symbol Calibration button System status Screen lock button

System settings menu button Applications menu bar

Needs calibration Applications Fluence

Pulse Duration

10ms

J/cm2

8.25

Cooling

3x10

5

3

7

10

12

7PL

Pulse count

10PL

Active spot size identification bar Fluence select buttons Pulse Duration select buttons Cooling Button Cooling menu button Treatment pulse counter and reset button Treatment summary button

Fig. 2.11 (continued)

755 nm Alexandrite (Alex) Laser The Alex laser’s absorption coefficient is 163 and 3 cm−1 for melanin and oxyhemoglobin, respectively [37]. The ratio is 54:1, making Alex the most selective melanin laser. As a result of melanin’s high absorbance and selectivity, the long-pulsed Alex laser is the treatment of choice for laser hair removal (LHR) and benign superficial

64

2  Laser and Intense Pulsed Light

Fig. 2.12  New concept of using a blend of two different wavelengths, 755 and 1064 nm lasers, to target hair follicles at two different depths

pigmentation in skin types I–III [62]. However, the high melanin absorption makes it less suitable for skin type IV [63]. Nonetheless, practitioners can still use the Alex on skin type IV, with more conservative settings (large spot size, low fluence, and long pulse width). Most platforms provide 755 nm and also a 1064 nm laser, known as a dual-wavelength LHR workstation. The 755/1064  nm laser devices are the foundation for practitioners who want to begin with simple aesthetic indications like LHR in skin types I to IV. These platforms, however, are bulky and heavy (200–300 LB) and may require an external cooling device. New hybrid systems, such as SPLENDOR X from Lumenis and Duetto MT EVO from Quanta, can be synchronized to be fired at both 755 and 1064 nm wavelengths individually or simultaneously, as shown in Fig. 2.12 [64]. It is important to note that unlike the Alma Soprano series, these two systems have two separate laser sources. On the other hand, the Soprano series uses a modified Diode laser source for the 755, 810, and 1064 nm lasers. Comparison Table 2.12 compares five 755 nm laser systems in terms of available wavelength, cooling mechanism, operation interface, maximum energy, pulse width, and spot size.

755 nm

Cryogen spray Digital LCD, intuitive, and user-friendly DMC™ (Dry Digital LCD, Molecular intuitive, and spray Cooling) user-friendly Contact or LCD forced air Cryogen spray Digital LCD, and forced air intuitive, and user-friendly

Forced air

Mono-­color, non-­intuitive Digital LCD, intuitive, and user-friendly Mono-­color, non-­intuitive

Interface

0.6 ms to 1s

0.35–300 ms

2-100 ms

0.5–100 ms 0.5–300 ms

Pulse with

Up to 30 mm

Up to 18 mm

Up to 16 mm

Up to 24 mm Up to 24 mm

Spot size

2–100 ms Up to 16 mm 55 J Alex, 3-100 20 × 20 mm, 80 J Nd:YAG 24 × 24 mm square

53 J Alex, 79.2 J Nd:YAG 53 J Alex, 79.2 J Nd:YAG 100 J Alex

70 J Alex

45 J Alex, 63 J Nd:YAG 45 J Alex, 63 J Nd:YAG

Energy

The practitioner can configure the platform to add IPL, 1064 nm, 2940 nm, and 1320 nm Simultaneous Alex-Nd:YAG hybrid laser shots, integrated smoke evacuate technology, square and round treatment area for easy treatment

Scanner for large areas (add-on), avalanche effectb, DMC™ (Dry Spray Molecular Cooling) c

Scanner for large areas (add-on), special burst mode (each laser pulse is split up into several short, quick sub-pulsesb. The skin surface can cool down between the sub-pulses The risk of side effects is minimized), and does not require gel Cryogen spray needs to replace the cryogen canister

No consumables, equipped with Skintel Melanin Reader

No consumables

Features

a

This video shows the Elite+ from Cynosure and discusses different treatment parameters. https://drive.google.com/ file/d/1knB1X9HEtWmqW5m0FO2jvFCv3VNJ8HHw/view?usp=share_link b It has recently been claimed that delivering laser in successive pulses allows hair follicles to absorb it more efficiently. Following each laser pulse, there was increased laser absorption at the hair follicles level, known as the avalanche effect or stacking. The new hair removal technology involves sending a series of laser pulses to the same skin area while optimizing the laser pulse parameters for maximum avalanche impact. This method differs from a standard “stamping” technique in which the laser handpiece is moved from spot to spot across the treated skin with no overlap, and single high-fluence pulses are delivered to each location [65, 66] c A non-contact cooling method that uses dry water mist rather than cryogen to avoid epidermal injury caused by excessive freezing

Light A 755 Quanta SPLENDOR X Combo, Lumenis hybrid

AvalancheLase Combo Fotona

GentleMax Pro Combo Candela

Arion Alma

Combo

Forced air as a separate unit Forced air as a separate unit

Combo

Elite+ Cynosure Elite iQ Cynosure

a

Emission Cooling

Name/maker

Table 2.12  Comparison between different laser systems that have Alex lasers

Lasers 65

66

2  Laser and Intense Pulsed Light

GentleMax Figure 2.13a shows the GentleMax interface as shown in their clinical manual [67]. The GentleMax and GentleMax Pro interfaces are more user-friendly and interactive compared to the Cynosure Elite+ (Cynosure Elite iQ was released by Cynosure at the time of writing the book). As discussed, the laser machine could suggest settings according to skin type, tanning condition, hair color, and thickness. Once the operator inputs the information, the system will take you to the operator interface shown in Fig. 2.13b. At this stage, the operator can adjust the treatment setting and individualize it accordingly. The GentleMax series is equipped with a dynamic cooling device (DCD) that uses a cryogen spurt to cool the epidermis during the procedure. The integrated cooling device has three important timing inputs. Pre is the spurt duration before the laser shot in ms. After the Pre-spurt, there is a delay time associated with the laser shot; then the Post-spurt after the laser shot [68]. Some reports about hyperpigmentation are associated with laser hair removal due to CDC malfunction, as shown in Fig. 2.13c [69]. a Standby Alex Appications

755nm

Hair Removal: Select Parameters Skin

Hair

Fitzpatrick Type

1.5

3

TAN

Color

Thickness

I

IV

No Tan

Light

Fine

II

IV

Active

Medium

Medium

III

VI

Established

Dark

Coarse

6

8

10

12

15

18

Fig. 2.13 (a) Main interface window of GentleMax in hair removal treatment. The settings depend on four factors; two factors are related to the skin, and the others are related to the hair. (b) Operator interface window. In this window, the operator can change the pulse width (duration), the firing rate, the fluence, and the cryogen cooling. (c) Several ring-shaped brown hyperpigmentations on the cheek 2 weeks following 1450 nm diode laser treatment with a DCD [69]

Lasers

67

b

Ready/Standby Button System status messages Cooling spray settings System laser/Guided mode select Applications menu bar

Standby

Alex Appications Fluence controls/ indicator

755nm

Fluence

Cooling Pre Delay

0

Post

Alex

0.25

300

3

Pulse duration control

6

Pulse count

Single

0.25 ms

1.5

Press to select

Rate

Duration

8

10

S

12

Spot size Identifier Bar

1

15

0 10

18

Cryogen purge

Calibrate button Cryogen canister status

Reports button

Repetition rate select

c

Fig. 2.13 (continued)

Pulse count & reset

System settings menu

68

2  Laser and Intense Pulsed Light

Diode Laser The intermediate absorption of the diode laser by melanin and low absorption by oxyhemoglobin positioned it as the gold standard in LHR. Consequently, the diode laser is mainly used in LHR but still has other indications, such as benign superficial pigmentation and photorejuvenation [70]. Systems offer this wavelength alone or in combination with other wavelengths, such as 755 and 1064 [36]. Similar to what we discussed in the IPL section, there are two treatment modes of LHR with diode static and dynamic. High-Fluence Static Mode The platforms rely on the same traditional “selective photothermolysis” and its bystander concept as it delivers a high fluence pulse to “zap” the hair strand. Practitioners should select the appropriate parameters according to skin phototype and hair texture. The LightSheer Duet from Lumenis has an extra negative pneumatic handpiece HS that creates a vacuum, as shown in Fig. 2.14. When the handpiece is placed on the treatment area, it creates suction that draws the skin closer to the treatment handpiece, reducing stray light while increasing the therapeutic

Fig. 2.14  Operator interface window for the LightSheer pneumatic handpiece HS. In this window, the operator can change the vacuum settings

Lasers

69

effectiveness. Therefore, the treatment parameters are significantly lower than the standard handpiece ET, shown in Fig. 2.15 [71]. Another example of the static diode laser is Vectus from Cynosure. LightSheer HS Vacuum Handpiece The “No. pulses” indicates the number of consequent pulses the handpiece provides each time it is triggered. The number shown under the number of pulses (500) in Fig. 2.15 indicates the actual pulse interval between pulses and ranges from 333 to 2000 ms. Within this time, the area is under vacuum and irradiated with laser in 1, 2, or 3 pulses. ET Standard Handpiece Similar to other platforms, The LightSheer Duet from Lumenis has recommended setting according to the skin type, hair color, and texture, as seen in Fig. 2.15a and b. Figure 2.15b shows the treatment screen, where the operator can manually adjust the treatment parameter. When the OptiPulse is sent on auto, the system will choose the suitable pulse width for a given fluence. a

Clinical indications screen for ET handpiece Clinical Indications

Select the skin type

Skin Type:

Select the hair color

Hair color:

Select the hair texture

Load Physician recommended presets

Hair Texture:

L

I

II

Blond/Red

III

IV

Light Brown

Fine

Dark Brown

Coarse

Fast

Black

Dense

Treatment parameters OptiPulse Auto Fluence Rate (Hz)

VI

V

ChillTip

OK

40 j/cm2 On

Cancel

Load use presets Presets for currently selected clinical indications

Fig. 2.15 (a) Clinical indications interface. The operator can use the suggested treatment parameters by feeding his input in the clinical indications interface window. (b) Operator interface window. The operator can override the suggested treatment parameters by manually changing the rate, OptiPulse (pulse width), and fluence

70

2  Laser and Intense Pulsed Light

b

ET Handpiece Treatment Screen After you have selected the ET handpiece on the startup screen and calibration is completed, the ET handpiece treatment screen is displayed. Load user presets

Save user presets

Load physician Recommended presets

Current clinical settings Cllinical indications

Clinical indications screen selector

M

Skin Type: 1 Hair color: Blond Red Hari texture: Fine

L Rate (Hc)

Opti pulse (ms)

Fast

Auto

Med

30

Slow

100

3.00 Hz

400

Fluence (j/cm2) 00

Pulse rate field

OptiPulseTM mode

Fluence bar Fluence j/cm2

40 -

Increase fluence

+ 10

1000 Check TIP

Fluence field

Decrease fluence

0000

0

000000

Standby

Ready

Toggle chill tip on/off

ET handpiece treatment screen

Fig. 2.15 (continued)

Vectus Cynosure Vectus is another static diode LHR platform from Cynosure with new photon-­ recycling technology [72]. Figure 2.16 shows the clinical indication interface window for Cynosure Vectus. The settings suggested by the platform depend on four factors; one is related to the skin (skin type), and the other three are related to the hair (diameter, density, and color). We will learn more about identifying these factors in Chap. 3. Low-Fluence Dynamic Super Hair Removal (SHR) These platforms are new and use multiple passes of low-level fluence laser. Instead of zapping the targeted hair follicle with one pulse of laser to induce thermolysis, this diode laser induces incipient necrosis and perifollicular edema via a high repetition rate of short pulses to build up the heat gradually, as shown in Fig. 2.17 [73]. The gradual heat buildup in the dermis damages the hair follicles and prevents regrowth while shunning injury to the surrounding tissue. This approach significantly decreases the treatment discomfort by delivering average high energy over a large area (10 × 10 cm2) by continuously moving the handpiece over the treatment area (multiple passes or inmotion). Areas of 100 cm2 should be treated with multiple in-motion passes to reach a cumulative energy dose between 6 and 10 kJ [73]. However, some studies showed that this technology is more successful with coarse hair and darker skin type [74].

Lasers

71

Fig. 2.16 Clinical indications interface. The operator can use the suggested treatment parameters by feeding his input in the clinical indications interface window

Fig. 2.17  Concept of gradual heating that induces incipient necrosis and perifollicular edema in dynamic SHR

Another observation is that hair grows back into finer and lighter follicles that are more challenging to remove by laser [62]. Therefore, Alma laser introduced the Soprano ICE platform with an additional alexandrite handpiece to deal with fine hair. Later, Alma Laser introduced the Soprano ICE Platinum, which offers three wavelengths 755, 810, and 1064. According to the attached tip, the applicator emanates one wavelength during the treatment. The newer Soprano Titanium emits the three wavelength simultaneously [36]. Comparison Table 2.13 compares five different diode laser systems in SHR mode in terms of available wavelength, pulse width, maximum energy, treatment modes, and other features.

72

2  Laser and Intense Pulsed Light

Table 2.13  Comparison of five different diode laser systems in SHR mode System name Wavelength LightSheer 808 nm Duet

Pulse width Handpiece 5–400 Vacuum ms handpiece and 9 × 9 mm standard handpieces with continuous contact cooling

LightSheer 805 nm Desire

5–400 Vacuum ms handpiece, 12 × 12 and 9 × 9 mm standard handpieces with continuous contact cooling

LightSheer 805 and Quadro 1060 nm

5–400 Vacuum ms handpiece, 12 × 12 and 9 × 9 mm standard handpieces with continuous contact cooling

Max fluence Up to 12.5 J in the vacuum handpiece and 100 J/ cm2 in the 9 × 9 contact handpiece Up to 12.5 J in the vacuum handpiece and 100 J/ cm2 in the 9 × 9 and 40 J/cm2 in the 12 × 12 contact handpieces Up to 12.5 J in the vacuum handpiece and 100 J/ cm2 in the 9 × 9 and 40 J/cm2 in the 12 × 12 contact handpieces

Treatment mode Static, with or without vacuum

Features Standard and vacuum handpieces

Static, with or without vacuum

Standard and vacuum handpieces

Static, with or without vacuum

The dual-­ wavelength, standard, and vacuum handpieces

Three diode wavelengths, special handpiece for ear and nostril hair removal Three diode wavelengths, special 3D handpiece, handpiece for ear and nostril hair removal

Soprano ICE from Alma

755, 810, 1064 nm

Three different handpieces, one for each wavelength

Dynamic

Soprano ICE platinum and titanium from Alma

755, 810, 1064 nm separate and in trio technology (3D)

It has three different handpieces, one for each wavelength, and a 3D handpiece that emits the three wavelengths simultaneously

Dynamic

Lasers

73

1064 nm ND:YAG Laser This is aesthetic practice’s most versatile laser cornerstone [75]. The lower melanin absorption and low melanin/oxyhemoglobin ratio allow us to use this wavelength: LHR, benign pigmentation removal, vascular lesion, and photorejuvenation in darker skin types (III–VI). By changing pulse width, fluence, spot size, and repetition rate, practitioners can target the correct depth to target a specific lesion. However, this laser’s deep penetration may increase the risk of deep tissue damage, such as fat atrophy. Comparison As we discussed earlier, on the section with “Alex laser,” most available platforms provide 755 and 1064  nm wavelengths. Almost all new platforms, as observed before, contain an Nd:YAG laser and other light sources such as IPL and fractional ablative and non-ablative lasers. Some YAG platforms offer an extralong pulse of 1064 nm, up to 5 s; at this pulse width, the gentle bulk heating occurs at the deep dermis layer to help photorejuvenation, skin tightening, and body shaping like the Piano Mode in Fotona Dynamis, as shown in Fig. 2.18 [76]. GentleMax The reader can refer to the section on GentleMax in “755  nm Alexandrite (Alex) Laser.” Short Q-Switched Nanosecond (ns) Laser The pulse width gets 1,000,000 shorter as we move from the ms to the ns range (5–7 nm). As a result, the ns range pulses have a much higher energy peak, as shown in Fig.  2.18 [77]. The ns laser is suitable to heat small targets with a short thermal relaxation time. The heat buildup is rapid enough to overcome the TRT and reach a clinically significant temperature. The indications of the Q-switch lasers are simple POWER Q-SWITCH

Megawatts

FRAC3 Kilowatts

LP

NEW MODE

Fig. 2.18 Relations between the pulse width and energy of the Nd:YAG laser. All traditional Nd:YAG laser platforms provided only the ms range

PIANO

Watts

TIME Nanoseconds Microseconds Miliseconds

Seconds

74

2  Laser and Intense Pulsed Light

and advanced pigmentation correction, photorejuvenation, and tattoo removal. More importantly, as discussed before, the laser shows significant photoacoustic properties at this short pulse width. Some systems have the quick pulse-to-pulse mode (Q-PTP), enabling greater energy delivery by shooting two pulses 80 μs apart to enhance the laser’s safety and tolerability [78]. 532 nm KTP Just like what we discussed about the long-pulsed 532  nm laser, the use of this wavelength is restricted to skin types I and II. With low fluences and larger spot size, this laser in the ns range provides a medium-depth laser peel with less downtime and high patient satisfaction. However, one thing about it is that it should be used only after a test patch (test spot), with proper sun protection after treatment. Besides, it can be used for superficial vascular lesions and effective treatment for lip lightening [79]. Usually, the 1064 nm is the main wavelength in all Q-switch systems, and the 532 nm is, by default, complimentary. Thus, we will postpone the comparison section and include it under the Q-switch 1064 nm ns laser [80]. 585 and 595 nm Pulsed Dye Lasers (PDL) The Q-switched ns PDL 2 mm spot-size handpiece is an add-on to most Q-switched laser systems for colored tattoo removal [81]. However, using this laser with larger spot size (5 mm) and low fluence is an efficient tool to correct inflammatory and postinflammatory erythema in acne, hypertrophic scars, and stretch marks combined with other lasers [82]. Practitioners should be aware that the 2 mm handpiece doesn’t deliver enough depth for the previously mentioned indications, other than tattoo removal. 1064 nm ND:YAG Laser This is the most studied and used Q-switched laser with a similar indication to the 532 nm but a much better safety profile. Melasma is commonly treated with a low-­ fluence Q-switched Nd:YAG laser, which is considered safe and relatively effective, but not as monotherapy [80, 83, 84]. The melanocytic and pigmentation lesions will be discussed in detail in different chapters. Comparison Table 2.14 compares four different 1064  nm Q-switch laser systems in terms of available wavelength, cooling mechanism, operation interface, maximum energy, and pulse width. https://drive.google.com/file/d/1z7CukKd5PZYtLOpEYqmYHjZMapYTjuZT/ view?usp=share_link

75

Lasers Table 2.14  Comparison of four different 1064 nm Q-switch laser systems System name Alma Q

Wavelength 532, 585, 640, and 1064 nm

Pulse width Q-switched, long, and quasi-long

532, 585, 640, and 1064 nm

Q-switched and quasi-long

Fotona 532, 585, StarWalker 640, and 1064 nm

Q-switched, long, and quasi-long

Cynosure RevLite

300 ps

Lutronic Spectra a

532, 585, 640, and 1064 nm

Fluence range Max single pulse energy is 0.45 J and 1.2 J for 532 and 1064

Max single pulse energy is 0.45 J and 1.2 J for 532 and 1064 Max single pulse energy is 10 J for 532 and 1064 Max single pulse energy is 0.45 J and 1.2 J for 532 and 1064

Handpieces Zoom (1–7 mm), collimated (8 mm), square (5 × 5 mm), and fractional (7 × 7 mm) Collimated (2–8 mm), gold toning 5 mm handpiece

Features Long-pulsed and Quasi-long-­ pulsed, fractional handpiece (add-on), Q-PTP Q-PTP

Collimated (2–8 mm), fractional

ASPb

Collimated (3–8 mm)

Q-PTP

This video shows the Lutronic Spectra laser device and discusses different treatment parameters Adaptive Structured Pulse (ASP) permits the laser pulses to be shaped in ways that may be more favorable, such as switching from a square pulse form to something more complicated, which might have more indication in the dental application [85] a

b

Lutronic Spectra Interface An illustration of the Lutronic Spectra is shown in Fig. 2.19 [86]. Ultrashort Picosecond (ps) Laser In the last decade, a great deal of research focused on improving the peak and reducing the total energy of the laser pulse by reducing the pulse width from ns to the ps range [87]. The first generation of picosecond laser (PicoSure) was disappointing in performance and suffered some maintenance issues. The second-generation picosecond laser emerged with more robust performance and multi-wavelength configuration [24]. In ultrashort time, the intense energy delivery mode correlates with a high-power peak in the gigawatt (GW) range and enhanced photoacoustic vibration. Hence, just like Q-switched, ps lasers are indicated for benign pigmentation, acne scarring, stretch marks, photorejuvenation, and tattoo removal. Below is a sample of PicoWay (a second-generation picosecond laser) indication according to wavelengths, skin types, and parameters [24] (Table 2.15).

76

2  Laser and Intense Pulsed Light

Fig. 2.19  Operation interface window for the Spectra laser. The touch screen has the following indicators: (1) Reset button. (2) Pulse rate. (3) Spot size is an indicator that shows the spot size chosen on the handpiece. (4) Aiming beam adjustor. (5) Fluence. (6) Wavelengths: the 1064 and 532 are in the ns range; Spectra 1064 nm in the μs range (quasi-long). (7) Memory. (8) Toning: special function for melasma treatment. It operates on low fluence, large spot size, and low repetition rate. (9) Setup Table 2.15  Cleared indication for the PicoWay laser platform from Candela as reported by a panel of experts [88]

Lasers Table 2.15 (continued)

77

2  Laser and Intense Pulsed Light

78

Comparison Table 2.16 compares five different picosecond laser systems in terms of available wavelength, pulse width, fluence, and other features.

Color-Blind Lasers Resurfacing Lasers In this book, these lasers use skin water molecules as chromophores called color-­ blind lasers. These lasers have longer wavelengths than the color-sensitive ones and are in the more extended range to match the water absorption spectrum [56]. The photothermolysis of resurfacing lasers is not specific to the pigmented lesion but relies on peeling the skin layer that contains the unwanted pigment. Older systems used to be non-fractional; however, all current systems adapted the “fractional” function due to higher safety, shorter downtime, and better results [89]. A fractional Table 2.16  Comparison of five different picosecond laser systems System name Discovery by Quanta

Laser wavelength 532, 694, 1064 nm

Fluence Pulse width range 450 ps for the 600 mJ (1.8 1064 nm GW) for the 1064 nm

PicoWay 532, 785, by Candela 1064 nm

450 ps for the 1064 nm

PicoSure by Cynosure

750 ps for the 755 nm, the actual pulse width for 1064 nm is not revealed 300 ps for the 1064 nm

532, 755, and 1064 nm

Pico Clear 532, 585, by Alma 640, and 1064 nm

PicoPlus by Lutronic

532, 585, 660, and 1064 nm

200 mJ (0.36 GW) for the 755 nm

Handpieces Round Zoom (2–10 mm), fractional (7 × 7 mm), and square (5 × 5 mm) Round zoom (2–10 mm), fractional (6 × 6 mm) Round collimated (2–6 mm), round fixed (6,8, and 10 mm)

450 mJ (1.3 Round (2–10 GW) for the mm), fractional 1064 nm (7 × 7 mm), and square (5 × 5 mm) 450 ps for the 800 mJ (2.2 Round zoom 1064 nm GW) for the (2–10 mm), 1064 nm round collimated (2–6 mm)

Features A second generation with complete Nd:YAG pulse mode profiles (long, short, and ultrashort) The second generation, fractional handpiece A first-generation pico laser with a focus lens to distribute energy into microbeams A second generation, PTP, four wavelengths

A second generation, focus lens, distributes energy into microbeams

Lasers

79

laser handpiece divides the laser beam into microscopic columns called microthermal zones (MTZ). So, the laser beam does not hit skin as one thick beam but in a non-continuous fractionated pattern. The result is a pattern of alternative treated and non-treated microscopic dots on the skin [46]. The untreated areas facilitate healing, resulting in higher safety and shorter downtime than the non-fractional ones [90]. It is important to clarify that the inverse relationship between the spot size and the penetration is not valid at the fractional microscopic level. The laser’s MTZ is delivered by either a stamping handpiece, a roller tip, or a scanner handpiece (a scanner is usually an add-on for an extra charge). A scanner is a very beneficial add-on to fractional lasers as it allows practitioners to change the shape and the percentage of treated/untreated spots. Some platforms (such as Fraxel Dual) would allow the practitioner to choose the relative percentage between the treated and non-treated areas without needing a scanner. The interaction between these lasers and skin water is either coagulation, ablation, or both, depending on the wavelengths and the fluence. The following pictures show skin irradiation histology by one of the most commonly used resurfacing lasers, 1550, 1927, 2940, and 10,600 nm [91]. Fractional Non-ablative Lasers (FNAL) These lasers have shorter wavelengths than ablative lasers and thus have less affinity for water. Diode 1410 nm, Nd:YAG 1440 nm, Er:Glass laser 1550 nm, and Thulium 1927 nm are the most well-known FNAL. Because Er:Glass has a lower affinity for water, it can penetrate deeper and produce a stronger coagulation effect. The penetration depth increases in direct proportion to the energy output. When the energy of a 1550 nm laser increases from 6 mJ to 70 mJ, the penetration depth increases from 0.4 mm to 1.4 mm. The result of FNAL interaction with the skin is mainly coagulation. Coagulation is a process through which a liquid material turns solid or semisolid. The heated water molecule causes collagen’s denaturation (coagulation zones), which mimics the wound environment. The coagulation zones’ existence induces the skin to go through the wound healing process and produce more collagen, as shown in Fig. 2.20 [92, 93]. FNAL wavelengths do not damage the stratum corneum and leave it intact because of low water content. Therefore, FNAL lasers do not cause pinpoint bleeding but result in noticeable redness and erythema. The Er:Glass lasers are the most studied laser among all FNAL, with benign hyperpigmentation, scar correction, stretch marks, and general skin rejuvenation [94]. Moreover, their effectivity and high safety profile make them a popular addition to most platforms. For example, Lumenis M22 contains universal IPL, long-pulsed/Q-switched Nd:YAG and 1556 FNAL. Fraxel Dual from Solta includes two wavelengths, 1550 and 1927 nm, to improve the coagulation/resurfacing ratio. The depth of penetrations depends mainly on laser energy, as shown in Fig. 2.21.

80

2  Laser and Intense Pulsed Light

Microscopic Epidermal Necrotic Debris (MEND)

Controlled Zones of Denatured Collagen in the Dermis

100um

Fig. 2.20  Zones of denatured collagen in the dermis after fractionated laser beam and the microscopic epidermal necrotic debris being expelled on day 16. Healing occurs from surrounding viable tissue, and there is complete re-epithelization in 24 h

Fig. 2.21  Human skin and penetration depth of 1550 nm Er:Glass (Fraxel laser) with corresponding energy settings [93]

Lasers

81

As mentioned previously, two laser delivery patterns are continuous roller movement (Fraxel dual) and a stamp with a scanner (Alma Hybrid). Laser devices with rollers are associated with significant consumable costs (Table 2.17). The level of treatment and the coverage percentage with Fraxel laser correlate to redness and swelling of Fraxel treatment, as shown in Fig. 2.22 [93]. Table 2.17  Recommended treatment settings for approved indications of the 1550 nm erbium-­ doped and 1927 nm thulium laser system and treatment settings for combination treatment [95]

Treatment Levels and Percent Coverag 1

2

3

5%

7%

9%

Lowest

4

5

6

7

8

9

10

11

12

R1

R2

R3

11% 14% 17% 20% 23% 26% 29% 32% 35% 38% 43% 46% Edema Erythema

Highest

Fig. 2.22  Percentage of skin treated per session and the amount of redness a patient would experience. If the patient is prone to prolonged redness and swelling, the settings can be adjusted to achieve a better result. For near-total coverage in five treatments, we recommend treating at level 9 [93]. This video shows optimizing FNAL parameters using the Fraxel Dual laser device: https:// drive.google.com/file/d/1G0bW-­80xHvipwN-­o4BfxY4gmmMkmG-­gh/view?usp=share_link

82

2  Laser and Intense Pulsed Light

Comparison Table 2.18 compares five different non-ablative laser systems in terms of available wavelength, maximum depth, beam diameter, treatment mode, available handpiece, and other features. Table 2.18  Comparison of five different non-ablative lasers Max System coagulation Beam Delivery name Wavelength depth diameter pattern Fraxel 1550/1927 nm 1.5 mm 63 μm Roller Dual from Solta

Microlens 1540 nm 1550 nm from Cynosure

1 mm

ResurFX from Lumenis

1540

0.15 mm

Halo laser 1470 from Sciton

Not revealed

Alma Hybrid

1 mm

1570/10600

ClearSkin 1540 nm in Er:Glass Harmony Alma Pixel® 1320 nm 1320 nm Nd:YAG from Alma

NA

2–4 mm

handpieces One handpiece with two different tip sizes

Features A stand-alone system, two FNAL wavelengths Has substantial consumable use 230 μm Stamping Deep (XD) Part of the Icon (stamp) and Fast platform (XF) alongside IPL, handpieces long-pulsed Nd:YAG, and fractional 2930 nm ablative laser 400 μm Stamping Coolscan A stand-alone or (scanner) scanner part of the M22 platform, a scanner with contact cooling 0.25, Roller One Halo Pro was the 3.7, and handpiece first Hybrid 5 ms with two 1470/2940 fractional fractional zones of non-ablative/ 10 × 10 and ablative 6 × 6 mm handpiece 400 μm Static Scanner Contact cooling, (scanner) with contact Hybrid cooling 1570/10600 fractional non-ablative/ ablative handpiece with radiofrequency 600–100 Static 2 mm Integrated mJ/P cooling vacuum The vacuum can be turned on/off Not Static 7 × 7 mm Variable pulse revealed handpiece widths 30–40–50 with two ms for darker Pixel counts skin types (49 and 81)

Lasers

83

Halo Laser One example of the non-ablative/ablative combination is Halo. The hybrid Halo is a fractional laser that irritates the skin with a combo of 1470 and 2940 nm simultaneously, as shown in Fig. 2.23. Coverage (or density) becomes important when dealing with fractional lasers. A larger coverage indicates that a higher portion of the skin is irritated with laser. The coverage percentage ranges between 5 and 25% on most platforms, and a higher density correlates with more aggressive treatment and longer downtime. Figure 2.23 shows the treatment area divided into five face zones when using Halo. By pressing this soft key, users are sent to the data entry page, where they may enter the length and breadth of these zones in cm2. The dimensions can be input by simply running the Halo handpiece down the length (and breadth) while holding down the footswitch or by physically measuring the dimensions and entering them using the “+” or “−” soft keys.

Fig. 2.23 Operation interface window for the Halo laser from Sciton

84

2  Laser and Intense Pulsed Light

1. Keys to selecting the treated area. 2. Reset softkey. 3. This bar provides a graphical representation of the fraction of the selected percent coverage. 4. Target % of coverage selected for the treatment. 5. This number represents the current percentage of treatment area coverage. 6. The velocity meter displays visual feedback on the proper velocity of handpiece movement. 7. The target energy to be delivered is displayed here, calculated based on the target % coverage selected. 8. The energy display is where the total energy delivered is displayed. 9. The Skin Temp indicator displays the skin temperature automatically during treatment. 10. Touching the Treatment Summary soft key takes the user to the Treatment Summary screen, which displays the treatment area, target/delivered energy, and 1470 depth/coverage for the five treatment zones. 11. Adapter Life Time Indicator: The indicator shows how long the disposable adapter has been used. The disposable adapter has a 90-minute life span. The indicator will track the amount of time spent. 12. Preset Depth (m)/Coverage (percent) soft key for HALO 1, HALO 2, and HALO 3: Touching one of these three soft keys allows the user to choose between the predefined depth (m), coverage, and density (percent).

HALO1 Depth ( µ m ) / Coverage ( % ) is 300 / 5



HALO 2  Depth ( µ m ) / Coverage ( % ) is 300 / 10





HALO 3  Depth ( µ m ) / Coverage ( % ) is 350 / 10





13. The depth and coverage indicator displays the depth and % coverage selected for treatment with HALO 1, HALO 2, or HALO 3. 14. Scan Width displays the HALO disposable adapter width in mm. 15. When raising the density, consider the patient’s skin type and history of pigmentary disorders, such as hyper- or hypopigmentation. 16. Standby soft key: The system is in idle or standby mode. Pressing this soft key will bring the user to Ready mode, and the system will be active. 17. The user will be returned to the 1470 nm/2940 nm apps by pressing this soft key. Fractional Ablative Lasers (FAL) Light absorption in water increases about 100 times as the wavelength increases from 1550 nm with Er:Glass laser to 2940 nm with Er:YAG laser. This is why ablative lasers evaporate water as well as certain epidermal layers. The only FALs on the market are the 2790 nm Cr:YSGG, the 2940 Er:YAG, and the 10,600 CO2 lasers.

Lasers

85

The 2940 nm laser has the greatest affinity for water, ten times that of CO2 and three times that of Cr:YSGG. Cold (Er:YAG), warm (Cr:YSGG), and hot lasers are the most common (CO2). Figure  2.24 depicts how all three lasers may produce the same ablation but with varying degrees of thermal diffusion [96]. These lasers are used in hyper-/hypopigmentation, rejuvenation, and acne. However, they are usually reserved for deep wrinkles and scars [94, 97]. FAL usually offers a combination of ablation and coagulation based on its water affinity. This is called the ablation/coagulation ratio. Over the last two decades, several technological advancements improved the ability to control and customize the ablation/ coagulation ratio for different indications. Most platforms are equipped with a basic stationary stamp handpiece to be upgraded to a full scanner if required. What Is Stacking Stacking is essential in all laser treatments, especially ablative lasers. Similar to the train of pulses (sequential pulses) in the IPL, ablative laser platforms repeat the laser shot at the same MTZ several times. Practitioners might use stacking to achieve deeper ablation or coagulation without the undesired thermal diffusion associated with greater pulse width. This technique significantly improved the safety and tolerability of FAL and reduced erythema and downtime. Practitioners should consult the manufacturer to understand how they used the term “stacking” in their publications. In some manuals, stacking means that the same pulse is divided into micro-pulses, but the same total energy would be delivered during the same pulse width, as shown in Fig. 2.25 [98]. Higher stacking is usually related to lower erythema and downtime. It is important to refer to the user manual for each laser machine, as stacking might be interpreted differently. Repetition rate refers to the interval between every pulse and is related to overlapping the practitioner technique in moving the handpiece. In others, stacking is used interchangeably with repetition and the number of passes [99]. ABLATION DEPTH 0-5 µ m

6-20 µ m

21-100 µ m

THERMAL DEPTH

8-15µ m 16-30µ m

“Er:YAG’’

“CO2’’

3-7 µ m

Er:YAG

Fig. 2.24  Difference between the Er:YAG and CO2 lasers in terms of ablation/coagulation ratio [96]

86

2  Laser and Intense Pulsed Light

Smart stack 1

Smart stack 2

Smart stack 3

Smart stack 5

Time

Time E= 1×30 mJ

Power

Power

Decreasing Erythmea

Dwell Time: Dwell Time: Dwell Time: Dwell Time: 1000µs 500µs 300µs 200µs DOT Energy: DOT Energy: DOT Energy: DOT Energy: 30mJ 30mJ 27mJ 30mJ

E= 5×6 mJ = 30mJ

Fig. 2.25  Difference between five stacking modes in the SmartXide DOT CO2 laser from Deka [98]

2940 ER:YAG and CR:YSGG 2790 nm Laser These two wavelengths have the highest affinity to water and, thus, the highest ablation properties. The Er:YAG is the most ablative laser, referred to as a cold laser due to minimal thermal diffusion, followed by the 2790 nm laser (the warm laser). The first generation of Er:YAG systems had a stationary pulse width between 0.25 and 0.3 ms, with a single indication of resurfacing without significant coagulation and remodelling. This feature has had fewer side effects, such as PIH. Nevertheless, the 2940 and 2790 nm laser’s versatility was limited in the aesthetic field by its high ablation/coagulation ratio. The second generation of the Er:YAG laser systems overcame this problem by presenting a variable pulse width. With this, practitioners can achieve an adequate ablation/coagulation ratio by controlling the pulse width. The high-peak short pulse is usually purely ablative. The coagulation increases as we increase the pulse width allowing more thermal diffusion. Besides, the shape of the pulse width has improved, to exclude the long tail and reduce energy waste, as shown in Fig. 2.26 [49]. The Fotona Dynamis and Joule are the only fully functional Er:YAG systems with variable pulse width and scanner attachment. This video shows the Fotona Dynamis laser and discusses different parameters for the fractional ablative treatment: https://drive.google.com/file/d/1IW-­ FQO8mNYyHlTTUlf2v7S0OE_BZgFhf/view?usp=share_link This video shows the relations between the pulse width and the application of Er:Yag laser applications: https://drive.google.com/file/d/1JzNlu2NUwbUB8NOfk 15Qs7JIRxR5afEm/view?usp=share_link. Comparison Table 2.19 compares four Er:YAG laser systems in terms of available wavelength, maximum ablation depth, pulse width, stacking, handpieces, and other features.

Lasers

87

LASER PULSE POWER

STANDARD LASER TECHNOLOGY

FOTONA VSP TECHNOLOGY VSP SP LP VLP

Slow rise time

Long tail 0

0

400 TIME

800

1200

1600

0

400

800

1200

1600

(micro seconds)

Fig. 2.26  Difference between standard Er:YAG pulse technology and the variable square pulse (VSP) technology in the Fotona laser platform, courtesy of Fotona Table 2.19  Comparison of four Er:YAG laser systems System name Fotona Dynamis

Ablation Pulse Wavelength depth width 2940 nm 400 μm 175–800 μs

Joule from 2940 nm Sciton

400 μm

Variable, actual data not revealed

Stacking handpieces Yes Fully ablative, fractional, scanner, vaginal

Yes

Features Full control over ablation/ coagulation ratio to expand treatment options. Actual variable square pulse (VSP) The Dynamis platform is integrated with a variable pulse 1064 nm ND:YAG laser Fully ablative, The platform comes with several fractional, additional options, scanner, including a hybrid vaginal, 1470/2940 NM hybrid Halo handpiece, 1064 nm, and IPL (extra charge) (continued)

2  Laser and Intense Pulsed Light

88 Table 2.19 (continued) System Ablation name Wavelength depth 2940 nm 90 μm iPixel 2940 from Harmony Alma

2940 fractional from Icon

2940 nm

xeo Pearl fractional from Cutera

2790 nm

Pulse width Fixed 2 ms for 7 × 7 Variable for the roller 10 mm thermal tip No 0.25, 3.7, revealed and 5 ms

100 μm

600 μs

Stacking handpieces Features Add-on to the No Handpiece Harmony platform with a 7 × 7 fractional zone Handpiece with 7 × 1 roller

No

No

One handpiece with two fractional zones of 10 × 10 and 6 × 6 mm Fully ablative handpiece and a fractional handpiece

Add-on to the Icon platform

It can be used in skin types I–III only

Fotona Dynamis The operator interface for Fotona Er:YAG is interactive and intuitive. The operator can choose the level of ablation and coagulation, and the computing system will suggest a suitable setting, including fluence and pulse width, as shown in Fig. 2.27. iPixel ER:YAG 2940 nm 2 Hz Applicator; 7 × 1 iPixel Roller Table 2.20 shows the treatment parameters using iPixel Er:YAG from Alma. 10,600 nm CO2 Laser The CO2 laser systems have evolved in aesthetics and dermatology since the 1990s. The first generation of CO2 laser systems has a continuous wave (CW) mode. This delivers low but continuous energy. In contrast, the CW mode has unfavorable thermal diffusion to the surrounding tissue and its ablation/coagulation ratio. Therefore, their use in the aesthetic field was limited due to adverse effects, mainly PIH. The second generation of CO2 laser introduced the super pulse principle, in which the energy is delivered in a discrete, intense pulse. The super pulse mode, with its sharp peak and short tails, has significantly improved the ablation/coagulation ratio and reduced thermal diffusion to the surrounding tissue. The latest generation uses the ultra pulse concept, where the energy pulse has a more consistent rectangle shape without tails. We use the term Char-Free due to its

Lasers

89

Fig. 2.27  Operator interface window for the variable square pulse (VSP) in the Fotona laser platform. By choosing the level of ablation and coagulation on the left, the system will suggest the setting for a given handpiece to reach the treatment goals Table 2.20  Treatment parameters using iPixel Er:YAG from Alma Fitzpatrick skin type I–III IV I–III IV I–III IV

Treatment intensity Mild Mild Moderate Moderate Aggressive Aggressive

Pulse mode Short Short Medium Medium Long Long

Energy (mJ/P)