Diagnostic radiology : chest and cardiovascular imaging [3 ed.] 9788184488685, 8184488688

Table of contents :
Prelims
Chapter-01_Chest X-ray Technique and Anatomy
Chapter-02_Mdct Chest Technique and Anatomy
Chapter-03_Basic Patterns of Lung Diseases
Chapter-04_Radiographic Manifestations of Pulmonary Tuberculosis
Chapter-05_Nontubercular Pulmonary Infections
Chapter-06_Imaging of the Tracheobronchial Tree
Chapter-07_Imaging of Interstitial Lung Disease
Chapter-08_Pulmonary Manifestations in Immunocompromised Host (HIV and Solid Org
Chapter-09_Chest in Immunocompromised Host (Hematological Infections and Bone Ma
Chapter-10_Imaging the Mediastinum
Chapter-11_Imaging of Solitary and Multiple Pulmonary Nodules
Chapter-12_Lung Malignancies
Chapter-13_Intensive Care Chest Radiology
Chapter-14_Imaging in Pulmonary Thromboembolism
Chapter-15_Imaging in Thoracic Trauma
Chapter-16_Pleura
Chapter-17_Imaging of the Diaphragm and Chest Wall
Chapter-18_Bronchial Artery Embolization
Chapter-19_Diagnostic and Therapeutic Interventions in Chest
Chapter-20_Chest X-ray Evaluation in Cardiac Disease
Chapter-21_Imaging in Ischemic Heart Disease
Chapter-22_Imaging Approach in Children with Congenital Heart Disease
Chapter-23_Imaging in Cardiomyopathies
Chapter-24_Imaging Evaluation of Cardiac Masses
Chapter-25_Imaging Diagnosis of Valvular Heart Disease
Chapter-26_Imaging of the Pericardium
Chapter-27_Nuclear Medicine in Cvs and Chest
Chapter-28_Imaging of Aorta
Chapter-29_Imaging of Peripheral Vascular Disease
Index

Citation preview

DIAGNOSTIC RADIOLOGY CHEST AND CARDIOVASCULAR IMAGING

AIIMS–MAMC–PGI IMAGING COURSE SERIES

Manorama Berry

Sudha Suri

Veena Chowdhury

PAST EDITORS

Sima Mukhopadhyay

Sushma Vashisht

DIAGNOSTIC RADIOLOGY CHEST AND CARDIOVASCULAR IMAGING THIRD EDITION EDITORS Veena Chowdhury  MD

Director-Professor and Head Department of Radiodiagnosis Maulana Azad Medical College New Delhi, India

Arun Kumar Gupta  MD MNAMS

Professor and Head Department of Radiodiagnosis All India Institute of Medical Sciences New Delhi, India

Niranjan Khandelwal  MD Dip. NBE FICR

Professor and Head Department of Radiodiagnosis Postgraduate Institute of Medical Education and Research Chandigarh, India

ASSOCIATE EDITORS

Sanjiv Sharma MD

Anjali Prakash  DMRD DNB MNAMS

Professor and Head Department of Cardiac Radiology CN Center All India Institute of Medical Sciences New Delhi, India

Professor Department of Radiodiagnosis Maulana Azad Medical College New Delhi, India

®

JAYPEE BROTHERS MEDICAL PUBLISHERS (P) LTD. New Delhi • St Louis (USA) • Panama City (Panama) • Ahmedabad • Bengaluru • Chennai Hyderabad • Kochi • Kolkata • Lucknow • Mumbai • Nagpur

Published by Jitendar P Vij Jaypee Brothers Medical Publishers (P) Ltd Corporate Office 4838/24 Ansari Road, Daryaganj, New Delhi - 110002, India, Phone: +91-11-43574357, Fax: +91-11-43574314 Registered Office B-3 EMCA House, 23/23B Ansari Road, Daryaganj, New Delhi - 110 002, India Phones: +91-11-23272143, +91-11-23272703, +91-11-23282021 +91-11-23245672, Rel: +91-11-32558559, Fax: +91-11-23276490, +91-11-23245683 e-mail: [email protected], Website: www.jaypeebrothers.com Offices in India • Ahmedabad, Phone: Rel: +91-79-32988717, e-mail: [email protected] • Bengaluru, Phone: Rel: +91-80-32714073, e-mail: [email protected] • Chennai, Phone: Rel: +91-44-32972089, e-mail: [email protected] • Hyderabad, Phone: Rel:+91-40-32940929, e-mail: [email protected] • Kochi, Phone: +91-484-2395740, e-mail: [email protected] • Kolkata, Phone: +91-33-22276415, e-mail: [email protected] • Lucknow, Phone: +91-522-3040554, e-mail: [email protected] • Mumbai, Phone: Rel: +91-22-32926896, e-mail: [email protected] • Nagpur, Phone: Rel: +91-712-3245220, e-mail: [email protected] Overseas Offices • North America Office, USA, Ph: 001-636-6279734, e-mail: [email protected] [email protected] • Central America Office, Panama City, Panama, Ph: 001-507-317-0160, e-mail: [email protected] Website: www.jphmedical.com Diagnostic Radiology: Chest and Cardiovascular Imaging © 2010, Jaypee Brothers Medical Publishers All rights reserved. No part of this publication should be reproduced, stored in a retrieval system, or transmitted in any form or by any means: electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the editors and the publisher. This book has been published in good faith that the material provided by editors is original. Every effort is made to ensure accuracy of material, but the publisher, printer and editors will not be held responsible for any inadvertent error (s). In case of any dispute, all legal matters are to be settled under Delhi jurisdiction only. First Edition: 1996 Second Edition: 2003 Third Edition: 2010 ISBN 978-81-8448-868-5 Typeset at JPBMP typesetting unit Printed at Ajanta Offset

Contributors Akshay Kumar Saxena  MD

Deep Narayan Srivastava  MD MNAMS

Anupam Lal  MD

Gurpreet Singh Gulati  MD

Associate Professor Department of Radiodiagnosis Postgraduate Institute of Medical Education and Research, Chandigarh, India

Associate Professor Department of Radiodiagnosis Postgraduate Institute of Medical Education and Research, Chandigarh, India

Anjali Prakash  DMRD DNB MNAMS

Professor Department of Radiodiagnosis All India Institute of Medical Sciences New Delhi, India

Associate Professor Cardiovascular and Interventional Radiology Cardiothoracic Center All India Institute of Medical Sciences New Delhi, India

Professor Department of Radiodiagnosis Maulana Azad Medical College New Delhi, India

Jyoti Kumar  MD DNB MNAMS

Anju Garg  MD

Kushaljit Singh Sodhi  MD

Arun Kumar Gupta  MD MNAMS

Madhavi Chawla  MBBS DNB (Nuclear Medicine)

Ashu Seith Bhalla  MD

Mahesh Prakash  MD

Atin Kumar  MD MNAMS DNB

Mandeep K Garg  MD FRCR

Professor Department of Radiodiagnosis Maulana Azad Medical College New Delhi, India

Professor and Head Department of Radiodiagnosis All India Institute of Medical Sciences New Delhi, India

Associate Professor Department of Radiodiagnosis All India Institute of Medical Sciences New Delhi, India

Assistant Professor Department of Radiodiagnosis Trauma Centre All India Institute of Medical Sciences New Delhi, India

Chetan Patel  MBBS DRM DNB (Nuclear Medicine) Associate Professor Department of Nuclear Medicine All India Institute of Medical Sciences New Delhi, India

Assistant Professor Maulana Azad Medical College New Delhi, India

Assistant Professor Department of Radiodiagnosis Postgraduate Institute of Medical Education and Research, Chandigarh, India

Senior Research Associate Department of Nuclear Medicine All India Institute of Medical Sciences New Delhi, India

Assistant Professor Department of Radiodiagnosis Postgraduate Institute of Medical Education and Research, Chandigarh, India

Assistant Professor Department of Radiodiagnosis Postgraduate Institute of Medical Education and Research, Chandigarh, India

Mandeep Kang  MD

Associate Professor Department of Radiodiagnosis Postgraduate Institute of Medical Education and Research, Chandigarh India

vi  Diagnostic Radiology: Chest and Cardiovascular Imaging

Manavjit Sandhu  MD

Sanjay Thulkar  MD

Niranjan Khandelwal  MD Dip. NBE FICR

Sapna Singh  MD DNB MNAMS

Naveen Kalra  MD

Sanjiv Sharma  MD

Priya Jagia  MD

Shivanand Gamanagatti  MD

Professor Department of Radiodiagnosis Postgraduate Institute of Medical Education and Research, Chandigarh, India

Professor and Head Department of Radiodiagnosis Postgraduate Institute of Medical Education and Research, Chandigarh, India

Associate Professor Department of Radiodiagnosis Postgraduate Institute of Medical Education and Research, Chandigarh, India

Assistant Professor Department of Cardiac Radiology All India Institute of Medical Sciences New Delhi, India

Raju Sharma  MD MNAMS

Additional Professor Department of Radiodiagnosis All India Institute of Medical Sciences New Delhi, India

Rashmi Dixit  MD

Professor Department of Radiodiagnosis Maulana Azad Medical College New Delhi, India

Sameer Vyas  MD

Senior Research Associate Department of Radiodiagnosis Postgraduate Institute of Medical Education and Research, Chandigarh, India

Sanjay Sharma  MD FRCR DNB

Associate Professor Department of Radiodiagnosis All India Institute of Medical Sciences New Delhi, India

Associate Professor Department of Radiodiagnosis (IRCH) All India Institute of Medical Sciences New Delhi, India

Assistant Professor Department of Radiodiagnosis Maulana Azad Medical College New Delhi, India

Professor and Head Department of Cardiac Radiology All India Institute of Medical Sciences New Delhi, India

Assistant Professor Department of Radiodiagnosis Trauma Centre All India Institute of Medical Sciences New Delhi, India

Smriti Hari  MD

Assistant Professor Department of Radiodiagnosis All India Institute of Medical Sciences New Delhi, India

Sumedha Pawa  MD

Professor Department of Radiodiagnosis Maulana Azad Medical College New Delhi, India

Veena Chowdhury  MD

Director Professor and Head Department of Radiodiagnosis Maulana Azad Medical College New Delhi, India

Vivek Gupta  MD

Assistant Professor Department of Radiodiagnosis Postgraduate Institute of Medical Education and Research, Chandigarh, India

Preface

to the

Third Edition

The first edition of Diagnostic Radiology on ‘Chest and Cardiovascular Imaging’ was published in 1996. Rapid advances in the field of imaging necessitated revision and the second edition was published in 2003. Chest Imaging continues to be one of the most important and well-established subspecialities of Radiology. Imaging of the lungs and mediastinum requires an understanding of both plain radiography as well as Computed Topography (CT) and other imaging modalities. The phenomenal technical advances in the last few years have changed the practice of chest as well as cardiovascular imaging while retaining the importance of conventional imaging. Cardiovascular imaging has transitioned nearly completely in the past two decades from dependence on X-ray angiography for definite diagnosis to noninvasive cross-sectional imaging techniques. The roles of MRI and MDCT are under rapid evolution. Continuing education is therefore essential so that multimodality imaging approach provides best patient care in a cost-effective manner. We hope that this third edition will serve as a comprehensive updated reference book for postgraduates, practising radiologists, and chest physicians. We wish to take this opportunity to thank our faculty from Maulana Azad Medial College, All India Institute of Medical Sciences and Postgraduate Institute of Medical Education and Research for their active contribution and support without which this endeavor would not have been possible. We would also like to thank Shri Jitendar P Vij (Chairman and Managing Director), Mr Tarun Duneja (DirectorPublishing) and Ms Samina Khan of M/s Jaypee Brothers Medical Publishers (P) Ltd, for their professional help and cooperation in publishing this book in present form. Veena Chowdhury Arun Kumar Gupta Niranjan Khandelwal Sanjiv Sharma Anjali Prakash

Preface

to the

First Edition

It is with great pleasure the faculty of Department of Radiodiagnosis at All India Institute of Medical Sciences, Maulana Azad Medical College, New Delhi, and Postgraduate Institute of Medical Education and Research, Chandigarh present the second book in the series on Diagnostic Radiology. This book is devoted to Emergency and Chest Radiology and has been written to provide the radiologist in training, in practice or teaching, physician and surgeon, an integrated review of the role of various imaging modalities and roentgen features seen in diseases of the chest and in acute emergency situations, both medical and surgical, including trauma. The plain chest radiograph remains the initial imaging modality for various chest diseases and its interpretation continues to be a great challenge. Importance of chest radiograph in the diagnosis of various diseases has been dealt with in depth in all the chapters. Technique of CT and its recent advances in the evaluation of chest diseases and potential of MRI for evaluation of thoracic lesions are covered in separate chapters. Detailed discussion on the clinicopathological aspects and radiology in common thoracic diseases like tuberculosis, nontubercular infections and malignancy, role of HRCT in specific conditions and infections in immunocompromised hosts are included. All the chapters provide information about the recent developments in various fields. Importance of having diagnostic technical facilities and role of a radiologist in handling the patient in acute emergency are highlighted. The increasing use of US and CT as an initial examination in the assessment of acute abdominal conditions has tended to diminish awareness of the value of plain radiography. The role of plain radiograph, US and CT in nontraumatic acute abdomen are covered in separate chapters. Trauma is one of the leading cause of morbidity and mortality. The incidence and severity have sharply increased during the past few decades, primarily because of the increased use of high speed travel. A disciplined approach to the assessment of trauma provides confident interpretation and avoids errors of misdiagnosis. Computed tomography has revolutionized evaluation of a patient with head injury and it remains the first modality of choice. The diagnostic evaluation of patient with craniofacial injury remains problematic because of anatomic complexity of this region, wide spectrum of fracture types, and diversity of soft tissue complication. The proper approach to radiographic diagnosis of appendicular trauma begins by obtaining the appropriate radiographs of each site. Awareness of the common, the often missed and the probable associated injuries improve interpretation and make assessment of radiographs much easier. The role of the radiologist in the management of abdominal trauma has expanded considerably in the recent years. Earlier urography, scintigraphy and angiography played an important role in trauma care. The modalities of CT and interventional radiology have improved the assessment of an injured patient and facilitated nonoperative therapy for some injuries. The proliferation of imaging modalities has increased the possibility of performing inappropriate and unnecessary investigations. The comprehensive discussion on the indications and importance of various imaging techniques in the practice of emergency and chest radiology, a systematic approach for imaging a patient with trauma affecting different organ system are covered in this book. We hope that the reader may find this book both instructive and informative for the improved use of radiological resources which in turn will serve the common goal of good health care for the benefit of patients everywhere. We wish to take this opportunity to thank our faculty colleagues from AIIMS, MAMC, and PGI for their active support, cooperation and timely submission of the manuscripts. We owe immense gratitude to Prof K Subbarao and Prof Ratni B Gujral who have been kind enough to submit their contributions well in time. Manorama Berry Sima Mukhopadhyay Sudha Suri

Contents CHEST IMAGING

Techniques, Normal Anatomy And Basic Patterns In Chest Diseases 1.

Chest X-ray: Technique and Anatomy......................................................................................... 1



Mahesh Prakash, Manavjit Sandhu

2.

MDCT Chest: Technique and Anatomy...................................................................................... 13

3.

Basic Patterns of Lung Diseases............................................................................................... 28



Sumedha Pawa

Deep Narayan Srivastava, Atin Kumar, Shivanand Gamanagatti

Pulmonary Infections And The Pulmonary Interstitium 4.

Radiographic Manifestations of Pulmonary Tuberculosis...................................................... 60



Mandeep Kumar Garg, Naveen Kalra

5.

Nontubercular Pulmonary Infections........................................................................................ 69



Anju Garg

6.

Imaging of the Tracheobronchial Tree....................................................................................... 90



Ashu Seith Bhalla, Raju Sharma

7.

Imaging of Interstitial Lung Disease........................................................................................ 117



Smriti Hari, Sanjay Sharma, Deep Narayan Srivastava

8.

Pulmonary Manifestations in Immunocompromised Host.................................................... 134 (HIV and Solid Organ Transplant Patients)



Mandeep Kang

9.

Chest in Immunocompromised Host (Hematological Infections and Bone Marrow Transplant)..................................................... 145



Sanjay Sharma, Sanjay Thulkar

Mediastinum, Lung Nodules And Masses 10. Imaging the Mediastinum......................................................................................................... 154

Raju Sharma, Ashu Seith Bhalla, Arun Kumar Gupta

11. Imaging of Solitary and Multiple Pulmonary Nodules........................................................... 178

Veena Chowdhury, Sapna Singh

12. Lung Malignancies.................................................................................................................... 212

Sanjay Thulkar, Smriti Hari, Arun Kumar Gupta

Emergency Chest 13. Intensive Care Chest Radiology............................................................................................... 236

Akshay Kumar Saxena, Kushaljit Singh Sodhi

14. Imaging in Pulmonary Thromboembolism.............................................................................. 246

Kushaljit Singh Sodhi, Akshay Kumar Saxena

xii  Diagnostic Radiology: Chest and Cardiovascular Imaging

15. Imaging in Thoracic Trauma..................................................................................................... 259

Atin Kumar, Shivanand Gamanagatti

Pleura And Diaphragm 16. Pleura.......................................................................................................................................... 272

Anjali Prakash

17. Imaging of the Diaphragm and Chest Wall.............................................................................. 301

Sameer Vyas, Anupam Lal

Interventions In Chest 18. Bronchial Artery Embolization................................................................................................. 315

Shivanand Gamanagatti, Ashu Seith Bhalla

19. Diagnostic and Therapeutic Interventions in Chest............................................................... 328

Naveen Kalra, Mandeep Kang, Anupam Lal CARDIOVASCULAR IMAGING

Cardiac Imaging 20. Chest X-ray Evaluation in Cardiac Disease............................................................................ 341

Sanjiv Sharma, Gurpreet Singh Gulati, Priya Jagia

21. Imaging in Ischemic Heart Disease......................................................................................... 349

Gurpreet Singh Gulati, Sanjiv Sharma, Priya Jagia

22. Imaging Approach in Children with Congenital Heart Disease............................................. 366

Priya Jagia, Sanjiv Sharma, Gurpreet Singh Gulati

23. Imaging in Cardiomyopathies.................................................................................................. 376

Priya Jagia, Gurpreet Singh Gulati, Sanjiv Sharma

24. Imaging Evaluation of Cardiac Masses................................................................................... 384

Gurpreet Singh Gulati, Priya Jagia, Sanjiv Sharma

25. Imaging Diagnosis of Valvular Heart Disease......................................................................... 399

Priya Jagia, Sanjiv Sharma, Gurpreet Singh Gulati

26. Imaging of the Pericardium...................................................................................................... 409

Jyoti Kumar

Nuclear Medicine 27. Nuclear Medicine in CVS and Chest........................................................................................ 423

Chetan D Patel, Madhavi Chawla

Vascular Imaging 28. Imaging of Aorta........................................................................................................................ 437

Niranjan Khandelwal, Vivek Gupta

29. Imaging of Peripheral Vascular Disease................................................................................. 459

Rashmi Dixit



Index........................................................................................................................................................... 483

CHEST IMAGING

Techniques, Normal Anatomy and Basic Patterns in Chest Diseases

1

Chest X-ray: Techniques and Anatomy Mahesh Prakash, Manavjit Sandhu

INTRODUCTION Chest X-ray is the most commonly performed radiological investigation around the world and it forms an integral part of the routine study of individual case along with and as important as physical examination and laboratory investigations. The Chest radiograph nearly constitutes 50 to 60 percent of the total work load of the radiology department of any large or small general hospital. The cornerstone of the radiological diagnosis of the chest diseases is chest radiograph. All other radiological procedures including bronchography, computed tomography (CT) and magnetic resonance imaging (MRI) are strictly ancillary.1 The techniques, various radiographic projections and normal anatomy of lungs, mediastinum and diaphragm as demonstrated on plain chest radiographs have been discussed herewith.

CONVENTIONAL CHEST RADIOGRAPHY Conventional film screen radiography using kV range of 50-85 depending on patient’s build is the standard and most commonly used technique for chest evaluation. The benefits of this technique include low cost, high spatial resolution, operation simplicity and dependability. The important factors that influence the contrast in the radiograph include kilovoltage, shape of sensitometric curve of film, exposure parameters and conditions of film processing. At low kV, the difference in attenuation by soft tissue and bone or air and bone is large, resulting in high contrast. Calcified lesions, pleural plaque, pulmonary nodules are well delineated in low kV radiograph. However, some of the limitations of conventional chest radiograph are given here.

• There is poor visibility of mediastinum, retro cardiac and subphrenic areas when lungs are well seen. • Lungs may be obscured by high contrast of bones. • Inadequate detail of airway and lung apices.

Technical Advances Following technical advances have been developed over the years to overcome limitation of the conventional chest radiograph • High kV technique • New film screen combinations • Beam equalization radiography • Digital chest radiography.

High kV Technique In this technique we use more than 120 kV. The coefficient of X-ray absorption of bone and soft tissue approach each other at high kV and thus the lungs are not obscured by bones. It has better penetration of the mediastinum which provides more details of airway. Short exposure time with high kV allows less scatter radiation to reach intensifying screens and results in sharp details of structures within the lungs. However, high kV results in greater scatter radiation as compared to conventional radiography. Use of an air gap of 6 inches is required to reduce scatter radiation.2

New Screen Film Combinations Fine details on radiograph is principally determined by screen film system. Generally, medium speed system is preferred which provided better visualization of small vessels, fissures and depiction of abnormalities. The major advance in screen

2  Techniques, Normal Anatomy and Basic Patterns in Chest Diseases film system has been the introduction of faster rare earth phosphor screen and development of wide latitude film. The improved light emission from rare earth phosphor over traditional calcium tungastate crystal screen results in short exposure time and thus sharp image. Another important development is the introduction of asymmetric screen film system, the asymmetric zero cross over screen film system. It was introduced by Eastman Kodak in 1990 called insight thoracic imaging system.3 This uses different emulsion on either side of film base and different front and back intensifying screens. In addition layers of absorbing dye in the film base prevent crossover of light between two emulsions so that both screen film combinations operate independently. The front side has high resolution screen and high contrast film emulsion. This combination optimizes visualization of fine details in lungs. The back side consists of high speed screen and film emulsion with low maximum density. This combination provides adequate visualization of high attenuating areas eg. mediastinum without over penetration of lungs. Patient dose reduction up to 30 percent has been reported.4 Dupont in 1993 introduced an ultravision screen film system. In this system, screens use a high density rare earth phosphor (yattrium tantalate) which emits ultraviolet light that diffuses substantially less than the lower energy wave length visible light. The film emulsion used is symmetric. These combinations of film screen system have provided increased information that can be recorded and displayed. The asymmetric system is slightly superior particularly for visualization of mediastinal and retro diaphragmatic structures. The improved image sharpness achieved with these systems potentially can improve visualization of subtle parenchymal abnormalities.

BEAM EQUALIZATION RADIOGRAPHY Screen film system provides acceptable image-contrast of chest radiograph in most situations. However, the relatively narrow range of film sensitivity limits image contrast in poorly penetrated areas of chest. The technique of beam equalization radiography refers to varying the intensity of X-ray beam passing through various parts of chest so as to produce a chest radiograph with uniform density of areas with extremely variable attenuation differences on the same film. This can be achieved by two methods:

a. Interposing a customized filter unique to the patient that would attenuate the beam over the lungs and allow increased radiation exposure over the mediastinum. b. Modulation of exposure for each part of the chest by electronic feed back system. The first one lacks practicality, the latter one is the principle used in technique of beam equalization radiography that utilizes screen film receptors by increasing X-ray exposure in the thicker, denser part of chest while keeping the lung exposure unchanged, thereby reducing the dynamic range of intensities that ultimately reach the image recorder.5,6 Oldelft from Netherlands introduced in 1986 the Advanced Multiple Beam Equalization Radiography (AMBER) which is the only commercially available system for chest radiography. This system has horizontal X-ray fan beam which is divided into 20 adjacent beam segments, each of which is independently controlled by its own intensity modulator located in front of X-ray tube and corresponding exposure detector between patient and image recorder. As the fan beam scans the patient, the detector array measure local X-ray intensity passing through the patient and an electronic feed back mechanism dynamically adjust each of beam modulators such that dense areas are imaged at higher exposure levels. This increases signal to noise ratio in the denser areas of chest and shift the background film optical density in these areas on to higher contrast portion of H and D curve. The advantage of this technique are: • Better delineation of mediastinum, retrocardiac and retrodiaphragmatic areas. • Improved visualization of lung apices in lateral view. The reported disadvantage of AMBER are: • Decreased contrast between consolidation and normal lung. • Edge artifacts occur where there are abrupt changes in radiolucency, e.g. lung heart interface ,lung diaphragm interface. • Dark halo around the heart may simulate pneumomediastinum. • Active imaging areas is limited to upright 14” × 17” orientation so it is not possible to acquire transverse image of chest. • Exposure parameter to be set manually • Difficulty in comparing the radiograph of patient with previous one using conventional technique

Chest X-ray: Techniques and Anatomy  3 • This system can not be used on bed side and for patient on stretcher. • Radiation dose is about 50 percent more than conventional chest radiograph. The experience till date is not clearly indicative of the justification of additional expense even though images are more informative and this seems to have limited its popularity in clinical use.

DIGITAL RADIOGRAPHY Advances in electronics and computer technology over the past decades, have led to development of digital radiography or computed radiography system. This is different from conventional film based analogue system where the film is in direct contact with intensifying screen and there is no storage of information as digits in computer. In digital radiography, image detection can be completely separated from image display. The data of image is stored in the computer and can be retrieved, displayed, quantified, manipulated and hard copied whenever required.6 Digital system using phosphor technique in which the entire receptor is exposed by conventional radiography equipment was introduced by Fuji in 1980 and is the most widely used technique for general digital radiography. This technique is based on reusable imaging plate coated with photostimulable phosphor material. When exposed to X-ray, a portion of X-rays is absorbed as to release stored energy as light and intensity of light measured and digitized. The resultant digital image is then preprocessed for contrast and spatial resolution before display. Imaging plate is ready for reuse after exposure to room light. Introduction of selenium detector system is an important development in digital chest radiography. Unlike storage phosphor detector which requires laser stimulation for image acquisition, selenium based detector capture image information as charge pattern and thus image can be read directly, eliminating image noise.7,8 Also selenium is more efficient in detection of X-rays. Flat panel detectors are relatively new development in the technology. Depending on the material, there are two type of flat panel detectors, indirect type use a phosphor screen like cesium iodide to convert the X-ray to light photons. Direct flat panel detectors use instead a photoconductive layer, most commonly amorphous selenium that converts X-ray energy directly to charge. By using flat panel detectors, patient dose

can be reduced without degradation of image quality and multiple images can be acquired in short-time.9,10 Dual energy imaging is a new technique which utilizes a receptor with two layers, each of which records different energy components of X-ray beam and is possible for a computer to analyze and separate the components of dual energy in order to display both soft tissue and bone images of the same radiograph.6 Dual energy imaging is one of the few areas in which digital radiography has proved of diagnostic advantage over conventional chest radiography. Temporal subtraction imaging is used to improve the visual assessment of chest radiograph. This technique aim to selectively enhance areas of internal change by subtracting the patient’s previous radiograph from the current one. Studies have shown that temporal subtraction improves the visual perception of subtle abnormalities such as pulmonary nodules, infiltrative opacities and diffuse lung disease.11,12 Digital tomosynthesis is a technique that has evolved from conventional tomography and solves many of the problems associated with conventional tomography. Digital Tomosynthesis can produce an unlimited number of section images at arbitrary depths from single set of acquisition images. This technique is another method for improving detection of subtle lesions such as pulmonary nodules.13,14

Digital Radiography and Chest Major advantage of digital radiography lies in the control of display of optical density of radiographs in portable chest X-ray examination with dynamic range and control processing. It improves visibility of tubes and lines superimposed on the mediastinum. Although it may not offer any significant advantage over conventional film screen system, Digital radiography improves visibility of normal lung structures, thus one has to be careful in distinguishing prominent blood vessels from interstitial disease. To avoid this misinterpretation, mild to moderate edge enhancement is required for better visualization of interstitial disease. Due to smaller size of digital radiograph there is a definite learning curve to adjust to digital radiograph and one may have to interpret the film from a closer distance. Numerous observe performance studies have shown that digital radiography can equal conventional film radiography in virtually any specific task. However, for this, post processing of the digital image is required to match the digital radiograph to the task. A problem inherent in all forms of

4  Techniques, Normal Anatomy and Basic Patterns in Chest Diseases digital manipulation is that enhancement of the image for one purpose, degrades it for another. There have been conflicting reports about whether digital chest radiography can be satisfactorily interpreted on high resolution television monitors, as distinct from laser printed films. Recent studies suggest that 2 K × 2 K monitors may be adequate for making primary diagnosis on digital chest radiograph.

RADIOGRAPHIC PROJECTIONS Posteroanterior View (PA View) The most satisfactory and standard radiographic view for evaluation of the chest is posteroanterior view with patient standing (Figure 1.1). Visualization of lungs is excellent because of inherent contrast of the tissues of the thorax. The diagnostic accuracy of chest disease is partly related to the quality of radiographic images. It is incumbent on all radiologists to ensure that images on which their diagnostic impression is based are of the highest quality. Careful attention to several variables is necessary to ensure such quality. Patient Positioning Positioning must be such that the X-ray beam is properly centered, the patient’s body is not rotated, and the scapulas are rotated sufficiently anteriorly so that they are projected away from the lungs. On properly centered radiographs, the medial ends of the clavicles are projected equidistant from the margins of the vertebral column.

Figure 1.1: Normal chest X-ray PA view in standing position

Patient Respiration Respiration must be fully suspended, preferably at total lung capacity (TLC). It has been shown that in erect chest radiographs, normal subjects routinely inhale to approximately 95 percent of TLC without coaxing;15 thus, such radiographs can be of value in estimating lung volume and, by comparison with subsequent radiographs in appreciating an increase or decrease in volume as a result of disease. Film Exposure Exposure factors should be such that the resultant radiograph permits faint visualization of the thoracic spine and the intervertebral disks on the PA radiograph so that lung markings behind the heart are clearly visible. Exposure should be as short as possible, consistent with the production of adequate contrast. Unfortunately, all too frequently technical factors are such that optimal radiographic density is achieved over the lungs generally but without adequate exposure of the mediastinum or the left side of the heart, a tendency that seriously limits radiological interpretation, moderate overexposure can be easily compensated for by bright illumination; underexposure on the other hand cannot be compensated for by any viewing technique and since it prevents visualization of vital areas of the thorax, should not be tolerated in any circumstances. With perseverance, it is always possible to overcome problems of underexposure. For a PA chest radiograph, the mean radiation dose at skin entrance should not exceed 03 mGy per exposure and the exposure time should not exceed 40 msec.16 An optimally exposed radiograph presents the lung at a mid gray level (average optical density, 1.6 to 1.9). (Optical density is a measurement of the ability of the film to stop light (film blackness), and it is equal to the logarithm of light incident on the film over light transmitted by the film (D = log IO/It). The focal film distance should be at least 180 cm (72 inches) to minimize magnification16 (Focal film distance is the distance between the focal spot of the X-ray tube and the radiograph). Kilovoltage A high kilovoltage technique appropriate to the film speed should be used;10 for PA and lateral chest radiographs, the recommended kVp is 115 to 150 kVp. Since the coefficients of X-ray absorption of bone and soft tissue approximate each other in the higher kilovoltage ranges, radiographic visibility of the bony thorax is reduced with only slight change in

Chest X-ray: Techniques and Anatomy  5 the overall visibility of lung structures. Furthermore, the mediastinum is better penetrated, thereby permitting visibility of lung behind the heart and the many mediastinal lines and interfaces whose identification is so important to the overall assessment of both the mediastinum and lungs. This technique can produce chest radiographs superior in all respects to those obtained with other techniques in addition to better penetration of the mediastinum. High kilo-voltage also results in lower radiation exposure than does lower kilo-voltage. The only drawback of the high kilovoltage techniques is the diminished visibility of calcium that results from the lower coefficient of X-ray absorption; however this shortcoming has not proved troublesome in practice. Grids and Filters When using a grid, at least a 10:1 aluminum interspace grid with a minimum of 103 lines per inch recommended by the American College of Radiology.16 An alternative option uses an air gap technique in which a space of 15 cm (6 inches) is interposed between the patient and the X-ray.17 Since the air gap reduces radiation scatter by distance dispersion, no grid is required. When this technique is used a constant focal film distance of 10 feet is recommended. In a comparative study of air gap and grid techniques, it was shown that the former can provide contrast equal to those obtained with grids;18 of the various combinations of distances possible. A focal distance of 10 feet with an air gap of 6 inches provides a good compromise. Patient exposure with an air gap technique was comparable to a no-grid, no-air gap technique and was less than that obtained with a grid.

of aerated lung overlying the spine. Both diaphragms are visible throughout their length except the left anteriorly where it merges with the heart (Figure 1.2). The diaphragm of the side closer to the film is also more sharply defined. The ribs of the side away from the film appear wider.

Anteroposterior View (AP View) This is sometimes the only projection that is possible in very sick patients and usually it is obtained in wards and ICUs with portable X-ray machines. The quality is usually poor. In this view the scapulae cannot be projected out of the lung fields. The ribs and clavicle are more horizontal and the heart is magnified as compared to the PA view (Figure 1.3). AP view is sometimes very helpful in deciding whether a small questionable pulmonary opacity on the PA view is genuine, by altering its relationship to the overlying ribs and vascular shadows.20 It is also useful in differentiating free and loculated pleural fluid.

Decubitus View The cross-table lateral decubitus views are helpful in determining the confines of the cavity and demonstrating small pneumothorax or pleural effusions. The dependant hemidiaphragm normally rises considerably in this view.

Lordotic View This view is obtained either with patient leaning backward in lordotic position or more commonly, with cranial tilt of the

Lateral View The lateral view is the most important supplement to standard PA chest radiograph since much of the lung and mediastinum is hidden on the PA film. Right or left lateral view, depending on the area of interest closer to the film is obtained. The lateral view helps in localization of different lobes and segments and often this is the only view that will provide this information.19 Important observations on lateral film of the chest include the clear spaces, vertebral translucency and outline of diaphragms. There are two spaces of increased translucency where both lungs lie closest. These are retrosternal and retrocardiac areas. Retrosternal space normally measures less than 3 cm at its widest point. Vertebral bodies normally are progressively more translucent caudally because of increase in the volume

Figure 1.2: Right lateral X-ray of normal chest

6  Techniques, Normal Anatomy and Basic Patterns in Chest Diseases preferred to lateral views in case of bilateral disease since the superimposition of two lungs is significantly obviated (Figure 1.5). The left posteroanterior oblique view is particularly useful for better demonstration of trachea and its divisions.

SPECIAL RADIOGRAPHIC TECHNIQUES Inspiratory-Expiratory Radiography

Figure 1.3: Anteroposterior view (AP) view of chest. The clavicle and ribs are more horizontal in position

X-ray tube. It is particularly useful for clear demonstration of lung apices. It is important in confirming middle lobe and lingular abnormalities. The clavicles are projected above the lung fields and anterior and posterior parts of the ribs usually overlap each other (Figure 1.4). The lower chest is highly distorted in this view.

Oblique View Right or left posterior oblique views are obtained with degree of obliquity best determined with fluoroscopy. These are

Figure 1.4: Lordotic view of chest. The clavicles are projected superior to apex

Comparison of radiographs exposed in full inspiration and maximal expiration may supply useful information in two specific situations. The main indication is the investigation of air trapping, either general or local. The former is exemplified by asthma or emphysema. In both these abnormalities, diaphragmatic excursion is reduced symmetrically and lung density changes little between expiratory and inspiratory radiographs to demonstrate these features convincingly, expiration must be forced and preferably timed. When air trapping is local as in bronchial obstruction or lobar emphysema, the expiratory radiograph reveals decreased ipsilateral diaphragmatic elevation, a shift of the mediastinum toward the contra lateral hemithorax and relative absence of density change involved broncho-pulmonary segments. The second indication for expiratory-inspiratory radiography is when pneumothorax is suspected and the visceral pleural line is not visible on the standard inspiratory radiograph or the findings are equivocal. In these situations, a film taken in full expiration may show the line more clearly.

Figure 1.5: Right oblique view of normal chest

Chest X-ray: Techniques and Anatomy  7 Valsalva and Müller Maneuvers The Valsalva and Müller maneuvers respectively consisting of forced expiration and inspiration against a closed glottis may aid in determining the vascular or solid nature of intra thoracic masses. A change in size indicates a vascular lesion. Lack of change in size, however, is not helpful because it may occur with solid lesions or with insufficient effort. Although potentially helpful these maneuvers are seldom used in clinical practice.

Bedside/Portable Radiography The number of requests for radiographic examination of the chest with a mobile apparatus at a patient bedside has increased enormously since its introduction owing partly to the growth of Intensive Care Units (ICUs) and partly to the introduction of complex cardiovascular surgical procedures that require close post operative surveillance. Such radiographs are almost invariably technically inferior to those obtained in the standard manner in the radiology department itself. This inferior quality derives from multiple factors, some of which are uncontrollable (e.g. the patient’s supine position, a short focal film distance and the restricted ability of many such patients to suspend respiration or to achieve full inspiration). Other factors, however, including the technical ones used in the exposure, are subject to control.21 Frequently, these radiographs are over exposed or under exposed, sometimes to a degree that limits or even precludes recognition of the subtle changes that are so important in the radiologist either accepting an inferior product or arranging a repeat examination, with associated patient discomfort, increased radiation exposure and increased cost. Some of these problems can be minimized by using a wide latitude screen film combination. An alternative technique that is rapidly replacing the screen film combination for bedside radiographs is digital radiography since it allows satisfactory images to be obtained over a wide range of X-ray exposures. From the various studies in the literature it seems reasonable to conclude that daily routine chest radiographs are indicated in ICU patients with acute cardiac or pulmonary problems, in patients receiving mechanical ventilation, patients admitted for cardiac monitoring, or ICU patients admitted because of extra thoracic disease. Chest radiographs are recommended after insertion of endotracheal tubes, central venous lines, chest tubes and intra aortic balloons.22-24

NORMAL ANATOMY ON CHEST X-RAY The normal roentgen anatomy of the chest as seen on chest radiographs can be described in following headings.

Trachea Trachea is a straight tube, midline in the upper part and deviates slightly to the right around the aortic knuckle. It shortens and deviates more to right on expiration. Its caliber is even with decreasing translucency as it is traced caudally. On plain chest radiograph the upper limits of coronal diameters in adults are 21 mm (in females) and 25 mm (in males); sagittal diameters are 23 mm (in females) and 27 mm (in males).25 The right tracheal margin (right paratracheal stripe) can be traced down to the right main bronchus. It is 4 mm or less in thickness and measured above the azygos vein.26 The left paratracheal line is rarely visualized. After the age of 40 years, calcification of the cartilage rings of the trachea is a common finding.27 The enlarged azygos vein, which lies in the angle between the right main bronchus and trachea, may be normally seen as a round opacity in the tracheobronchial angle in the supine chest film.

Tracheobronchial Divisions The trachea divides into right and left main bronchus usually at D5 or D6 level in adults. The left main bronchus is longer and has more acute angle with trachea as compared to right main bronchus. The right main bronchus divides into upper lobe bronchus and bronchus intermedius. The upper lobe bronchus divides into apical, posterior and anterior segmental bronchi. The bronchus intermedius divides into middle and lower lobe bronchi. Middle lobe bronchus has medial and lateral branches. The lower lobe bronchus has five branches; each for superior, anterior, lateral, posterior and medial basal segments of lower lobe. Absence of middle lobe on left side modifies the bronchial division on left side. The left main bronchus divides into upper and lower lobe bronchi. The upper lobe bronchus has two divisions; the upper division divides into apico-posterior and anterior branches to supply upper lobe, the lower division supplies the lingula with superior and inferior branches. The lower lobe bronchus on left side divides similar to the right side except the absence of separate medial basal branch. Major tracheobronchial divisions are illustrated in the Figures 1.6A and B.

8  Techniques, Normal Anatomy and Basic Patterns in Chest Diseases

1

A

Figure 1.7: Line diagram showing the position of major fissure on lateral chest radiograph (Reproduced with permission)

5 cm behind the costophrenic angle on the left and just behind the angle on the right side28(Figure 1.7). The right lung has an additional fissure, the minor (horizontal) fissure. It can be drawn on chest PA film from right hilum to the sixth rib in axillary line (Figure 1.8). It separates the middle lobe from right upper lobe. There are some accessory fissures, which are occasionally seen. The azygos lobe fissure, so called because it contains the azygos vein on right and hemiazygos vein on left within its lower margin, B Figures 1.6A and B: Diagrammatic representation major tracheobronchial division as seen on frontal (A) and lateral (B) orientation: (1-apical, 2-posterior and 3-anterior segments of upper lobe; 4-lateral segment of middle lobe/superior lingula, 5-medial segment of middle lobe/inferior lingula, 6-superior, 7-medial basal, 8-anterior basal, 9-lateral basal and 10-posterior basal segments of lower lobe)

Lungs The lungs are divided into three lobes on the right side and two lobes on the left side by the interlobar fissures. The major (oblique) fissures on both sides are similar. It runs obliquely forwards and downwards (upper portion facing forward and laterally and the lower portion facing backward and medially), passing through the hilum. On a lateral view, it starts at the level of fourth or fifth thoracic vertebra to reach the diaphragm

Figure 1.8: Line diagram showing the position of minor fissure on PA chest radiograph (Reproduced with permission)

Chest X-ray: Techniques and Anatomy  9 is commonly seen on the right side with an incidence on 0.4 percent.28 It appears as a hairline with slight lateral convexity running across the right upper zone to end in a comma like expansion (azygos vein) near the hilum. The azygos lobe is the area of the lung medial to the azygos fissure. The left sided horizontal fissure, similar to the minor fissure on the right, separates the lingular from the other upper lobe segments. The superior accessory fissure separates the apical from the basal segments of the lower lobes. The inferior accessory fissure separates the medial basal from the other basal segments.

Bronchopulmonary Segments Bronchopulmonary segments of individual lobes are based on the subdivisions of lobar bronchi. These segments represent the volume of the lung, which is supplied by an integral and relatively constant segmental bronchus and blood vessels. The

boundaries between various segments are complex and with the rare exception of accessory fissure, the segments are not divided by septae. Although many pathological process may predominate in one segment or another, these usually never confirms precisely to whole of just one segment since collateral air drift occur across segmental boundaries. However, information of segmental involvement in disease process is particularly important to surgeons since these segments can be removed separately. These bronchopulmonary segments are designated as per the divisions of segmental bronchi. There is lot of overlap of bronchopulmonary segments on a PA view of chest but they project separately on a lateral view. Their approximate location as seen on frontal and lateral radiographs is illustrated (Figures 1.9A to D). The radiographic density of the two lungs is symmetrical on a well-taken PA film. If the patient is rotated, the hemithorax

Figures 1.9A to D: Line diagram showing approximate locations of various bronchopulmonary segments. A. upper and middle lobe/lingula on PA projection, B. Lower lobe on PA projection, C. Right lung on lateral projection, D. left lung on lateral projection (key same as figure 1.6)

10  Techniques, Normal Anatomy and Basic Patterns in Chest Diseases closer to the film appears more radiodense. Both PA and lateral views are necessary to localise a lesion in one or more of the pulmonary segments. Since the normal bronchi are not visualised in the peripheral lung fields, it is difficult to make out the boundary of different pulmonary segments on plain radiographs of the chest.

Hilum and Pulmonary Vasculature The structures contributing to the formation of the hilum are the pulmonary arteries and their main branches, upper lobe pulmonary veins, the major bronchi and lymph glands. Of all the structures in the hilum, only the pulmonary arteries and upper lobe veins significantly contribute to the hilar shadows on a plain radiograph. Normal lymph nodes are not seen. The left hilum is usually 0.5 to 2 cm higher than the right. Both hila are of equal density and size with a concave lateral border on PA film. The diameter of the normal descending branch of right pulmonary artery is between 10-16 mm in males and 9-15 mm in females. The course of the pulmonary vessels can be described by dividing them into three zones depending upon their positions in the lungs, i.e. hilar, mid lung and peripheral. Mid lung vessels extend from hilum upto 2 cm from the chest wall. Peripheral vessels are present in other 2 cm of the lung fields and these are rarely seen on a normal chest radiograph. The pulmonary veins have fewer branches and are straighter. The distinction between intrapulmonary arteries and veins is difficult and seldom useful so that they are collectively referred to as pulmonary vasculature. The pulmonary vessels taper gradually as they proceed peripherally. On erect PA chest radiographs; the upper zone vessels are comparatively narrower than lower zone vessels because of the effect of gravity. The bronchial vessels are normally not seen on chest radiograph.

hemidiaphragm. The bracheocephalic (innominate) vessels, superior vena cava and right atrium form the right mediastinal border. Rarely a dilated aorta may also contribute. The left border is formed by left subclavian artery, aortic knuckle, left atrial appendage and left ventricle. The radiological division of the mediastinum can be ascertained on a lateral chest radiograph by two imaginary lines (Figure 1.10). The first line is drawn from the diaphragm upward along the posterior border of heart and anterior border of the trachea into the neck. A second line is drawn connecting a point on each thoracic vertebra, 1cm behind their anterior borders. The anterior mediastinum is in front of the first line, the middle mediastinum is between the two lines and the posterior mediastinum is behind the second line. The anterior mediastinum contains thymus, heart with pericardium, great vessels and occasionally, aberrant thyroid. Middle mediastinum contains trachea and oesophagus. Nerve roots and descending thoracic aorta are the main contents of posterior mediastinum. Normal lymph nodes and adipose tissue is seen in all divisions of mediastinum. Conventional PA and lateral views of the chest are the first radiological investigation in any suspected mediastinal abnormality. However, a lesion may not be detected if it is not large enough to cause contour abnormality in the lung-mediastinum interphase. In neonates and young children the normal thymus is seen as a triangular sail shaped structure with well-defined borders, sometimes wavy in outline. Its borders project from one or both sides of the mediastinum.

Pleura Normal pleura is not visible on chest radiographs. The mediastinal surface of the pleura can occasionally be demonstrated near the midline in a well-penetrated chest radiograph.

Mediastinum It is a space lying between two lungs. It is bounded by sternum anteriorly, dorsal spine posteriorly and pleural sacs on both sides. The borders of the heart and mediastinum are clearly defined except where the heart is in contact with the left

Figure 1.10: Line diagram showing radiological divisions of the mediastinum (Reproduced with permission)

Chest X-ray: Techniques and Anatomy  11

Mediastinal Lines and Interfaces

CONCLUSION

As the two lungs approximate anteriorly, four layers of pleura and anterior mediastinum separate them forming a septum called as anterior junctional line. On PA film this line is oriented from upper right to lower left of the sternum. Similarly, posterior junctional line is produced by the posterior approximation of the lungs behind the oesophagus and anterior to spine. On PA film, the posterior junctional line usually projects through the air column of trachea. Adjacent to the vertebral bodies runs the para spinal lines. Azygoesophageal recess is formed by contact of right lower lobe with esophagus and azygos vein. The recess is frequently identified on a well-penetrated PA film as an interface that extends from the diaphragm below to the azygos arch above. Typically, it is seen as a continuous arch concave to the right. It may be straight in young adults.28 The paraspinal lines are usually 1 to 2 mm wide on PA film.

Chest radiography still remains the first investigation in the diagnosis of various chest diseases. Knowledge of normal anatomy has utmost importance in proper diagnosis of disease process on chest X-ray. Conventional radiograph may have technical limitation in some situations like critically ill patients in ICU; however, recent advances in electronics and computer technology have resulted in development of digital imaging which improves diagnostic quality of chest imaging.

Heart



Normally two thirds of the cardiac shadow lies to the left of the midline and one-third to the right. In normal individuals, the transverse diameter of the heart on PA film is usually in the range of 11.5 to 15.5 cm. It is less than 11.5 cm in about 5 percent of people and only rarely exceeds 15.5 cm in heavy, stocky individuals. Assessment of cardiac size by determining cardiothoracic ratio is more useful. Cardiothoracic ratio of 50 percent is accepted widely as the upper limit of normal, however, it exceeds 50 percent in at least 10 percent of normal individuals.29 The cardiothoracic ratio may be upto 60 percent in neonates.30

REFERENCES





Diaphragm In most individuals it has a smooth dome shape. The peak or the highest point of the dome is medial. Flattening of the dome can be measured on PA view by dropping a perpendicular from mid point of the dome to the line connecting costophrenic and cardiophrenic angles of the same side. The distance is normally greater than 1.5 cm.31 In approximately 90 percent of normal individuals, the right hemidiaphragm is 1.5 to 2.5 cm higher than the left. In rest, either the domes are at the same level or the right diaphragm may be at the slightly higher level. The discrepancy in the levels of the diaphragms is related to the position of the cardiac apex and not to the position of the liver. A difference greater than 3 cm in the levels of two hemidiaphragms is significant.32









1. Fraser RS, Muller NL, Colman N, et al. The normal lung. In: Fraser RS, Muller NL, Colman N, Pare PD (Eds) Diagnosis of Diseases of Chest 4th edition, Philadelphia: WB Saunders Co 1999;299. 2. MacMohan H, Vyborny C. Technical advances in chest radiography. AJR 1994;163:1049-59. 3. Bunch PC. Performance characteristic of asymmetric zerocross over screen film system. SPIE Proc Med Imaging IV 1992;1653:46-65. 4. Swension SJ, Grey JE, Brown LR, et al. A new asymmetric screen film combination for conventional chest radiology: evaluation of 50 patients AJR 1993;160:483-86. 5. Chotas HG, Floyd CE jr, Ravin CE. Film based chest radiography: AMBER Vs asymmetric screen film system. AJR 1993;161:743-47. 6. Hansell DM. Technical consideration. In peter Armstrong, Alam G. Wilson, Paul Dee, David M Hansell (Eds): Imaging of diseases of chest (2nd ed) Mosby 1995;1-14. 7. Neitzei U, Maack I, Gunther-Kohfahl S. Image quality of digital chest radiography system based on selenium detector. Med Phys 1994;21:509-16. 8. Chotas HG, Floyd CE jr, Ravin CE. Memory artifact related to selenium based digital radiography system. Radiology 1997;203:881-83. 9. Samei E, Flynn MJ. An experimental comparison of detector performance for direct and indirect digital radiography system. Med Phys 2003:30:608-22. 10. Samei E. Performance of digital radiography detectors: factors affecting sharpness and noise. In: Samei e. Flynn MJ. eds 2003 syllabus: categorical course in diagnostic radiology physicsadvances in digital radiography. Oak Brook, III: Radiological Society of North America 2003:49-61. 11. Abe H, MacMahon H. Engelmann R, et al. Computer aided diagnosis in chest radiography: results of large scale observer tests at the 1996-2001 RSNA scientific assemblies. Radiographics 2003:23:255-65. 12. Okazaki H, Nakamura K, Watanabe H, et al. Improved detection of long cancer arising in diffuse lung diseases on chest radiographs using temporal subtraction. Acad Radiol 2004:11:498-505. 13. Dobbins JT 3rd. Godfrey DJ. Digital X-ray tomosynthesis: current state of the art and clinical potential. Phys Med Biol 2003:48:R65-R106.

12  Techniques, Normal Anatomy and Basic Patterns in Chest Diseases 14. Godfrey DJ. McAdams HP. Dobbins JT 3rd. Optimization of the matrix inversion tomosynthesis (MITS) impulse response and modulation transfer function characteristics for chest imaging. Med Phys 2006:33:655-67. 15. Crapo RA, Montague T, Armstrong J. Inspiratory lung volume achieved on routine chest films. Invest Radiol 1979;14:137. 16. American college of Radiology: ACR standard for the performance of pediatric and adult chest radiography. American College of Radiology, Reston, VA, 1997:27. 17. Jackson FI. The air gap and improvement, and an improvement by anteroposterior positioning for chest roentgenography. Am J Roentgenol 1964;92:688. 18. Trout RD, Kelly JP, Larson VL. A comparison of air gap and grid in roentgenography of the chest. Am J Roentgenol 1975;120:404. 19. Felson B. The roentgen work-up. In Felson B (Ed) Chest Roentgenology. Philadelphia: WB Saunders Co 1, 1988. 20. Flower CDR, Armstrong P. Techniques. In: Graingern RG, Allison D (Eds). Diagnostic Radiology. 3rd edition. New York: Churchill Livingstone 1997;201. 21. Wandtke JC. 1994;190:1.

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23. Gray P, Sullivan G, Ostryzniuk P, et al. Value of postprocedural chest radiographs in the adult intensive care unit. Crit Care Med 1992;20:1513. 24. Hill JR, Horner PE, Primack SL. ICU Imaging. Clin Chest Med 2008;29(1):59-76,vi. 25. Breatnach E, Abbott GC, Fraser RE: Dimensions of the normal human trachea. AJR 1984;142:903-06. 26. Savoca CJ, Austin JHM, Goldberg HI. The right paratracheal stripe. Radiology 1977;122:295. 27. Murfitt J. The normal chest: Methods of investigation and differential diagnosis. In Sutton D (Ed): Textbook of Radiology and Medical Imaging, 4th edition. Churchill Livingstone 1987;2:326-67. 28. Mukherjee S, Gupta R. Imaging in chest diseases. In: Pande JN (Ed): Respiratory Medicine in the Tropics. 1st edition. Delhi, Oxford University Press 1998;90. 29. Muller NL. The normal chest. In: Muller NL, Fraser RS, Colman NC (Eds): Radiologic Diagnosis of Diseases of the Chest. 1st edition. Philadelphia: WB Saunders Company, 1, 2001. 30. Edwards DK, Higgins CB, Gilpin EA: The cardio-thoracic ratio in newborn infants. AJR 1981;136:136. 31. Lennon FA: Simon 6. The height of the diaphragm in the chest radiographs of normal subjects. Br J Radiol 1965;38:937. 32. Flower CDR, Verschakelan JA. The diaphragm. In: Grainger RG, Allison D (Eds). Diagnostic Radiology. 3rd edition. New York: Churchill Livingstone 1997;270.

2

MDCT Chest: Techniques and Anatomy Deep Narayan Srivastava, Atin Kumar, Shivanand Gamanagatti

INTRODUCTION AND TECHNIQUES Posteroanterior and lateral chest radiographs, together form the initial imaging modality to evaluate chest pathology. Computed tomography (CT) is however being increasingly used, as important adjunct to plain films for detection, diagnosis, and characterization of lung and mediastinal disease.

COMPUTED TOMOGRAPHY The introduction of spiral (helical) computed tomography (CT) in the early 1990s constituted a fundamental evolutionary step in the ongoing refinement of CT imaging, replacing the discontinuous acquisition of data in conventional CT with volumetric data acquisition. In 1998 several CT manufacturers introduced Multi Detector CT (MDCT) systems, which provided considerable improvement in data acquisition speed and longitudinal resolution, and more efficient use of X-rays.1-3 These systems typically offered simultaneous acquisition of four sections with a gantry rotation time of 0.5s. Since then, there has been further rapid improvement in scanner performance with increased numbers of detector rows and faster tube rotation; currently, systems with 16, 32, 40, 64, 128, 256 and 320 active detector rows are available. Rotation times of the X-ray tubes have decreased from 0.5s to 0.33s per rotation and even less. The faster data acquisition enables not only better coverage in a single breath-hold, but also results in a significant reduction in patient movement artifacts. In pediatric practice this has meant less frequent need for sedation.4 The introduction of MDCT has expanded the clinical indications for CT.

Indications for CT of the Chest In the acute setting, • Chest trauma

• Evaluation of acute aortic syndromes (dissection, transection) • Demonstration of pulmonary embolism • Identification of complications post thoracic surgery (mediastinal haematomas, complex pleural collections) In the nonacute setting, • Further evaluation of nodules, hilar or mediastinal masses identified on a chest radiograph • Lung cancer diagnosis and staging • Assessment of congenital anomalies of the thoracic great vessels • Characterization of interstitial lung disease • Identification of bronchiectasis/small airways disease • Detection of pulmonary metastases from known extrathoracic malignancy With MDCT systems, different section widths are achieved by collimating and adding together the signals of neighbouring detector rows. The Somatom Sensation 4 system, for example, uses the adaptive array detector design and has eight detector rows. Their widths in the longitudinal direction range from 1 to 5 mm at the iso centre and this arrangement allows the following collimated section widths: two sections at 0.5 mm, four at 1 mm, four at 2.5 mm, four at 5 mm, two at 8 mm and two at 10 mm. Currently, there is a trend amongst thoracic radiologists towards acquiring high-resolution (1–1.25 mm thickness) volumetric images which can then be reconstructed at 1.25–5 mm intervals for interpretation depending on the clinical question. Hence, from the same dataset, both narrow sections for high spatial resolution detail or three-dimensional (3D) post-processing, and wide sections for better contrast resolution or quick review, can be derived. The convenience of a single protocol is particularly useful for patients with suspected focal and interstitial lung disease.

14  Techniques, Normal Anatomy and Basic Patterns in Chest Diseases Thin section reconstructions are recommended for volumetric assessment and characterization of pulmonary nodules, the evaluation of interstitial lung disease and the evaluation of pulmonary embolism, whereas 3–5 mm reconstructions are usually adequate for the initial assessment of mediastinal masses and for lung cancer staging studies. In younger patients, however, a more critical approach should be adopted with the CT examination being tailored to the specific clinical question being asked, to avoid unnecessary radiation dose.5-7 With the introduction of 16- and 64- detector, 128 and 256 MDCT systems has allowed the goal of truly isotropic imaging. Isotropic imaging means, each image data element i.e. voxel is of equal dimensions in all three spatial axes, and forms the basis for image display in any arbitrarily chosen imaging plane. The acquisition of volumetric high-resolution data has particularly revolutionized the noninvasive assessment of vascular disease in the chest. Many anatomical features of the chest do not conform to a single two-dimensional (2D) axial plane and full exploitation of isotropic MDCT data requires 2D and 3D postprocessing techniques to exploit the added advantage of improved z-axis resolution and coverage. Various post processing techniques and their clinical applications are mentioned in Table 2.1.

Definition of Spiral Pitch An important parameter for characterizing helical CT is the pitch, which according to International Electrotechnical Commission specifications, is defined as p = TF/W, where TF is the table feed per rotation and W is the total width of the collimated beam.8 With four sections at 1 mm collimation and a table feed of 6 mm per rotation, the pitch is p = 6/(4 × 1) = 1.5. This definition holds true for both single- and multidetector row CT systems. In the early days of four-detector CT, the term detector pitch was introduced, which accounted for the width of a single section in the denominator. For the sake of uniformity, the term detector pitch should no longer be used.9 Faster table speed for a given collimation, resulting in a higher pitch, is associated with a reduced radiation dose (if other data acquisition parameters, including tube current, are held constant) because of a shorter exposure time. There is one disadvantage of using a higher pitch is that there is interslice gap, which may result in missing of smaller lesions (Figures 2.1A to C).

Figures 2.1A to C: Line diagram showing the value of different pitches. With smaller the pitch (C) there is overlap of slices and with higher pitch there is increase in interslice gap (A)

Dose Considerations Despite the undisputed clinical benefits of MDCT, there is the issue of increased radiation compared to single-detector CT to consider. In a CT X-ray tube, a small area on the anode plate emits X-rays that penetrate the patient and are registered by the detector. A collimator between the X-ray tube and the patient, the pre-patient collimator, is used to shape the beam and establish the dose profile. In general, the collimated dose profile is a trapezoid in the longitudinal direction. In the umbral region, X-rays emitted from the entire area of the focal spot fall on the detector; however, in the penumbral regions, only a part of the focal spot illuminates the detector—the pre-patient collimator blocking off other parts. With singledetector CT, the entire trapezoidal dose profile can contribute to the detector signal, and thus the relative dose utilization of a single-detector CT system can be close to 100 percent. With MDCT, only the plateau region of the dose profile is used to ensure an equal signal level for all detector elements. The penumbral region is then discarded, either by a post-patient collimator or by the intrinsic self-collimation of the MDCT, and represents ‘wasted’ dose. The relative contribution of the penumbral region decreases with increasing section width and with an increasing number of simultaneously acquired images. Thus, the relative dose utilization with four-section 1 mm collimation CT is 70 percent or less depending on the scanner type, whereas with 16-section CT systems, dose efficiency can be improved to 84 percent.

MDCT Chest: Techniques and Anatomy  15 The CT parameters that affect radiation dose include gantry geometry, tube current and voltage, acquisition modes, collimation, pitch and gantry rotation time. Reduction in tube current is the most practical means of reducing CT radiation dose. A 50 percent reduction in tube current can halve effective radiation dose.10 It has been suggested that in MDCT, it is possible to reduce tube current markedly (to between 40 and 70 mAs) in chest examinations without affecting image quality.11,12 On a 64-detector MDCT, the dose for a volumetric high-resolution (1 mm sections) acquisition of the thorax in a 70 kg adult can be as low as 3.6 mSv if parameters of 120 kVp and 90 mAs (pitch of 1) are used.11,12 In lung cancer screening examinations, tube current can be remarkably low and yet yield images of diagnostic quality. It has been shown that images obtained at an effective tube current of 20 mAs are of equal diagnostic utility to those obtained at 50 mAs for the detection of 6 mm simulated nodules.13

Another recommendation comprises acquisition of the entire chest using a 1 mm collimation (MDCT) at 120 kVp and 10–40 mAs depending on the body habitus of the individual.14 At a tube current of 10 mAs, the effective radiation dose is 0.27 mSv; equivalent to just five conventional PA chest radiographs. In the pediatric population, some institutions favour the use of 1 mAs/kg for imaging the thorax; an approach that significantly reduces radiation dose (Figures 2.2A to D). Tube potential (peak voltage) determines the incident X-ray mean energy, and variation in tube potential causes a substantial change in CT radiation dose. The effect of tube voltage on image quality is complex, since it affects both image noise and tissue contrast. Thus, the image quality ramifications of a decrease in tube voltage to reduce radiation exposure must be carefully examined before being implemented. For chest examinations, 120 kVp is commonly

Figures 2.2A to D: Axial CT of a child with solitary intrapulmonary metastasis from Osteosarcoma. Standard-dose CT technique (175 mAs) in lung and mediastinal window settings (A and B). Follow-up CT using low-dose technique (25 mAs), demonstrating the growth of the metastasis (C and D). A significant increase in noise can only be observed in the mediastinal window settings

16  Techniques, Normal Anatomy and Basic Patterns in Chest Diseases used. In thin patients (