Duke Review of MRI Physics: Case Review Series [2 ed.] 9780323530385, 0323530389

Table of contents :
IFC
Duke Reviewof MRI Physics: CASE REVIEW SERIES
Series Editor
Volumes in the CASE REVIEW Series
Duke Reviewof MRI Physics: CASE REVIEW SERIES
Copyright
Dedication
CONTRIBUTORS
SERIES FOREWORD
PREFACE
CONTENTS
1 - T1 Contrast
Case Answers
Basic Spin Principles and T1 Relaxation
T1 Contrast and Pulse Sequence Considerations
Spin Echo
Gradient Recalled Echo
Clinical Applications
Discussion
Discussion
CASE 1.2 ANSWERS
Discussion
Discussion
CASE 1.3 ANSWERS
Discussion
Diagnosis
Discussion
CASE 1.4 ANSWERS
Discussion
CASE 1.5 ANSWER
TAKE-HOME POINTS
Suggested Readings
2 - T2 Contrast
Case Answers
Basic Spin Principles and T2 Relaxation
T2 Contrast and Pulse Sequence Considerations
Spin Echo
Gradient Recalled Echo
Fat on T2-Weighted Imaging
CASE 2.2 ANSWER
Autosomal Dominant Polycystic Kidney Disease
Variable Appearance of Fluid on T2-Weighted Imaging
CASES 2.3, 2.4, AND 2.5 ANSWERS
Cavernoma With Superficial Siderosis
Appearance of Blood on T2-Weighted Spin Echo Images
CASES 2.6 AND 2.7 ANSWERS
Pivot Shift Bone Marrow Contusion
Marrow T2 Hyperintensity
CASE 2.8 ANSWER
Vasogenic Edema Secondary to Multiple Brain Metastases
Vasogenic Edema and Cytotoxic Edema
CASES 2.9, 2.10, AND 2.11 ANSWERS
MR Cholangiopancreatography
CASES 2.12, 2.13, AND 2.14 ANSWERS
Peripheral Nerve Schwannoma
Hepatic Hemangioma
T2 Hyperintense Neoplasms
CASES 2.15, 2.16, AND 2.17 ANSWER
Full-Thickness Tear of the Supraspinatus Tendon
Fibulocollateral Ligament Sprain
Physics of Low T2 Signal in Tendons and Ligaments
CASE 2.19 ANSWER
MR Appearance of Cartilage
CASE 2.20 ANSWER
Septate Uterus
Uterine Leiomyomas
Uterine Anatomy and Tight Cell Packing
CASE 2.22 ANSWER
Prostate Adenocarcinoma Invasion into the Left Seminal Vesicles
Brain Abscess With a Thin T2 Hypointense Rim
Pathology Manifesting as T2 Hypointensity
TAKE-HOME POINTS
Physics
Clinical Considerations
References
3 - Proton Density
Case Answers
Physics
Clinical Considerations
Discussion
Discussion
CASE 3.2 ANSWERS
Discussion
Discussion
CASE 3.3 ANSWERS
TAKE-HOME POINTS
Suggested Readings
4 - Gadolinium-Based Contrast Agents
Case Answers
Physics
Discussion
CASE 4.2 ANSWERS
Discussion
CASE 4.3 ANSWERS
Discussion
CASE 4.4 ANSWERS
Discussion
CASE 4.5 ANSWERS
Discussion
CASE 4.6 ANSWERS
Discussion
CASE 4.7 ANSWERS
TAKE-HOME POINTS
Suggested Readings
5 - Frequency and Spatial Saturation Pulses
Case Answers
Saturation Pulses
Discussion
CASE 5.2 ANSWERS
Discussion
CASE 5.3 ANSWERS
Discussion
CASE 5.4 ANSWERS
Discussion
CASE 5.5 ANSWER
TAKE-HOME POINTS
Suggested Readings
6 - Inversion Recovery
Case Answers
Inversion Recovery
Diagnosis
Discussion
CASE 6.2 ANSWERS
Diagnosis
Discussion
CASE 6.3 ANSWER
Diagnosis
Discussion
CASE 6.4 ANSWER
Diagnosis
Discussion
CASE 6.5 ANSWER
Discussion
CASE 6.6 ANSWERS
Diagnosis
Discussion
CASE 6.7 ANSWER
Diagnosis
Discussion
CASE 6.8 ANSWER
TAKE-HOME POINTS
Suggested Readings
7 - Type 2 Chemical Shift Artifact
Case Answers
Type 2 Chemical Shift
Hepatic Steatosis and Focal Fat Sparing
CASES 7.2 AND 7.3 ANSWERS
Hemosiderin Deposition
Signal Loss from T2* Decay
CASES 7.4 AND 7.5 ANSWERS
Angiomyolipoma and Hemorrhagic Cyst
Using the India Ink Artifact
CASES 7.6 AND 7.7 ANSWERS
Hepatocellular Adenoma
CASE 7.8 ANSWERS
Dixon Technique
Mature Cystic Ovarian Teratoma (Dermoid Cyst)
Using Fat-Water Separation Imaging
CASE 7.10 ANSWERS
TAKE-HOME POINTS
Physics
Clinical Considerations
References
8 - Susceptibility Artifact
Case Answers
Susceptibility Artifact
Discussion
CASES 8.2, 8.3, AND 8.4 ANSWERS
Susceptibility in Gradient Recalled Echo and Susceptibility-Weighted Image Sequences
Discussion
Further Considerations Regarding Susceptibility in GRE and SWI Sequences
CASE 8.5 ANSWER
Blooming Due to Susceptibility
CASE 8.6 ANSWER
Discussion
Susceptibility Effects in Relation to Time to Echo
CASES 8.7 AND 8.8 ANSWERS
Susceptibility and Fat Suppression
CASE 8.9 ANSWER
Discussion
Susceptibility With Flair Imaging
CASE 8.10 ANSWER
Discussion
Susceptibility With Diffusion Imaging
CASE 8.11 ANSWER
Susceptibility With T2-Weighted Imaging
CASES 8.12, 8.13, AND 8.14 ANSWER
TAKE-HOME POINTS
Defining Susceptibility
Methods to Reduce Susceptibility Artifact
Clinical Utility of Susceptibility Artifact
Susceptibility Artifact Interference With Diagnosis
Sequences Sensitive to Susceptibility Effects
References
9 - Motion, Pulsation, and Other Artifacts
CASE ANSWERS
Motion and Pulsation Artifact
Discussion
CASE 9.2 ANSWER
Discussion
CASE 9.3 ANSWER
Discussion
CASE 9.4 ANSWER
Discussion
CASE 9.5 ANSWER
Discussion
CASE 9.6 ANSWER
Discussion
CASE 9.7 ANSWERS
Discussion
CASE 9.8 ANSWER
Discussion
CASE 9.9 ANSWER
Discussion
CASE 9.10 ANSWER
Discussion
CASE 9.11 ANSWER
Discussion
CASE 9.12 ANSWER
TAKE-HOME POINTS
Suggested Readings
10 - Vascular Contrast
CASE ANSWERS
Vascular Contrast
Flow Voids
Flow-Related Enhancement
Entry Slice Phenomenon
Gradient Moment Nulling
Discussion
CASE 10.2 ANSWER
Discussion
CASE 10.3 ANSWERS
Discussion
CASE 10.4 ANSWERS
Discussion
CASE 10.5 ANSWER
Discussion
CASE 10.6 ANSWER
Discussion
CASE 10.7 ANSWER
Discussion
CASE 10.8 ANSWER
Discussion
CASE 10.9 ANSWERS
Discussion
CASE 10.10 ANSWER
TAKE-HOME POINTS
References
11 - Cardiac Magnetic Resonance Imaging
CASE ANSWERS
Discussion
Cardiac MRI
Black Blood Technique
White Blood Technique
Discussion
CASE 11.2 ANSWER
Discussion
CASE 11.3 ANSWERS
Discussion
CASE 11.4 ANSWERS
Discussion
CASE 11.5 ANSWER
Discussion
CASE 11.6 ANSWERS
Discussion
CASE 11.7 ANSWER
TAKE-HOME POINTS
References
12 - Time-of-Flight Imaging
Case Answers
Physics
Signal Saturation
Inflow of Unsaturated (Fresh) Protons
Limitations to Time of Flight
Additional Properties Unique to Time of Flight
Discussion
CASE 12.2 ANSWERS
Discussion
CASE 12.3 ANSWERS
Discussion
CASE 12.4 ANSWER
Discussion
CASE 12.5 ANSWER
Discussion
CASE 12.6 ANSWER
Discussion
CASE 12.7 ANSWER
TAKE-HOME POINTS
References
13 - Time-Resolved Contrast-Enhanced Magnetic Resonance Angiography
CASE ANSWERS
Time-Resolved Magnetic Resonance Angiography
k-Space Physics
k-Space Filling Techniques
Parallel Imaging
Discussion
CASE 13.2 ANSWERS
Discussion
CASE 13.3 ANSWER
Discussion
CASE 13.4 ANSWERS
Discussion
CASE 13.5 ANSWER
Discussion
CASE 13.6 ANSWER
Discussion
CASE 13.7 ANSWER
TAKE-HOME POINTS
References
14 - Phase Contrast
Case Answers
Thrombus
Phase Contrast Imaging
Conventional Two- and Three-Dimensional Phase Contrast Imaging
Four-Dimensional Phase Contrast Imaging
CASE 14.2 ANSWERS
Right Transverse and Sigmoid Sinus Thrombosis
Magnetic Resonance Venogram
CASE 14.3 ANSWERS
Chiari I Malformation
Cerebrospinal Fluid Flow
CASE 14.4 ANSWERS
Atrial Septal Defect
Flow Assessment
CASE 14.5 ANSWERS
Phase Contrast Assessment of Aortic Valve Pathology and Cardiac Flow Quantification
CASES 14.6 AND 14.7 ANSWERS
TAKE-HOME POINTS
Physics
Clinical Considerations
References
15 - Diffusion Magnetic Resonance Imaging
Case Answers
Physics
Discussion
CASE 15.2 ANSWERS
Discussion
CASE 15.3 ANSWERS
Discussion
CASE 15.4 ANSWER
Discussion
CASE 15.5 ANSWERS
Discussion
CASE 15.6 ANSWERS
Discussion
CASE 15.7 ANSWER
Discussion
CASE 15.8 ANSWER
Discussion
CASE 15.9 ANSWER
Discussion
CASE 15.10 ANSWER
Discussion
CASE 15.11 ANSWER
Discussion
CASE 15.12 ANSWER
TAKE-HOME POINTS
References
16 - Perfusion Magnetic Resonance Imaging
CASE ANSWER
Discussion
Ring Artifact
CASE 16.2 ANSWER
Discussion
Cardiac Perfusion MRI: Further Considerations
CASE 16.3 ANSWER
Brain Perfusion MRI
CASE 16.4 ANSWER
MRI Perfusion Limitations
CASE 16.5 ANSWER
Discussion
MRI Perfusion Methods
CASE 16.6 ANSWER
Discussion
Other Uses of MRI Perfusion
CASE 16.7 ANSWER
Discussion
Other Uses of MRI Perfusion
CASE 16.8 ANSWER
Discussion
CASE 16.9 ANSWER
Discussion
CASE 16.10 ANSWER
Discussion
CASE 16.11 ANSWER
TAKE-HOME POINTS
Defining Perfusion
Cardiac Perfusion Imaging
Brain Perfusion Imaging
Body Perfusion Imaging
References
17 - Magnetic Resonance Spectroscopy
CASE ANSWER
Magnetic Resonance Spectroscopy
Discussion
Normal Spectrum
CASE 17.2 ANSWERS
Astrocytoma Grading
Single-Voxel Versus Multivoxel Spectroscopy
CASE 17.3 ANSWER
Low-Grade Astrocytoma
Spectroscopy Changes With Field Strength and Time to Echo
CASE 17.4 ANSWER
Lactate Peaks
CASE 17.5 ANSWER
Acute Infarct
CASE 17.6 ANSWER
Kearns-Sayre Syndrome
CASE 17.7 ANSWER
Hypoxic-Ischemic Encephalopathy
Voxel Size in Spectroscopy
CASE 17.8 ANSWER
Primary Angiitis of the Central Nervous System
CASE 17.9 ANSWER
Krabbe Disease
Multivoxel Spectroscopy
CASE 17.10 ANSWERS
Alzheimer Disease
CASE 17.11 ANSWER
TAKE-HOME POINTS
ACKNOWLEDGMENT
References
18 - Functional Magnetic Resonance Imaging
Case Answers
Functional MRI
Wada Test and Intraoperative Cortical Stimulation
BOLD Effect and the Hemodynamic Response
Creating fMRI Images
Diagnosis
Discussion
fMRI Tasks
CASE 18.2 ANSWERS
Diagnosis
Discussion
Statistical Analysis of fMRI Data
CASE 18.3 ANSWERS
Diagnosis
Discussion
Supplementary Cortical Activation
CASE 18.4 ANSWERS
Diagnosis
Discussion
Participatory Cortical Areas
CASE 18.5 ANSWER
Diagnosis
Discussion
Susceptibility Artifact
CASE 18.6 ANSWER
Diagnosis
Discussion
Pathology Results in Alterations to the Hemodynamic Response
CASE 18.7 ANSWER
Diagnosis
Discussion
Tumors Effect on Autoregulation
CASE 18.8 ANSWER
Diagnosis
Discussion
Motion and Susceptibility Artifact Limitations
CASE 18.9 ANSWER
TAKE-HOME POINTS
References
19 - Basics of Magnetic Resonance Imaging Safety
CASE ANSWER
MR Safety
Static Magnetic Field
Direct Effects of the Static Magnetic Field
Indirect Effects of the Static Magnetic Field
ANSWERS: STATIC MAGNETIC FIELD
Magnetic Materials
Preventing Accidents Due to Magnetic Attraction
Quenching
ANSWERS: QUENCHING
Gradient Fields
Direct Effects
Indirect Effects
Radiofrequency Field
ANSWERS: SPECIFIC ENERGY ABSORPTION RATE
Discussion
Implants and MRI
CASE 19.2 ANSWERS
Discussion
Active Devices
CASE 19.3 ANSWERS
Discussion
Passive Implants
Piercings
Tattoos and Permanent Makeup
CASE 19.4 ANSWERS
TAKE-HOME POINTS
References
INDEX
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q
R
S
T
U
V
W
X
Z
IBC

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Duke Review of MRI Physics CASE REVIEW SERIES

Series Editor David M. Yousem, MD, MBA Vice-Chairman Radiology, Program Development Associate Dean, Professional Development Department of Radiology Johns Hopkins School of Medicine Baltimore, Maryland

Volumes in the CASE REVIEW Series Brain Imaging Breast Imaging Cardiac Imaging Duke Review of MRI Physics Emergency Radiology Gastrointestinal Imaging General and Vascular Ultrasound Genitourinary Imaging Head and Neck Imaging Imaging Physics Musculoskeletal Imaging Neuroradiology Non-Interpretive Skills for Radiology Nuclear Medicine and Molecular Imaging Obstetric and Gynecologic Ultrasound Pediatric Imaging Spine Radiology Thoracic Imaging Vascular and Interventional Imaging

Duke Review of MRI Physics CASE REVIEW SERIES Wells I. Mangrum, MD

Charles M. Maxfield, MD

Partner Medical X-ray Consultants LLC Eau Claire, Wisconsin

Professor Department of Radiology Duke University Durham, North Carolina

Timothy J. Amrhein, MD Assistant Professor Department of Radiology Duke University Medical Center Durham, North Carolina

Allen W. Song, PhD

Scott M. Duncan, MD

Elmar M. Merkle, MD

Partner Radiology Associates of Southern Indiana Prospect, Kentucky

Department of Radiology University Hospitals Basel, Switzerland

Phil B. Hoang, MD Staff Radiologist Department of Radiology Southeast Louisiana Veterans Health Care System New Orleans, Louisiana

Department of Radiology Duke University Durham, North Carolina

1600 John F. Kennedy Blvd. Ste 1800 Philadelphia, PA 19103-2899

DUKE REVIEW OF MRI PHYSICS: CASE REVIEW SERIES, SECOND EDITION

ISBN: 978-0-323-53038-5

Copyright © 2019 by Elsevier, Inc. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/ permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein).

Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. With respect to any drug or pharmaceutical products identified, readers are advised to check the most current information provided (i) on procedures featured or (ii) by the manufacturer of each product to be administered, to verify the recommended dose or formula, the method and duration of administration, and contraindications. It is the responsibility of practitioners, relying on their own experience and knowledge of their patients, to make diagnoses, to determine dosages and the best treatment for each individual patient, and to take all appropriate safety precautions. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. Previous edition copyrighted © 2012 by Mosby, an imprint of Elsevier Inc. Library of Congress Cataloging-in-Publication Data Names: Mangrum, Wells I., author. Title: Duke review of MRI physics / Wells I. Mangrum [and 6 others]. Other titles: Review of MRI physics | Case review series. Description: Second edition. | Philadelphia, PA : Elsevier, Inc., [2019] | Series: Case review series | Preceded by: Duke review of MRI principles / Wells I. Mangrum ... [et al.]. c2012. | Includes bibliographical references and index. Identifiers: LCCN 2018000643 | ISBN 9780323530385 (hardcover : alk. paper) Subjects: | MESH: Magnetic Resonance Imaging | Case Reports | Problems and Exercises Classification: LCC RC386.6.M34 | NLM WN 18.2 | DDC 616.07/548--dc23 LC record available at https://lccn.loc.gov/2018000643

Executive Content Strategist: Robin Carter Content Development Specialist: Meghan Andress Publishing Services Manager: Patricia Tannian Senior Project Manager: Carrie Stetz Design Direction: Amy Buxton

Printed in China Last digit is the print number:

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For my father. “Our doubts are traitors, and make us lose the good we oft may win, by failing to attempt.” Wells I. Mangrum To my wife, Jill, and to our two wonderful children, Ty and Kate. Thank you always for your unwavering support and love. The time dedicated to this book was as much your sacrifice as it was mine. Timothy J. Amrhein To my wife, Kristen: thank you so much for supporting me through this process and encouraging me to push through. To my kids, Carter, Tyler, and Chase: you all have grown so much since the first edition came out. I want you to know that you can accomplish anything in life if you work hard and put your mind to it. To Wells: once again, your persistence, vision, and hard work have made this book possible. To the Duke Radiology Department: I enjoyed my time at Duke immensely. The training I received was second to none, and there are still several occasions that I refer back to the lessons I learned during residency and fellowship. I am so very proud to be a Duke Radiology alum, and I hope this book will add to the great reputation and tradition of Duke Radiology. Scott M. Duncan To my wife, Kim Chi, and our children, Connor, Madeleine, Charles, and Maximus. Y’all are the greatest blessings of my life. Phil B. Hoang To Sharon, Charles, and Jack. And to my coauthors, for allowing me to contribute to this tremendous project. Charles M. Maxfield To my wife, Christina, the true source of my academic time, and my beloved daughters, Paula and Anna. Elmar M. Merkle

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CONTRIBUTORS TIMOTHY J. AMRHEIN, MD

ELMAR M. MERKLE, MD

Assistant Professor Department of Radiology Duke University Medical Center Durham, North Carolina

Department of Radiology University Hospitals Basel, Switzerland JEFFREY R. PETRELLA, MD

MUSTAFA R. BASHIR, MD

Associate Professor of Radiology Department of Radiology Division of Abdominal Imaging Center for Advanced Magnetic Resonance Development Duke University Medical Center Durham, North Carolina NICHOLAS T. BEFERA, MD

Fellow, Vascular and Interventional Radiology Department of Radiology Duke University Medical Center Durham, North Carolina

Professor of Radiology Division of Neuroradiology Director, Alzheimer Disease Imaging Research Lab Duke University Medical Center Durham, North Carolina NANCY PHAM, MD

Assistant Professor of Neurosurgery University of California–Davis Davis, California CHRISTOPHER J. ROTH, MD, MMCI

Partner Radiology Associates of Southern Indiana Prospect, Kentucky

Vice Chair of Radiology for IT & Informatics Duke University Director of Imaging IT Strategy, Duke Health Associate Professor of Neuroradiology Duke University Medical Center Durham, North Carolina

PHIL B. HOANG, MD

FRANCESCO SANTINI, PHD, MRSE

Staff Radiologist Department of Radiology Southeast Louisiana Veterans Health Care System New Orleans, Louisiana

Department of Radiology Division of Radiological Physics University Hospital Basel; Department of Biomedical Engineering University of Basel Basel, Switzerland

SCOTT M. DUNCAN, MD

SPENCER J. HOOD

Department of Neuroscience Brigham Young University Salt Lake City, Utah STEVEN Y. HUANG, MD

Associate Professor Department of Interventional Radiology University of Texas MD Anderson Cancer Center Houston, Texas ARI KANE, MD

Department of Radiology and Biomedical Engineering University of California–San Francisco San Francisco, California SAMUEL J. KUZMINSKI

Department of Radiological Sciences University of Oklahoma Health Sciences Center Oklahoma City, Oklahoma WELLS I. MANGRUM, MD

Partner Medical X-ray Consultants LLC Eau Claire, Wisconsin

ALLEN W. SONG, PHD

Department of Radiology Duke University Durham, North Carolina CARLOS TORRES, MD, FRCPC

Associate Professor of Radiology Department of Radiology University of Ottawa; Neuroradiologist Department of Diagnostic Imaging The Ottawa Hospital; Clinical Investigator Ottawa Hospital Research Institute OHRI Ottawa, ON, Canada NEAL K. VIRADIA, MD, MPH

Interventional Radiology Fellow Department of Radiology Division of Interventional Radiology Duke University Durham, North Carolina JAMES T. VOYVODIC, PHD

CHARLES M. MAXFIELD, MD

Professor Department of Radiology Duke University Durham, North Carolina

Department of Radiology Duke University Medical Center Durham, North Carolina

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SERIES FOREWORD I am very pleased with the evolution of the second edition of Duke Review of MRI Physics. The authors have used a theory of collective wisdom to garner the expertise of many of the great present and future minds in MRI. They think global, but act local, and cover more areas of MR physics than ever before while still keeping the case-based approach that works so well in this forum. This edition adds material on cardiac MRI and safety

considerations, is more colorful, and uses “take-home points” to make sure the readers “get it.” I got it. You should, too! Congratulations to Drs. Mangrum, Amrhein, Duncan, Hoang, Maxfield, Song, and Merkle for the incredible teamwork and wisdom they have imparted to this edition. Bravo. David M. Yousem, MD, MBA

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PREFACE This second edition improves our successful first edition. First, we have added multiple-choice questions to our cases to better fit with the current board exam format. Second, we have improved publication quality by incorporating color images into the main body of the text. Third, we have revised

every chapter with up-to-date scientific literature. Fourth, we have added new chapters on cardiac imaging and MRI safety. These changes have required hundreds of hours by many different editors and authors. We hope that you benefit from our work.

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CONTENTS

Chapter 1 T1 Contrast

1

Phil B. Hoang, Steven Y. Huang, Allen W. Song, and Elmar M. Merkle

Chapter 2 T2 Contrast

11

Samuel J. Kuzminski, Ari Kane, and Timothy J. Amrhein

Chapter 3 Proton Density

33

Charles M. Maxfield

Chapter 4 Gadolinium-Based Contrast Agents

39

Charles M. Maxfield

Chapter 5 Frequency and Spatial Saturation Pulses

49

Phil B. Hoang, Allen W. Song, and Elmar M. Merkle

Chapter 6 Inversion Recovery

55

Phil B. Hoang, Allen W. Song, and Elmar M. Merkle

Chapter 7 Type 2 Chemical Shift Artifact

65

Nicholas T. Befera, Mustafa R. Bashir, and Timothy J. Amrhein

Chapter 8 Susceptibility Artifact

77

Neal K. Viradia, Elmar M. Merkle, Allen W. Song, and Wells I. Mangrum

Chapter 9 Motion, Pulsation, and Other Artifacts

91

Phil B. Hoang, Steven Y. Huang, Allen W. Song, and Elmar M. Merkle

Chapter 10 Vascular Contrast

107

Scott M. Duncan

Chapter 11 Cardiac Magnetic Resonance Imaging

121

Scott M. Duncan

Chapter 12 Time-of-Flight Imaging

131

Scott M. Duncan

Chapter 13 Time-Resolved Contrast-Enhanced Magnetic Resonance Angiography

145

Scott M. Duncan

Chapter 14 Phase Contrast

159

Nancy Pham, Ari Kane, and Timothy J. Amrhein

Chapter 15 Diffusion Magnetic Resonance Imaging Charles M. Maxfield

171

Chapter 16 Perfusion Magnetic Resonance Imaging

187

Neal K. Viradia, Mustafa R. Bashir, Carlos Torres, Elmar M. Merkle, Allen W. Song, and Wells I. Mangrum

Chapter 17 Magnetic Resonance Spectroscopy

203

Wells I. Mangrum, Allen W. Song, and Jeffrey R. Petrella

Chapter 18 Functional Magnetic Resonance Imaging

217

Spencer J. Hood, Wells I. Mangrum, Christopher J. Roth, Allen W. Song, James T. Voyvodic, and Jeffrey R. Petrella

Chapter 19 Basics of Magnetic Resonance Imaging Safety

231

Francesco Santini and Timothy J. Amrhein

Index

xiv

243

CH A P TER 1

T1 Contrast Phil B. Hoang, Steven Y. Huang, Allen W. Song, and Elmar M. Merkle

O P E N I N G C A S E 1 .1  

A

1. In figure A, which of the following MRI parameters produces a T1-weighted sequence? A. Short time to repetition (TR), short time to echo (TE) B. Long TR, short TE C. Short TR, long TE D. Long TR, short TE

B

2. Figure B shows a patient with a clinical history of short stature. What is the most likely diagnosis? A. Craniopharyngioma B. Saccular aneurysm C. Pituitary macroadenoma D. Ectopic neurohypophysis

CASE ANSWERS O P E N I N G C A S E 1 .1 1. In figure A, which of the following MRI parameters produces a T1-weighted sequence? A. Short time to repetition (TR), short time to echo (TE) 2. Figure B shows a patient with a clinical history of short stature. What is the most likely diagnosis? D. Ectopic neurohypophysis

Discussion

A

A short TR and short TE optimize T1 contrast in a MRI image. A long TR and short TE would produce a proton density– weighted image, and a long TR and long TE would produce a T2-weighted image. A short TR and long TE sequence is not used in clinical MRI because this combination produces poor tissue contrast. The normal T1 bright spot of the neurohypophysis is due to the proteins bound to vasopressin. In this case, the neurohypophysis is not present in the posterior sella, but is instead located in the superior aspect of the pituitary stalk. Note the diminutive appearance of the stalk. These findings are most compatible with ectopic neurohypophysis.

B FIG. 1.C1. (A) Coronal and (B) sagittal T1-weighted images of the brain. A small high T1 signal focus at the superior aspect of the infundibulum (arrows) is demonstrated. Lack of the expected bright spot of the posterior pituitary gland is noted, and the pituitary stalk is abnormally small.

Basic Spin Principles and T1 Relaxation Because of its abundance in the human body, hydrogen is the most frequently imaged nucleus in clinical MRI. Hydrogen has a considerable angular magnetic moment, with its single, positively charged proton acting as a tiny spinning bar magnet. Protons normally spin in random directions in the absence of an external magnetic field; because of this random movement, the magnetic vector sum of these protons is typically zero. When placed in a strong external magnetic field (B0), these protons align parallel (low energy) or antiparallel (high energy) with respect to B0; more protons tend to align parallel to B0 because less energy is required to do so. Because they possess magnetic and angular momentum, the protons precess, or wobble, around the axis of B0 instead of spinning in a tight circle; this precession motion confers both longitudinal (μz) and transverse (μxy) components in the magnetic moments of the protons. Protons tend to precess at a certain frequency while under the influence of B0, which is called the Larmor frequency. The Larmor frequency defines the frequency at which the radiofrequency pulse is broadcast to induce proton resonance, or excitation. The Larmor frequency is defined as W = γB, where W is the Larmor frequency, γ is the gyromagnetic ratio in MHz/ tesla (T), and B is the strength of the static magnetic field in T. Thus the Larmor frequency is proportional to the strength of the 2

main magnetic field; at 1.5 T, the Larmor frequency of hydrogen protons is 63.8 MHz and approximately 127 MHz at 3.0 T. The vector sum of the magnetic moments of the precessing protons (MZ and MXY) results in a net equilibrium magnetization (M0). This magnetization vector is primarily in the longitudinal direction (MZ) because more protons align in parallel with B0. The transverse component (MXY) does not contribute significantly to M0 because the protons do not spin in phase with each other and effectively cancel each other out. As the energy of B0 increases, so does the energy differential between protons in the low (parallel) and high (antiparallel) states, with increasing numbers of protons aligning parallel to B0. This results in a significant directional (vector) component of the net magnetization. However, the receiver coil, which is the component of the MRI machine that detects signals, is sensitive only to variations of the magnetization vector; the original main net magnetization along the z direction, even though it is precessing, is viewed as a stationary vector from the receiver coil perspective. Given this, something must be done to perturb the system (i.e., tip the magnetization away from the z-axis so that the precession motion is visible) and generate detectable signal changes that can be picked up by the receiver coils. This comes in the form of a radiofrequency (RF) excitation pulse.

T1 Contrast and Pulse Sequence Considerations An important point to consider when interpreting any MR image is that image contrast is not exclusively due to differences in T1, T2, or proton density; these contrasts all make some contribution. However, by manipulating certain operator-dependent

parameters, we can have more of one contrast and less of the others. This is why we use the terms T1, T2, and proton density weighting when describing the contrast in an image.

Spin Echo In a conventional spin echo (SE) sequence, the 90-degree RF pulse is followed by a 180-degree refocusing pulse, which is administered at the halfway point of TE and is used to bring the protons back into an in-phase (i.e., synchronized) state. The parameter with the greatest effect on T1 contrast on a conventional SE sequence is TR, which is the time interval between successive excitation pulses. The TRs for T1-weighted SE sequences are typically in the range of 400 to 800 ms. As the TR lengthens, most tissues recover their longitudinal magnetization and produce signal; although this will increase overall signal-to-noise ratio in the image, it will diminish T1 contrast (Fig. 1.1). Although modifying TR can optimize T1 contrast, adjusting the length of the second parameter, the TE, governs T2 contrast. TE is the time interval between the excitation pulse and signal collection; this parameter has the greatest effect on decreasing the contribution from T2 contrast, as illustrated below. To minimize the T2 contrast so that T1 contrast is dominant, the TE should be kept as short as possible (TE = 15–25 ms). A moderate TE would generate significant T2 contrast (Fig. 1.2). 

Gradient Recalled Echo Gradient recalled echo (GRE) pulse sequences use an excitation pulse with a variable flip angle (