MRI at a Glance

138 Pages·2016·14.9 MB·English

by  Catherine Westbrook

MRI
at a Glance
Third Edition
Catherine Westbrook
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MRI
at a Glance
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MRI
at a Glance
Third Edition
Catherine Westbrook
Department of Medicine and Healthcare
Science
Faculty of Medical Science
Anglia Ruskin University
Cambridge, UK
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Library of Congress Cataloging-in-Publication Data
Westbrook, Catherine.
MRI at a glance / Catherine Westbrook. — Third edition.
pages cm
Includes index.
ISBN 978-1-119-05355-2 (pbk.)
1. Magnetic resonance imaging—Outlines, syllabi, etc. 2. Medical physics—Outlines, syllabi, etc.
I. Title.
RC78.7.N83W4795 2016
616.07′548—dc23
2015022541
A catalogue record for this book is available from the British Library.
Wiley also publishes its books in a variety of electronic formats. Some content that appears in print
may not be available in electronic books.
Cover image: © Getty Images/Yuji Sakai
Set in 9.5/11.5pt Minion Pro by Aptara Inc., New Delhi, India
1 2016
Contents
Preface vii
Acknowledgements viii
How to use your textbook ix
About the companion website xi
1 Magnetism and electromagnetism 2
2 Atomic structure 4
3 Alignment 6
4 Precession 8
5 Resonance and signal generation 10
6 Contrast mechanisms 12
7 Relaxation mechanisms 14
8 T1 Recovery 16
9 T2 decay 18
10 T1 weighting 20
11 T2 weighting 22
12 PD weighting 24
13 Conventional spin echo 26
14 Fast or turbo spin echo – how it works 28
15 Fast or turbo spin echo – how it is used 30
16 Inversion recovery 32
17 Gradient echo – how it works 34
18 Gradient echo – how it is used 36
19 The steady state 38
20 Coherent gradient echo 40
21 Incoherent gradient echo 42
22 Steady-state free precession 44
23 Balanced gradient echo 46
24 Ultrafast sequences 48
25 Diffusion and perfusion imaging 50
26 Functional imaging techniques 52
27 Gradient functions 54
28 Slice selection 56
29 Phase encoding 58
30 Frequency encoding 60
31 K space – what is it? 62
v
32 K space – how is it filled? 64
33 K space and image quality 66
34 Data acquisition – frequency 68
35 Data acquisition – phase 70
36 Data acquisition – scan time 72
37 K space traversal and pulse sequences 74
38 Alternative K space filling techniques 76
39 Signal to noise ratio 78
40 Contrast to noise ratio 80
41 Spatial resolution 82
42 Chemical shift artefacts 84
43 Phase mismapping 86
44 Aliasing 88
45 Other artefacts 90
46 Flow phenomena 92
47 Time-of-flight MR angiography 94
48 Phase contrast MR angiography 96
49 Contrast-enhanced MR angiography 98
50 Contrast agents 100
51 Magnets 102
52 Radiofrequency coils 104
53 Gradients and other hardware 106
54 MR safety – bio-effects 108
55 MR safety – projectiles 110
Appendix 1a: The results of optimizing image quality 112
Appendix 1b: Parameters and their associated trade-offs 113
Appendix 2: Artefacts and their remedies 114
Appendix 3: Main manufacturers’ acronyms 115
Glossary 116
Index 121
vi
Preface
MRI at a Glance is one of a series of books that presents analogies, bulleted lists, simple tables, key points, equations (but
complex information in an easily accessible format. This only for those who like them), scan tips, ‘Did You Know’ learning
series has become famous for its concise text and clear points, some questions and answers and plenty of images to aid
diagrams, which are laid out with text on one page and diagrams the understanding of each topic. There are appendices on trade‐
relating to the text on the opposite page. In this way all the infor- offs, acronyms, abbreviations and artefacts. The glossary has also
mation on a particular topic is summarized so that the reader has been expanded.
the essential points at their fingertips. This book is intended to provide a concise overview of essen-
The third edition has been updated with a new companion tial facts for revision purposes and for those very new to MRI.
website that includes some exciting new features. In the book, For more detailed explanations the reader is directed to MRI in
some chapters have been streamlined and reorganized and there Practice and Handbook of MRI Technique. Indeed, the diagrams
are some updated images and diagrams. Each topic is presented and images in this book are taken from these other texts and MRI
on two pages for easy reference and large subjects have been at a Glance is intended to complement them.
broken down into smaller sections. In the book and compan- Learning MRI physics can be hard work. I hope that this book
ion website I have included simple explanations and animations, helps to demystify it!
vii
Acknowledgements
Once again I thank my friend and colleague John Talbot for Medical Systems and GE for supplying the images, and to all my
his beautiful diagrams and for his support. We make a great friends and family in Brighton, London, Paris, Witney, Leeds, St
team and long may it continue! Thanks again to Philips Augustine, Atlanta and New York.
CW
viii