MRI in Practice

459 Pages·2011·29.2 MB·English

by  Catherine Westbrook

MRI in Practice
Fourth Edition
Catherine Westbrook
MSc, FHEA, PgC(HE), DCRR, CTC
Senior Lecturer
Anglia Ruskin University
Cambridge
UK
Carolyn Kaut Roth
RT (R) (MR) (CT) (M) (CV), FSMRT
CEO, Imaging Educati on Associates
Pennsylvania
USA
John Talbot
MSc, FHEA, PgC(HE), DCRR
Senior Lecturer
Anglia Ruskin University
Cambridge
UK
A John Wiley & Sons, Ltd., Publication
This editi on fi rst published 2011
© 1993, 1998 by Blackwell Science
© 2005, 2011 by Blackwell Publishing Ltd
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First published 1993
Second editi on 1998
Third editi on 2005
Fourth editi on 2011
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Library of Congress Cataloging-in-Publicati on Data
Westbrook, Catherine.
MRI in practi ce / Catherine Westbrook, Carolyn Kaut Roth and John Talbot. – 4th ed.
p. cm.
Includes bibliographical references and index.
ISBN 978-1-4443-3743-3 (pbk. : alk. paper) 1. Magneti c resonance imaging. I. Roth, Carolyn Kaut. II. Talbot,
John, MSc. III. Title.
RC78.7.N83W48 2011
616.07'548–dc22
2010052328
A catalogue record for this book is available from the Briti sh Library.
1 2011
Contents
Foreword ix
Preface to the Fourth Edition xi
Acknowledgments xiii
Chapter 1 Basic principles 1
Introduction 1 Resonance 11
Atomic structure 1 The MR signal 15
Motion in the atom 2 The free induction decay signal (FID) 16
MR active nuclei 2 Relaxation 16
The hydrogen nucleus 4 T1 recovery 16
Alignment 4 T2 decay 16
Precession 8 Pulse timing parameters 19
The Larmor equation 9
Chapter 2 Image weighting and contrast 21
Introduction 21 T2 contrast 27
Image contrast 21 Proton density contrast 27
Contrast mechanisms 22 Weighting 29
Relaxation in diff erent tissues 23 T2* decay 31
T1 contrast 25 Introduction to pulse sequences 34
Contents MRI in Practice
iv
Chapter 3 Encoding and image formation 59
Encoding 59 Introduction 79
Introduction 59 K space description 80
Gradients 60 K space fi lling 81
Slice selection 62 Fast Fourier transform (FFT) 86
Frequency encoding 65 Important facts about K space 90
Phase encoding 69 K space traversal and gradients 96
Sampling 73 Options that fi ll K space 98
Data collection and image Types of acquisition 101
formation 79
Chapter 4 Parameters and trade-off s 103
Introduction 103 Scan time 131
Signal to noise ratio (SNR) 104 Trade-off s 134
Contrast to noise ratio (CNR) 123 Decision making 134
Spatial resolution 126 Volume imaging 137
Chapter 5 Pulse sequences 140
Introduction 140 Conventional gradient echo 164
Spin echo pulse sequences 141 The steady state and echo
formation 166
Conventional spin echo 141
Coherent gradient echo 169
Fast or turbo spin echo 143
Incoherent gradient echo (spoiled) 172
Inversion recovery 151
Steady state free precession (SSFP) 175
Fast inversion recovery 157
Balanced gradient echo 179
STIR (short tau inversion recovery) 157
Fast gradient echo 185
FLAIR (fl uid attenuated inversion
recovery) 159 Single shot imaging techniques 186
IR prep sequences 163 Parallel imaging techniques 193
Gradient echo pulse sequences 164
MRI in Practice Contents
v
Chapter 6 Flow phenomena 198
Introduction 198 Flow phenomena compensation 207
The mechanisms of fl ow 198 Introduction 207
Flow phenomena 200 Even echo rephasing 207
Time of fl ight phenomenon 200 Gradient moment rephasing
(nulling) 207
Entry slice phenomenon 203
Spatial pre-saturation 210
Intra-voxel dephasing 206
Chapter 7 Artefacts and their compensation 225
Introduction 225 Magnetic susceptibility artefact 250
Phase mismapping 225 Cross-excitation and cross-talk 252
Aliasing or wrap around 234 Zipper artefact 255
Chemical shift artefact 243 Shading artefact 256
Out of phase artefact (chemical Moiré artefact 256
misregistration) 244
Magic angle 257
Truncation artefact 249
Chapter 8 Vascular and cardiac imaging 261
Introduction 261 Peripheral gating 298
Conventional MRI vascular Pseudo-gating 300
imaging techniques 262
Multiphase cardiac imaging 300
Magnetic resonance angiography
Ciné 301
(MRA) 269
SPAMM 304
Cardiac MRI 290
Cardiac gating 291
Chapter 9 Instrumentation and equipment 307
Introduction 307 Permanent magnets 312
Magnetism 309 Electromagnets 314
Contents MRI in Practice
vi
Superconducting electromagnets 317 Radio frequency (RF) 330
Fringe fi elds 321 Patient transportation system 337
Shim coils 322 MR computer systems and the
user interface 337
Gradient coils 323
Chapter 10 MRI safety 341
Introduction 341 Safety education 360
Government guidelines 342 Protecting the general public from
the fringe fi eld 360
Safety terminology 343
Implants and prostheses 361
Hardware and magnetic fi eld
considerations 345 Devices and monitors in MRI 367
Radio frequency fi elds 346 Pacemakers 367
Gradient magnetic fi elds 349 Patient conditions 368
The main magnetic fi eld 351 Safety policy 369
Projectiles 355 Safety tips 370
Siting considerations 357 Reference 371
MRI facility zones 358
Chapter 11 Contrast agents in MRI 372
Introduction 372 Relaxivity 378
Mechanism of action of contrast Gadolinium safety 380
agents 373
Other contrast agents 383
Molecular tumbling 373
Current applications of gadolinium
Dipole–dipole interactions 375 contrast agents 385
Magnetic susceptibility 376 Conclusion 393
MRI in Practice Contents
vii
Chapter 12 Functional imaging techniques 396
Introduction 396 Interventional MRI 405
Diff usion weighted imaging (DWI) 397 MR spectroscopy (MRS) 407
Perfusion imaging 400 Whole body imaging 410
Susceptibility weighting (SWI) 404 MR microscopy (MRM) 411
Functional imaging (fMRI) 404
Glossary 413
Index 427
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