MRI in Practice, 4th Edition

Catherine Westbrook MSc, FHEA, PgC (HE), DCRR,
CTCert, is a Senior Lecturer and postgraduate pathway
leader at The Faculty of Health & Social Care, Anglia
Ruskin University, Cambridge, UK where she is
responsible for the postgraduate course in MRI.
Catherine is also an independent teaching consultant
lecturing on the MRI in Practice Course and other
renowned international courses and conferences. She
is also the author of Handbook of MRI Technique and
MRI at a Glance, also published by Wiley.

Carolyn Kaut Roth RT (R) (MR) (CT) (M) (CV), FSMRT,
is the CEO of Imaging Education Associates, Berwyn,
Pennsylvania, USA delivering a wide variety of learning
resources in MRI and other imaging modalities.

John Talbot MSc, FHEA, PgC (HE), DCRR, is Senior
Lecturer at The Faculty of Health & Social Care,
Anglia Ruskin University, Cambridge, UK where he is
responsible for delivery of undergraduate and postgraduate
modules. John is also an independent teaching
consultant lecturing on the MRI in Practice Course and
developing the companion website animations.

Preface to the Fourth Edition xi

Acknowledgments xiii

Chapter 1 Basic principles 1

Introduction 1

Atomic structure 1

Motion in the atom 2

MR active nuclei 2

The hydrogen nucleus 4

Alignment 4

Precession 8

The Larmor equation 9

Resonance 11

The MR signal 15

The free induction decay signal (FID) 16

Relaxation 16

T1 recovery 16

T2 decay 16

Pulse timing parameters 19

Chapter 2 Image weighting and contrast 21

Introduction 21

Image contrast 21

Contrast mechanisms 22

Relaxation in diff erent tissues 23

T1 contrast 25

T2 contrast 27

Proton density contrast 27

Weighting 29

T2* decay 31

Introduction to pulse sequences 34

Chapter 3 Encoding and image formation 59

Encoding 59

Introduction 59

Gradients 60

Slice selection 62

Frequency encoding 65

Phase encoding 69

Sampling 73

Data collection and image

formation 79

Introduction 79

K space description 80

K space fi lling 81

Fast Fourier transform (FFT) 86

Important facts about K space 90

K space traversal and gradients 96

Options that fill K space 98

Types of acquisition 101

Chapter 4 Parameters and trade-offs 103

Introduction 103

Signal to noise ratio (SNR) 104

Contrast to noise ratio (CNR) 123

Spatial resolution 126

Scan time 131

Trade-offs 134

Decision making 134

Volume imaging 137

Chapter 5 Pulse sequences 140

Introduction 140

Spin echo pulse sequences 141

Conventional spin echo 141

Fast or turbo spin echo 143

Inversion recovery 151

Fast inversion recovery 157

STIR (short tau inversion recovery) 157

FLAIR (fluid attenuated inversion recovery) 159

IR prep sequences 163

Gradient echo pulse sequences 164

Conventional gradient echo 164

The steady state and echo formation 166

Coherent gradient echo 169

Incoherent gradient echo (spoiled) 172

Steady state free precession (SSFP) 175

Balanced gradient echo 179

Fast gradient echo 185

Single shot imaging techniques 186

Parallel imaging techniques 193

Chapter 6 Flow phenomena 198

Introduction 198

The mechanisms of flow 198

Flow phenomena 200

Time of flight phenomenon 200

Entry slice phenomenon 203

Intra-voxel dephasing 206

Flow phenomena compensation 207

Introduction 207

Even echo rephasing 207

Gradient moment rephasing (nulling) 207

Spatial pre-saturation 210

Chapter 7 Artefacts and their compensation 225

Introduction 225

Phase mismapping 225

Aliasing or wrap around 234

Chemical shift artefact 243

Out of phase artefact (chemical misregistration) 244

Truncation artefact 249

Magnetic susceptibility artefact 250

Cross-excitation and cross-talk 252

Zipper artefact 255

Shading artefact 256

Moiré artefact 256

Magic angle 257

Chapter 8 Vascular and cardiac imaging 261

Introduction 261

Conventional MRI vascular imaging techniques 262

Magnetic resonance angiography (MRA) 269

Cardiac MRI 290

Cardiac gating 291

Peripheral gating 298

Pseudo-gating 300

Multiphase cardiac imaging 300

Ciné 301

SPAMM 304

Chapter 9 Instrumentation and equipment 307

Introduction 307

Magnetism 309

Permanent magnets 312

Electromagnets 314

Superconducting electromagnets 317

Fringe fields 321

Shim coils 322

Gradient coils 323

Radio frequency (RF) 330

Patient transportation system 337

MR computer systems and the user interface 337

Chapter 10 MRI safety 341

Introduction 341

Government guidelines 342

Safety terminology 343

Hardware and magnetic field considerations 345

Radio frequency fields 346

Gradient magnetic fields 349

The main magnetic field 351

Projectiles 355

Siting considerations 357

MRI facility zones 358

Safety education 360

Protecting the general public from the fringe field 360

Implants and prostheses 361

Devices and monitors in MRI 367

Pacemakers 367

Patient conditions 368

Safety policy 369

Safety tips 370

Reference 371

Chapter 11 Contrast agents in MRI 372

Introduction 372

Mechanism of action of contrast agents 373

Molecular tumbling 373

Dipole–dipole interactions 375

Magnetic susceptibility 376

Relaxivity 378

Gadolinium safety 380

Other contrast agents 383

Current applications of gadolinium contrast agents 385

Conclusion 393

Chapter 12 Functional imaging techniques 396

Introduction 396

Diff usion weighted imaging (DWI) 397

Perfusion imaging 400

Susceptibility weighting (SWI) 404

Functional imaging (fMRI) 404

Interventional MRI 405

MR spectroscopy (MRS) 407

Whole body imaging 410

MR microscopy (MRM) 411

Glossary 413

Index 427

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