MRI in Practice

Preface to the Fifth Edition ix         

Acknowledgments xi

List of Acronyms xiii

Equation symbols xvii

About the Companion Website xix

Chapter 1 Basic principles  1        

Introduction 1     

Atomic structure 2            

Motion in the atom 2       

MR active nuclei 4             

The hydrogen nucleus 5

Alignment 6

Net magnetic vector (NMV) 8      

Precession and precessional (Larmor) frequency 10

Precessional phase 13        

Resonance 13        

MR signal 18

The free Induction decay(FDI) signal 20

Pulse timing parameters 22

Chapter 2 Image weighting and contrast 24             

Introduction 24

Image contrast  25

Relaxation 25

T1 recovery 26

T2 decay 27

Contrast mechanisms 31   

Relaxation in different tissues 32  

T1 contrast 36       

T2 contrast 40       

Proton density contrast 41

Weighting 42         

Other contrast mechanisms 51

Chapter 3 Spin echo pulse sequences 58  

Introduction 58    

RF rephasing 59

Conventional spin echo 65

Fast or turbo spin echo FSE/TSE) 68

Inversion recovery (IR) 78

Short tau inversion recovery (STIR) 82

Fluid attenuated inversion recovery (FLAIR) 84

Chapter 4 Gradient echo pulse sequences 89

Introduction 89

Variable flip angle 90

Gradient rephasing 91

Weighting in gradient echo pulse sequences 94

Coherent or rewound gradient echo 106

Incoherent or spoiled gradient echo 109  

Reverse-echo gradient echo 113    

Balanced gradient echo 119

Fast gradient echo 122

Echo planar imaging (EPI) 122           

Chapter 5 Spatial encoding 128        

Introduction 128

Mechanism of gradients 129             

Gradient axes 134

Slice-selection 135 

Frequency encoding 142     

Phase encoding 145  

Bringing it all together – pulse sequence timing 152

Chapter 6 k-space 158

Introduction 158     

Part 1 – what is k-space? 159

Part 2 - how are data acquired and how are images created from this data? 165

Part 3 –some important facts about k-space 184

Part 4:: how do pulse sequences fill k-space? 197

Part 5:: options that fill k-space 199

Chapter 7 Protocol optimization 209              

Introduction 209

Signal-to-noise ratio (SNR) 210          

Contrast-to-noise ratio (CNR) 226 

Spatial resolution 232            

Scan time 237         

Trade-offs 238         

Protocol development and modification 238

Chapter 8 Artefacts 242      

Introduction 242

Phase mismapping 243      

Aliasing 253

Chemical shift artefact 261 

Out-of-phase signal cancellation 265

Magnetic susceptibility artefact 269

Truncation artefact 272       

Cross-excitation/cross-talk 273        

Zipper artefact  275

Shading artefact 276             

Moiré artefact 277 

Magic angle 279

Equipment faults 280            

Flow artefacts 280

Flow-dependent (non-contrast enhanced) angiography 298

Black-blood imaging 303

Phase contrast MRA 304

Chapter 9 Instrumentation 311

Introduction 311

Magnetism 313

Scanner configurations 315

Magnet system 318

Magnet shielding 326

Shim system 328

Gradient system 330

RF system 337

Patient transport system 343

Computer system and graphic user interface 344

Chapter 10 MRI safety 346  

Introduction (and disclaimer) 346

Definitions used in MRI safety 347

Psychological effects 350

The spatially-varying static field 351

Electromagnetic (radiofrequency) fields 357

Time-Varying Gradient Magnetic Fields 363

Cryogens 365

Safety tips 367

Additional resources 368

Glossary 370             

Index 387