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