MRI: Basic Principles and Applications

Preface, ix

ABR study guide topics, xi

1 Production of net magnetization 1

1.1 Magnetic fields 1

1.2 Nuclear spin 2

1.3 Nuclear magnetic moments 4

1.4 Larmor precession 4

1.5 Net magnetization 6

1.6 Susceptibility and magnetic materials 8

2 Concepts of magnetic resonance 10

2.1 Radiofrequency excitation 10

2.2 Radiofrequency signal detection 12

2.3 Chemical shift 14

3 Relaxation 17

3.1 T1 relaxation and saturation 17

3.2 T2 relaxation, T2* relaxation, and spin echoes 21

4 Principles of magnetic resonance imaging – 1 26

4.1 Gradient fields 26

4.2 Slice selection 28

4.3 Readout or frequency encoding 30

4.4 Phase encoding 33

4.5 Sequence looping 35

5 Principles of magnetic resonance imaging – 2 39

5.1 Frequency selective excitation 39

5.2 Composite pulses 44

5.3 Raw data and image data matrices 46

5.4 Signal-to-noise ratio and tradeoffs 47

5.5 Raw data and k-space 48

5.6 Reduced k-space techniques 51

5.7 Reordered k-space filling techniques 54

5.8 Other k-space filling techniques 56

5.9 Phased-array coils 58

5.10 Parallel acquisition methods 60

6 Pulse sequences 65

6.1 Spin echo sequences 67

6.2 Gradient echo sequences 70

6.3 Echo planar imaging sequences 75

6.4 Magnetization-prepared sequences 77

7 Measurement parameters and image contrast 86

7.1 Intrinsic parameters 87

7.2 Extrinsic parameters 89

7.3 Parameter tradeoffs 91

8 Signal suppression techniques 94

8.1 Spatial presaturation 94

8.2 Magnetization transfer suppression 96

8.3 Frequency-selective saturation 99

8.4 Nonsaturation methods 101

9 Artifacts 103

9.1 Motion artifacts 103

9.2 Sequence/Protocol-related artifacts 105

9.3 External artifacts 119

10 Motion artifact reduction techniques 126

10.1 Acquisition parameter modification 126

10.2 Triggering/Gating 127

10.3 Flow compensation 132

10.4 Radial-based motion compensation 134

11 Magnetic resonance angiography 135

11.1 Time-of-flight MRA 137

11.2 Phase contrast MRA 141

11.3 Maximum intensity projection 144

12 Advanced imaging applications 147

12.1 Diffusion 147

12.2 Perfusion 153

12.3 Functional brain imaging 156

12.4 Ultra-high field imaging 158

12.5 Noble gas imaging 159

13 Magnetic resonance spectroscopy 162

13.1 Additional concepts 162

13.2 Localization techniques 167

13.3 Spectral analysis and postprocessing 169

13.4 Ultra-high field spectroscopy 173

14 Instrumentation 177

14.1 Computer systems 177

14.2 Magnet system 180

14.3 Gradient system 182

14.4 Radiofrequency system 184

14.5 Data acquisition system 186

14.6 Summary of system components 187

15 Contrast agents 189

15.1 Intravenous agents 190

15.2 Oral agents 195

16 Safety 196

16.1 Base magnetic field 197

16.2 Cryogens 197

16.3 Gradients 198

16.4 RF power deposition 198

16.5 Contrast media 199

17 Clinical applications 200

17.1 General principles of clinical MR imaging 200

17.2 Examination design considerations 202

17.3 Protocol considerations for anatomical regions 203

17.4 Recommendations for specific sequences and clinical situations 218

References and suggested readings 222

Index 225