How does MRI work? : an introduction to the physics and function of magnetic resonance imaging,2nd ed.

1 Spin and the Nuclear Magnetic Resonance Phenomenon ....... 1 2 Relaxation ................................................................... 7 2.1 T1: Longitudinal Relaxation ............................................... 7 2.2 T2/T2*: Transverse Relaxation ............................................ 8 3 Image Contrast ............................................................ 11 3.1 Repetition Time (TR) and T1 Weighting ............................... 12 3.2 Echo Time (TE) and T2 Weighting ...................................... 13 3.3 Saturation at Short Repetition Times ................................... 15 3.4 Flip Angle (Tip Angle) .................................................... 17 3.5 Presaturation ................................................................ 18 3.6 Magnetization Transfer .................................................... 19 4 Slice Selection and Spatial Encoding ................................. 21 4.1 Three-Dimensional Spatial Encoding ................................... 26 4.2 K-Space ...................................................................... 27 5 Factors Affecting the Signal-to-Noise Ratio ........................ 29 5.1 Pixel, Voxel, Matrix ........................................................ 30 5.2 Slice Thickness and Receiver Bandwidth ............................... 30 5.3 Field of View and Matrix .................................................. 32 5.4 Number of Excitations ..................................................... 36 5.5 Imaging Parameters ........................................................ 36 5.6 Magnetic Field Strength ................................................... 36 5.7 Coils .......................................................................... 37 5.7.1 Volume Coils ................................................................ 37 5.7.2 Surface Coils ................................................................ 37 5.7.3 Intracavity Coils ............................................................ 37 5.7.4 Phased-Array Coils ........................................................ 38 6 The MR Scanner ........................................................... 41 6.1 The Magnet .................................................................. 42 6.2 The Gradient System ....................................................... 44 6.3 The Radiofrequency System .............................................. 45 6.4 The Computer System ..................................................... 45 VIII 7 Basic Pulse Sequences ................................................... 47 7.1. Spin Echo (SE) Sequences ................................................ 48 7.2 Black Blood Effect .......................................................... 49 7.3 Multislice Imaging ......................................................... 50 7.4 Inversion Recovery (IR) Sequences ...................................... 50 7.5 STIR Sequences ............................................................. 52 7.6 FLAIR Sequences .......................................................... 52 7.7 Gradient Echo (GRE) Sequences ........................................ 52 7.8 Multiecho Sequences ...................................................... 55 8 Fast Pulse Sequences .................................................... 57 8.1 Fast or Turbo Spin Echo Sequences ..................................... 57 8.2 Single-Shot Fast Spin Echo (SSFSE) Sequences ........................ 58 8.3 Fast or Turbo Inversion Recovery (Fast STIR) Sequences ............ 59 8.4 Fast Gradient Echo (GRE) Sequences ................................... 59 8.5 Echo Planar Imaging (EPI) Sequence ................................... 60 8.6 Hybrid Sequences .......................................................... 60 8.7 Gradient and Spin Echo (GRASE) Sequence ........................... 61 8.8 Spiral Sequences ............................................................ 61 8.9 Echo Time and T2 Contrast in Fast Sequences ........................ 62 9 Fat Suppression Techniques ............................................ 63 9.1 Chemical Shift Imaging ................................................... 63 9.2 Frequency-Selective Fat Saturation ...................................... 65 9.3 Short TI Inversion Recovery (STIR) ..................................... 66 9.4 Spectral Presaturation with Inversion Recovery (SPIR) .............. 66 10 Parallel Imaging ........................................................... 69 10.1 Background ................................................................. 69 10.2 Principles of Parallel Imaging ............................................ 69 10.3 Special Requirements ...................................................... 71 10.4 Applications ................................................................. 71 11 Cardiovascular Imaging ................................................. 73 11.1 Angiography ................................................................ 74 11.1.1 Bright Blood Imaging ...................................................... 74 11.1.2 Black Blood Imaging ....................................................... 86 11.1.3 Time-Resolved MR Angiography ........................................ 88 11.2 Perfusion-Weighted Imaging ............................................. 89 11.3 Diffusion-Weighted Imaging ............................................. 91 IX 11.4 The BOLD Effect in Functional Cerebral Imaging .................... 95 11.5 Cardiac Imaging ............................................................ 97 11.6 Cardiac Imaging with SSFP Sequences ................................. 98 11.7 Myocardial Perfusion Imaging ........................................... 99 11.8 Late-Enhancement Imaging ............................................ 101 11.9 Detection of Increased Myocardial Iron Concentrations .......... 102 12 MR Contrast Agents .................................................... 103 12.1 Chemical Structure ...................................................... 107 12.2 Relaxivity .................................................................. 109 12.3 Pharmacologic Properties ............................................... 112 12.3.1 Extracellular Contrast Agents .......................................... 112 12.3.2 Intravascular or Blood Pool Contrast Agents ........................ 115 12.3.3 Liver-Specific Contrast Agents ......................................... 116 12.3.4 RES Contrast Agents ..................................................... 118 12.3.5 Lymph Node-Specific Contrast Agents ............................... 119 12.3.6 Tumor-Targeted Contrast Agents ...................................... 119 12.3.7 Other Emerging Tissue-Specific Contrast Agents ................... 120 12.3.8 Hyperpolarized Gases ................................................... 120 12.3.9 Oral MR Contrast Agents ............................................... 121 12.4 Outlook .................................................................... 122 13 MR Artifacts .............................................................. 129 13.1 Motion and Flow Artifacts (Ghosting) ................................ 129 13.2 Phase Wrapping .......................................................... 131 13.3 Chemical Shift ............................................................ 133 13.4 Magnetic Susceptibility .................................................. 135 13.5 Truncation Artifacts ..................................................... 135 13.6 Magic Angle ............................................................... 136 13.7 Eddy Currents ............................................................ 136 13.8 Partial Volume Artifacts ................................................. 136 13.9 Inhomogeneous Fat Suppression ...................................... 136 13.10 Zipper Artifacts .......................................................... 137 13.11 Crisscross or Herringbone Artifacts ................................... 137 14 High-Field Clinical MR Imaging ...................................... 139 14.1 Tissue Contrast ........................................................... 140 14.2 Magnetic Susceptibility .................................................. 140 14.3 Chemical Shift ............................................................ 140 14.4 Radiofrequency (RF) Absorption ...................................... 141 Contents X 15 Bioeffects and Safety .................................................. 143