MRI Physics

ISBN-13: 9781119615026 / Angielski / Miękka / 2021 / 416 str.

Stephen J. Powers

Spis treści

About the Author xvPreface xviiAcknowledgements xixIntroduction 11 Hardware: Magnet Types and Coils 15Magnets 15Coils 172 The Basics 23Why the Hydrogen Molecule? 24The Net Magnetization Vector 26MRI is a Sequence of Events 27Free Induction Decay (FID) 32Relaxation 33Proton Density 38Image Contrast 38The IQ Triangle: Contrast, SNR, Resolution 39B0 and B1 43Free and Bound Protons 443 Image Weighting 47Where Does Image Weighting Come From? 48Time of Repetition (TR) 50Time of Echo (TE) 52TE and TR 54Why Different TR Ranges for Different Field Strengths? 54How Does TR Control T1? 55What Does TR Affect? 56Interpreting the T1 Relaxation Curve 57Time of Repetition: Effects of the TR 57TE: The T1 and T2 of it 58Interpreting the T2 Relaxation Curve 60Effects of TE on Image Contrast 62What Do the Lines on the Curves Really Mean Anyway? 62One Last Weighting Triangle 65T1 and T2 Contrast Review 664 Introduction to the Basic Pulse Sequences 69What is a Pulse Sequence? 69Spin Echo (SE) 70Gradient Echo/Gradient Recalled Echo (GRE) 73Line Diagram Anatomy 74The Ernst Angle 775 Multi Echo Spin Echo Sequence 81Introduction to k-Space 82k-Space: Phase Encoding 85With FSE, Watch the Speed Limit! 86k-Space, ETL, and Image Contrast 87Filling k-Space 89Pros and Cons of FSE 89Another Way to View T2* and 180°s 91Where Do Relaxation and Decay Curves Come From? 92A T2* Curve Compared to the T2 Curve 93Metal Artifact Reduction (MARS) 94Driven Equilibrium: A "Forced T1" 953D FSE: CUBE/SPACE/VISTA 97Single Shot FSE/HASTE 986 Tissue Suppression 105Tissue Saturation versus Suppression 107Inversion Recovery - Part One: STIR 108Inversion Recovery: STIR with Vectors 109Inversion Recovery Part Two: T2 FLAIR 113IR Sequences: T1 and T2 FLAIR 116IR Weightings: STIR, T1 and T2 FLAIR 117Inversion Recovery - Part Two 119The Rupture View 120Tissue Saturation: Chemical Shift 121Chemical Saturation at Low Fields 123Tissue Saturation: SPAIR and SPIR 124The Dixon Technique 126Water Excitation 126Saturation Pulses or Bands 129Subtractions 131Magnetization Transfer 135IR Prepped Sequences 137How is an RF Pulse Selective or Non-Selective? 140Water Excitation Sequences 1427 The Gradient Echo Sequence 145GRE Sequence Structure 147Phase Dispersion and Gradient Reversal 148Analog to Digital Converter (ADC) 149GRE Sequence Image Weighting 149Two Different Kinds of T2 Relaxation 152The GRE Weighting Triangle 153GRE and SE Differences 156Different Gradient Echo Types 157In and Out of Phase TEs 161In Phase/Out of Phase at 1.5 T 1638 Gradient Echo Magnetic Resonance Angiography 167Time of Flight MRA 168TOF Angiography: Two Golden Rules 171Types of MRA Sequences 171TOF Concept in MRA versus MRV 1722D versus 3D 1722D TOF MRAs 1753D TOF MRAs 176In-Plane Saturation 178In-Plane Saturation Avoidance 179Magnetization Transfer (MT) 181Options for Better MRAs 183Phase Contrast MRA 1859 k-Space 191What Is Fourier Transform? 192k-Space Filling 19210 Echo Planar Sequences 203Diffusion Weighted Imaging 205Diffusion Tensor Imaging or White Matter Tractography 215Susceptibility Weighted Imaging 216Brain Perfusion 218Arterial Spin Labeling 222Spectroscopy 22511 Geometric Parameters: Trade-offs and Effects on Image Quality 231Field of View (FOV) Is Your Film Size 232Nex, ACQ, NSA, and SNR 235Scan Matrix 237Frequency Matrix 237Echo Train Length 238Echo Spacing 239Echo Train Balancing 240Slice Thickness and Slice Gap 242Fractional Echo 243Bandwidth 244Rectangular (Rec.) FOV 249No Phase Wrap/Phase Oversampling/Fold-Over Suppression 251Concatenations or Acquisitions 254Sequential Order Acquisition 25512 Image Artifacts 257Motion 258Flow Artifact/Phase Mis-registration 262RF Artifacts 265Wrap/Aliasing/Fold-over Artifact 265Gibbs Artifact (Ringing/Truncation) 268Chemical Shift Artifact 271Cross-talk 276Cross-excitation 278Gradient Warp or Distortion 281Metal Artifacts 281Corduroy Artifact 283Annifact 284Moiré Fringe Artifact or Zebra Artifact 285Magnetic Susceptibility Artifact 286Dielectric Effect or Standing Wave 288Magic Angle Artifact 29013 Gradients 295Physical Gradients 296Logical Gradients 30214 MRI Math 313The Larmor Equation: W0 = gammaB0 314Acquisitions or Nex or NSA 314Scan Time Equations 315Pixel Size and Voxel Volume 317How to Convert Hz per Pixel to MHz 318In and Out of Phase TEs 319Dixon Method or Technique 320SNR and the 3D Sequence 32115 Parallel Imaging 325Parallel Imaging: What Is It? 325When and Where to Use the Speed 326Parallel Imaging: How Does It Work? 327Parallel Imaging: Pros and Cons 33016 IV Gadolinium 335Why We Use Gad 336How Does Gad Shorten the T1 of Tissues? 337The Blood-Brain Barrier 341Post Contrast T2 FLAIR Imaging 342Imaging Gadolinium 345Eovist(r) 347Glossary 351Suggested Reading 388Index 389

O autorze

Stephen J. Powers, BSRT (R), (CT), (MR) is currently an MR Technologist for South Coast Hospital Systems in the USA, and former MRI Clinical Applications Specialist for General Electric Health Care. Stephen has over twenty years of classroom, lecture and clinical instructor experience.