Lipton Totally Accessible MRI

A User's Guide to Principles, Technology, and Applications
1. Auflage 2010
ISBN: 978-0-387-48896-7
Verlag: Springer
Format: PDF
Kopierschutz: 1 - PDF Watermark

E-Book, Englisch, 384 Seiten

This practical guide offers an accessible introduction to the principles of MRI physics. Each chapter explains the why and how behind MRI physics. Readers will understand how altering MRI parameters will have many different consequences for image quality and the speed in which images are generated. Practical topics, selected for their value to clinical practice, include progressive changes in key MRI parameters, imaging time, and signal to noise ratio. A wealth of high quality illustrations, complemented by concise text, enables readers to gain a thorough understanding of the subject without requiring prior in-depth knowledge.

Autoren/Hrsg.

Lipton, Michael L.

Inhaltsverzeichnis

1;Dedication Page;5
2;Foreword;6
3;Why This Book?;8
4;A User's Guide;10
5;Acknowledgments;13
6;Table of Contents;15
7;Part I In the Beginning: Generating, Detecting, and Manipulating the MR (NMR) Signal;20
7.1;1 Laying the Foundation: Nuclear Magnetism, Spin, and the NMR Phenomenon;21
7.1.1;The Overall Aim;21
7.1.1.1;Spatial Resolution;21
7.1.1.2;Contrast Resolution;22
7.1.2;Where Does the MRI Signal Come From?;22
7.1.2.1;Nuclear Magnetic Resonance;22
7.1.2.1.1;Spin Semantics;23
7.1.2.1.2;Prerequisites to NMR: Nuclear Magnetism;24
7.1.2.1.3;Prerequisites to NMR: Nuclear Spin Angular Momentum;25
7.1.2.1.4;What Is Spin?;27
7.1.3;Interaction of Protons with a Static Magnetic Field (B);28
7.1.3.1;Describing a Real-Life Sample: Dealing with Many Spins;30
7.1.4;The Energy Configuration Approach: A Painless (Really!) Bit of Quantum Mechanics;30
7.1.4.1;Overview;30
7.1.4.2;Probability and Certainty;31
7.1.4.3;Energy Levels;32
7.1.4.3.1;Minimizing the Energy Configuration;33
7.1.4.4;The Uncertainty Principle;34
7.1.4.5;Summary;34
7.1.4.6;Making the Quantum Mechanical Approach Specific to MRI;34
7.1.5;One More Thing .. . What Exactly Is the MRI Signal That We Measure?;36
7.2;2 Rocking the Boat: Resonance, Excitation, and Relaxation;37
7.2.1;Introduction: How Can We Find a Signal to Measure?;37
7.2.1.1;At Rest, Signal Is Not Detectable;37
7.2.1.2;Net Transverse Magnetization Is Detectable;37
7.2.2;Generating Net Transverse Magnetization;38
7.2.2.1;Resonance;38
7.2.2.2;What Is a Rotating Magnetic Field (Radiofrequency Field)?;39
7.2.2.3;What Happens When the Radiofrequency (BI ) Is Turned On?;41
7.2.2.4;Generating MR Signal;43
7.2.2.5;Points of View: The Laboratory and Rotating Frames of Reference;43
7.3;3 Relaxation: What Happens Next?;45
7.3.1;What Happens When the Radiofrequency Is Shut Off?;45
7.3.2;Separate, but Equal (Sort of): Two Components of Relaxation;45
7.3.2.1;Recovery of Longitudinal Magnetization;46
7.3.2.2;Loss of Transverse Magnetization;46
7.3.2.3;Relaxation Mechanisms;47
7.3.2.3.1;Spin-Lattice (Longitudinal) Relaxation;48
7.3.2.4;The Effects of Variation in B0: T2´;49
7.3.3;The Spin Echo;50
7.3.3.1;A Different Case of the Spin Echo;53
7.3.3.2;The Stimulated Echo;54
7.3.3.2.1;Measuring the MR Signal;55
7.4;4 Image Contrast: Tl, T2, T2*, and Proton Density;56
7.4.1;T2/T2* Contrast;56
7.4.2;T1 Contrast;58
7.4.2.1;Multiple Repetitions Required;58
7.4.2.2;Change the Starting Point;58
7.4.2.3;Contrast Agents and Their Effect on Tl;60
7.4.3;Proton Density Contrast;62
7.4.4;Putting Things Together to Control Image Contrast;63
7.5;5 Hardware, Especially Gradient Magnetic Fields;65
7.5.1;Why This Chapter?;65
7.5.2;The Bo Magnetic Field;65
7.5.2.1;Requirements;65
7.5.2.2;Magnet Designs for Generating Bo;66
7.5.2.2.1;Permanent Magnets and Vertical Fields;67
7.5.2.2.2;Superconducting Magnets and Horizontal Fields;69
7.5.2.2.2.1;Keeping Your Cool: The Cryogen System;70
7.5.2.2.2.2;Losing Your Cool: Magnet Quench;71
7.5.2.3;Shimming;72
7.5.3;Radiofrequency Transmission;73
7.5.3.1;Radiofrequency Calibration;73
7.5.4;The Gradient Magnetic Field;73
7.5.5;The RF Coils;78
7.5.5.1;Tuning;79
7.5.5.2;Impedance Matching;79
7.5.5.3;Surface RF Coils and Coil Sensitivity;80
7.5.5.4;Quadrature RF Coils;80
7.5.5.5;Phased Array Coils;82
7.5.6;The Receiver (A2D);83
7.5.7;The Computer;84
7.5.8;Shielding;86
7.5.8.1;B0 Fringe Field;86
7.5.8.2;Eddy Currents;87
7.5.8.3;RF Shielding;88
7.5.9;The Prescan Process;89
7.5.9.1;Center Frequency Determination;89
7.5.9.2;Receiver Gain Adjustment;90
8;Part II User Friendly: Localizing and Optimizing the MRI Signal for Imaging;91
8.1;6 Spatial Localization: Creating an Image;92
8.1.1;What Is an Image?;92
8.1.1.1;Image Geometry;93
8.1.2;Understanding and Exploiting B0 Homogeneity;94
8.1.2.1;The Gradient Magnetic Field: A Review;94
8.1.2.1.1;Gradient Magnetic Fields Are Linear;94
8.1.2.1.2;Location Is Frequency;95
8.1.2.1.3;A First Look at Signal Localization;95
8.1.3;Slice Selection Using the Gradient Magnetic Field;95
8.1.3.1;Slice Thickness;96
8.1.3.2;Slice Location;98
8.1.3.3;Plane of Section;99
8.1.4;Localizing Signal Within the Plane of the Slice: Background for Frequency and Phase Encoding;99
8.1.4.1;Dividing a Single Signal;99
8.1.4.2;Setting Up for Spatial Localization;100
8.1.4.3;Localization Within the Slice;100
8.1.5;Frequency Encoding: The Next Stage;101
8.1.5.1;Separating Frequencies with the Fourier Transform (Don't Be Afraid!);102
8.1.5.2;Fourier Analysis Applied to the Frequency-Encoded Signal;103
8.1.5.3;How Many Samples Do We Need?;104
8.1.5.4;Frequency Encoding: The Bottom Line;105
8.1.5.5;The One-dimensional Image;106
8.1.6;Phase Encoding and the Two-dimensional Fourier Transform;107
8.1.6.1;How We Don't Do It;107
8.1.6.2;Why Phase Encode?;108
8.1.6.3;How Can Phase Be Detected?;109
8.1.6.4;How "Rapidly" Does Phase Change?;110
8.1.6.5;Filling in the Data;111
8.1.7;Some Comments Regarding k-Space;114
8.1.7.1;What Location in the Image Does a Point ink-Space Represent?;114
8.1.7.2;Topology of k-Space;115
8.2;7 Defining Image Size and Spatial Resolution;118
8.2.1;How Much Area Will Be Included in the Image?;118
8.2.2;Specifying the Field of View;119
8.2.2.1;How Do We Detect Specific Frequencies?;120
8.2.3;Aliasing and Its Fixes;120
8.2.3.1;Sampling Rate, the Nyquist Rule, and Undersampling;120
8.2.3.2;A voiding Aliasing: Oversampling;122
8.2.3.3;How About the Phase-Encoding Direction?;123
8.2.3.4;How Does My MRI Vendor "Stop" Aliasing?;123
8.2.4;Refining the Field of View;124
8.2.4.1;Gradient Strength Determines Field of View;124
8.2.4.2;Sampling Rate Determines Field of View;124
8.2.4.3;Receiver Bandwidth;125
8.2.4.4;Receiver Bandwidth and Field of View;125
8.2.4.5;How Do We Specify Field of View in Real Life?;125
8.2.4.6;How Small Can the Field of View Be?;125
8.2.5;A Footnote Regarding Receiver Bandwidth;126
8.3;8 Putting It All Together: An Introduction to Pulse Sequences;127
8.3.1;Putting It All Together;127
8.3.2;What Exactly Is a Pulse Sequence?;127
8.3.3;The Pulse Sequence Diagram;128
8.3.3.1;It's Just a Timeline;128
8.3.3.2;Notation;128
8.3.4;Building the Pulse Sequence;130
8.3.5;The Spin Echo Pulse Sequence: A First Example;130
8.3.5.1;The Spin Echo Pulse Sequence in a Nutshell;132
8.3.6;What Happens After TE: Multiple Echoes andMultiple Slices;133
8.3.6.1;Multislice Imaging;133
8.3.6.2;Multiecho Imaging;135
8.3.7;The Gradient Echo Pulse Sequence: Gradient Recalled Echo, Fast Field Echo, Fast Low Angle Shot, and So Forth;136
8.3.7.1;What Is a Gradient Echo?;137
8.3.7.2;The Gradient Echo Pulse Sequence in a Nutshell;139
8.3.7.3;What Makes Gradient Recalled Echo Different?;140
8.3.7.4;Partial (AKA Modified) Flip Angles;141
8.3.7.4.1;Introducing Saturation;141
8.3.7.4.2;The Ernst Angle;142
8.3.7.4.3;Controlling T1 Contrast with the Flip Angle;143
8.3.8;Contrast Modification in SE and GRE Imaging;144
8.4;9 Understanding, Assessing, and Maximizing Image Quality;145
8.4.1;What Is the Measure of a Good Image?;145
8.4.2;What Is Noise?;146
8.4.3;Signal-to-Noise Ratio: Measuring Image Quality;146
8.4.4;What Affects Signal to Noise?;148
8.4.5;Contrast-to-Noise Ratio: Measuring Diagnostic Utility;151
8.4.6;Quality Assurance;152
8.4.6.1;The Quality Assurance Measurements;152
8.4.6.1.1;The Quality Assurance Phantom;153
8.4.6.1.2;Signal-to-Noise Ratio;153
8.4.6.1.3;Uniformity;153
8.4.6.1.4;Geometry;154
8.4.6.1.5;Contrast;155
8.4.6.1.6;General Checks;155
8.5;10 Artifacts: When Things Go Wrong, It's Not Necessarily All Bad;156
8.5.1;Things Do Go Wrong ... but It's Not All Bad News;156
8.5.2;Motion;156
8.5.3;Undersampling (Wraparound Artifact);158
8.5.4;Susceptibility Effects: Signal Loss and Geometric Distortion;161
8.5.4.1;Signal Loss;161
8.5.4.2;Geometric Distortion;161
8.5.5;Truncation (Gibbs Artifact);163
8.5.6;Radiofrequency Leak (Zipper Artifact);166
8.5.7;k-Space Corruption: (Corduroy, Herringbone, andSpike Artifacts);167
8.5.8;Chemical Shift Artifact;168
8.5.9;Slice Profile Interactions (Cross-Talk Artifact);170
8.6;11 Safety: First, Do No Harm;171
8.6.1;Who Cares?;171
8.6.2;The Safety of MRI Versus Iatrogenic Injury;171
8.6.3;Types of MRI Risk;172
8.6.3.1;Projectiles;172
8.6.3.2;Bioimplant Malfunction;173
8.6.3.2.1;Risk to the Patient;173
8.6.3.2.2;Risk to the Device;174
8.6.3.3;Burns;174
8.6.3.3.1;Beware Conductive Materials and Loops;174
8.6.3.4;Nerve Stimulation;175
8.6.3.5;Hearing;175
8.6.3.6;Psychological Distress;175
8.6.3.7;Pregnancy;176
8.6.4;Keeping It Safe: S4;176
8.6.4.1;Safety;176
8.6.4.2;Security;177
8.6.4.3;Screening;177
8.6.4.4;Surveillance;177
9;Part III To the Limit: Advanced MRI Applications;180
9.1;12 Preparatory Modules: Saturation Techniques;181
9.1.1;Inversion-Recovery Imaging;181
9.1.2;Spectral Saturation Techniques;185
9.1.2.1;Chemical Shift;185
9.1.2.2;Exploiting Chemical Shift to Saturate Tissue;186
9.1.3;Hybrid Techniques;186
9.1.4;Selective Excitation;186
9.1.5;Spatial Saturation;187
9.1.6;Magnetization Transfer Contrast;188
9.2;13 Readout Modules: Fast Imaging;190
9.2.1;Gradient Echo Approaches: Turbo-Fast Low Angle Shot, Fast Gradient Recalled Echo, Turbo Field Echo;190
9.2.1.1;Residual Transverse Magnetization and Spoiling;191
9.2.2;Steady-State Free Precession: Balanced Turbo Field Echo, True-Fast Imaging with Steady-State Precession, Fast Imaging Employing Steady-State Acquisition;193
9.2.3;Manipulating k-Space: Rapid Acquisition with Relaxation Enhancement, Turbo Spin Echo, Fast Spin Echo;193
9.2.3.1;Fast Spin Echo Contrast;195
9.2.3.2;Extreme Speed: Single-Shot Turbo Spin Echo, Single-Shot Fast Spin Echo, Half Fourier Acquisition Single-Shot Turbo Spin Echo;196
9.2.3.2.1;T1 Contrast in Single-Shot FSE;197
9.2.3.3;Contrast Inversion: MR Hydrography;197
9.2.3.4;Gradient and Spin Echo;198
9.2.4;Hyperspace: Echoplanar Imaging;198
9.2.5;Further Exploits in k-Space;201
9.3;14 Volumetric Imaging: The Three-dimensional Fourier Transform;203
9.3.1;Multislice Versus Volumetric Imaging: Three-dimensional Versus Two-dimensional;203
9.3.2;Two-dimensional Imaging: How Do We Do It?;203
9.3.3;Three-dimensional Imaging: How Do We Do It?;204
9.3.3.1;Slab Selection;204
9.3.3.2;A Variation on Phase Encoding;204
9.3.3.3;The Price: Imaging Time;207
9.3.3.4;The Payoff Spatial Resolution and Signal to Noise;208
9.4;15 Parallel Imaging: Acceleration with SENSE and SMASH;210
9.4.1;Why Another Imaging Technique?;210
9.4.2;So What's New?;210
9.4.3;Basics of Parallel Techniques;211
9.4.3.1;Parallel Radiofrequency Systems;211
9.4.3.2;Coil Sensitivity;211
9.4.3.3;Acquisition Schemes;212
9.4.4;Sensitivity Encoding: SENSE, Integrated Parallel Acquisition Techniques-Modified SENSE (iPAT-mSENSE), Array Spatial Sensitivity Encoding Technique (ASSET);213
9.4.5;Simultaneous Acquisition of Spatial Harmonics: SMASH, Integrated Parallel Acquisition Techniques-Generalized Autocalibrating Partially Parallel Acquisition (iPAT-GRAPPA);214
9.4.6;What Do We Actually Gain and at What Cost?;214
9.4.6.1;Speed;214
9.4.6.2;Susceptibility;215
9.4.6.3;Signal to Noise;215
9.5;16 Flow and Angiography: Artifacts and Imaging of Coherent Motion;216
9.5.1;What Is Magnetic Resonance Angiography Anyway?;216
9.5.2;Basic Principles of Flow for Students of MRI;217
9.5.2.1;Laminar Flow;218
9.5.2.2;Turbulent Flow;218
9.5.3;Impact of Flow on the MR Signal;219
9.5.3.1;High- Velocity Signal Loss;219
9.5.3.2;Dephasing Due to Movement Along a Gradient Magnetic Field;221
9.5.3.3;Phase Misregistration;222
9.5.3.4;Odd Echo Dephasing and Even Echo Rephasing;223
9.5.3.5;Gradient-Moment Nulling (AKA Flow Compensation);224
9.5.3.6;Dephasing Due to Turbulence;226
9.5.3.7;Time-of-Flight Effect;226
9.5.3.7.1;Entry Slice Phenomenon;227
9.5.4;Time-af-Flight MRA;228
9.5.4.1;Maximizing Signal from Flow;228
9.5.4.2;Suppressing Background Signal;229
9.5.4.3;What Type of Contrast Do MRA Images Have Anyway?;230
9.5.4.4;Arteries or Veins;231
9.5.4.5;Two-dimensional or Three-dimensional;232
9.5.4.5.1;What Do We Mean by 2D TOF-MRA?;232
9.5.4.5.2;There Is Another Way: 3D TOF-MRA;232
9.5.4.5.3;Limitations of 3D MRA and Their Solutions;234
9.5.4.5.4;Which Way Do You Go? Two-dimensional Versus Three-dimensional;236
9.5.4.5.5;It Really Is Better if You Go Both Ways: Multiple Overlapping Thin-Slab Acquisition;237
9.5.5;Something Different: Contrast-Enhanced MRA;237
9.5.6;Don't Forget This Pitfall!;241
9.5.7;Phase-Contrast MRA;242
9.5.7.1;The Concept;242
9.5.7.2;Direction Sensitivity in PC-MRA?;243
9.5.7.3;Velocity Encoding and Another Type of Aliasing;244
9.5.7.4;Making the PC-MRA Image;245
9.5.7.5;Direction and Quantification of Flow Derived from PC-MRA Images;246
9.5.8;Where Do We Go from Here?;248
9.6;17 Diffusion: Detection of Microscopic Motion;249
9.6.1;Introduction;249
9.6.2;What Is Diffusion?;249
9.6.3;Effect of Diffusion on the MR Signal;250
9.6.4;Making the MR Image Sensitive to Diffusion;250
9.6.5;What Do Diffusion-Sensitized Images Look Like?;258
9.6.6;Quantitative Diffusion Imaging: The ADC;260
9.6.6.1;The ADC "Map";260
9.6.6.2;Accuracy in Measurement of the ADC;261
9.6.7;Directional Information: DTI;261
9.6.7.1;Real Life: Anisotropy;262
9.6.7.2;Encoding the Direction of Diffusion;262
9.6.7.3;Describing Diffusion Direction: The Diffusion Tensor;262
9.6.7.4;Measuring Anisotropy;263
9.6.7.5;Tractography;265
9.7;18 Understanding and Exploiting Magnetic Susceptibility;267
9.7.1;What Is Magnetic Susceptibility (X) Anyway?;267
9.7.1.1;Effects on Magnetic Field Strength (Bnet);267
9.7.1.2;Where It Really Counts: Effects on Bo HomogeneityWhat if;268
9.7.1.3;Principle Magnetic Susceptibility-Related Effects: Signal Loss and Distortion;269
9.7.2;Proton-Electron Dipole Interactions: The Other Face of Paramagnetism;270
9.7.3;Susceptibility-Related Effects I: Artifacts;270
9.7.4;Susceptibility-Related Effects II: Hemorrhage;271
9.7.4.1;Oxyhemoglobin: The "Hyperacute" Phase;273
9.7.4.2;Deoxyhemoglobin: The "Acute" Phase;273
9.7.4.3;Methemoglobin: The "Subacute" Phase;274
9.7.4.3.1;Location, Location, Location!;274
9.7.4.4;Hemosiderin and Ferritin: The "Chronic" Phase;275
9.7.5;Susceptibility-Related Effects III: Contrast Agents;276
9.7.5.1;Exploiting the PEDI Effect;276
9.7.5.2;Creating Spatial Variability in the Magnetic Field;276
9.7.6;Susceptibility-Related Effects IV: Perfusion Imaging;277
9.7.6.1;Time Series;277
9.7.6.2;Hemodynamic Measures;278
9.7.6.3;Hemodynamic Parameter Images;280
9.7.7;Susceptibility-Related Effects V: Functional MRI;281
9.7.7.1;Physiology offMRI;281
9.7.7.2;The fMRI Acquisition;283
9.7.7.3;fMRI Data Processing;283
9.8;19 Spectroscopy and Spectroscopic Imaging: In Vivo Chemical Assays by Exploiting the Chemical Shift;285
9.8.1;Introduction;285
9.8.2;The Chemical Basis of MRS;285
9.8.3;What Then Is Spectroscopy (MRS) and How Is It Different from MRI?;286
9.8.4;Abundance, Resolution, and Detection;287
9.8.5;The Importance of Field Homogeneity;288
9.8.6;Localization: Single-Voxel Methods;289
9.8.6.1;Stimulated Echo Acquisition Mode;289
9.8.6.2;Point- Resolved Spectroscopy;290
9.8.7;Localization: Chemical Shift Imaging;292
9.8.8;Brain Chemistry: Brief Overview of the Proton Spectrum;294
9.8.8.1;Neuronal Marker: N-Acetylaspartate;294
9.8.8.2;Membrane Marker: Choline;294
9.8.8.3;The Reference Standard: Creatine;295
9.8.8.4;Necrosis: Lactate;296
9.8.8.5;Tissue Loss: Myo-Inositol;296
9.8.8.6;Neurotransmitters: Glutamate;296
10;Appendices;297
10.1;Appendix 1 Understanding and Manipulating Vectors;298
10.1.1;What Are They?;298
10.1.2;What Do We Do with Them?;298
10.2;Appendix 2 Glossary of Terms;300
10.3;Appendix 3 Glossary of Common MRI Acronyms, Abbreviations, and Notations;312
10.4;Appendix 4 Resources for Reference and Further Study;318
11;Index;320