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Hybrid MR-PET Imaging

Hybrid MR-PET Imaging

N Jon Shah

(2018)

Additional Information

Abstract

The combination of two leading imaging techniques – magnetic resonance imaging and positron emission tomography – is poised to have a large impact and has recently been a driver of research and clinical applications. The hybrid instrument is capable of acquiring both datasets simultaneously and this affords a number of advantages ranging from the obvious, two datasets acquired in the time required for one, through to novel applications. This book describes the basics of MRI and PET and then the technical issues and advantages involved in bringing together the two techniques. Novel applications in preclinical settings, human imaging and tracers are described.

The book is for students and scientists entering the field of MR–PET with an MRI background but lacking PET or vice versa. It provides practical details from experts working in the area.


Table of Contents

Section Title Page Action Price
Cover Cover
Hybrid MR-PET Imaging: Systems, Methods and Applications i
Preface vii
Contents xi
Part A - Basics 1
Section I - Magnetic Resonance 1
Chapter 1 - Introduction to Magnetic Resonance Imaging 3
1.1 Introduction 3
1.2 Physics of the Dynamics of Spin 4
1.2.1 Spin 4
1.2.2 Spins in a Magnetic Field 5
1.2.3 Spin Dynamics 7
1.2.3.1 Spin Relaxation 7
1.2.3.2 Bloch Equations: Static Case 8
1.2.3.3 Bloch Equations 8
1.2.3.4 The Rotating Frame of Reference 9
1.2.3.5 Bloch Equations in the Axial Representation 10
1.2.3.6 Bloch Equations: Resonant RF Pulses 11
1.2.3.7 Bloch Equations: Off-resonant RF Pulses 12
1.2.3.8 Bloch Equations: Magnetic Field Gradients 13
1.2.4 Signal Formation 14
1.2.4.1 Free Induction Decay 14
1.2.4.2 Echoes 15
1.2.4.3 Spin Echo 16
1.2.4.4 Gradient Echo 16
1.2.4.5 Stimulated Echo 16
1.2.4.6 The Signal Equation and Demodulation 16
1.3 Imaging 19
1.3.1 Spatial Encoding 19
1.3.1.1 Slice Selection 19
1.3.1.2 Phase Encoding 20
1.3.1.3 Frequency Encoding 22
1.3.1.4 2D vs. 3D Imaging 22
1.3.1.5 The Signal Equation of Spatial Encoding 22
1.3.1.6 Spatial Resolution and Field-of-View 24
1.3.2 Image Reconstruction and Acceleration 24
1.3.2.1 k-Space 24
1.3.2.2 Gibbs Ringing Artefact 25
1.3.2.3 Reconstruction for Non-Cartesian k-Space Trajectories 26
1.4 Magnetic Resonance Pulse Sequences 27
1.4.1 Contrast Generation 28
1.4.2 Slice Selection 28
1.4.3 Frequency Encoding 29
1.4.4 Reconstruction 29
1.4.5 Gradient Echo Sequences 30
1.4.6 Spin Echo Sequences 30
1.4.7 Echo Planar Imaging Sequences 31
1.5 Acceleration in MRI Acquisition 31
1.5.1 Partial Fourier 31
1.5.2 Parallel Imaging 33
1.5.3 Multi-shot, Readout Segmented EPI and EPIK (EPI with Keyhole) 34
1.5.4 Multi-band Imaging 37
1.5.5 Combination of Acceleration Techniques 37
1.5.6 Other Acceleration and Reconstruction Methods 41
References 41
Chapter 2 - MRI Instrumentation 45
2.1 Introduction 45
2.2 Main Magnet 45
2.2.1 Superconducting Magnets 46
2.2.2 Resistive Magnets 49
2.2.3 Permanent Magnets 50
2.2.4 Non-conventional Magnets 50
2.3 Gradient System 51
2.3.1 Gradient Coils 51
2.3.2 Gradient Amplifiers 53
2.3.3 Limiting Effects of Fast Gradients 54
2.4 Shim System 54
2.5 RF System 55
2.5.1 RF Coils 56
2.5.1.1 RX Arrays 56
2.5.1.2 Multi-tuned RF Coils 58
2.5.2 RF Electronics 58
2.5.2.1 Transmit Chain 58
2.5.2.2 Receive Chain 59
2.6 Console/Spectrometer 60
2.7 MRI Suite 60
References 61
Chapter 3 - Selective Applications of MRI for the Brain 64
3.1 Functional MRI (fMRI) 64
3.1.1 Introduction 64
3.1.2 Blood-oxygenation-level-dependent (BOLD) 66
3.1.3 Haemodynamic Response Function (HRF) and fMRI Paradigm 67
3.1.4 Generalised Linear Model (GLM) and Data Analysis 69
3.1.5 An Example Visual fMRI Study 71
3.2 Angiography and Perfusion 72
3.2.1 MR Angiography 72
3.2.1.1 Time-of-Flight (TOF) Method 72
3.2.1.2 Phase-contrast (PC) Method 74
3.2.1.3 CE-MRA 75
3.2.2 MR Perfusion 76
3.2.2.1 DSC-MRI 76
3.2.2.2 DCE-MRI 78
3.2.2.3 Arterial Spin Labelling (ASL) 78
3.3 Diffusion MRI in Brain Tissue 80
3.3.1 Introduction 80
3.3.2 Diffusion Basics and Methods 80
3.3.3 Water Diffusion in Brain Tissue and Diffusion Tensor Imaging 81
3.3.4 Non-Gaussian Diffusion Methods 85
3.3.5 Conclusions 87
3.4 Quantitative Imaging 87
3.4.1 T2 and T2* Mapping 88
3.4.2 T1 Mapping 89
3.4.3 Water Content 90
References 92
Chapter 4 - Ultra-high Field Imaging 101
4.1 Introduction 101
4.2 High-resolution Spectroscopy 102
4.2.1 Properties of Magnetic Resonance Spectroscopy (MRS) 102
4.2.2 Physical Basis of MRS: Chemical Shift and Scalar Coupling 102
4.2.3 Basic Excitation–Acquisition Experiment and Data Processing 103
4.2.4 In vivo Measurements with Spatial Localisation and Water Suppression 106
4.3 X-nuclei 109
4.3.1 Overview 109
4.3.2 X-nuclei Hardware 110
4.3.3 Fast Image Acquisition 110
4.3.4 Multiple Quantum Filtering 111
4.3.5 Expose of Important X-nuclei 112
4.3.5.1 Phosphorus 112
4.3.5.2 Carbon 112
4.3.5.3 Fluorine 112
4.3.5.4 Sodium 113
4.3.5.5 Lithium 114
4.3.5.6 Potassium and Chlorine 114
4.3.5.7 Oxygen 114
4.3.5.8 Deuterium 115
4.4 Anatomical and Functional Imaging 115
4.5 Emerging Applications 117
4.5.1 Phase and Susceptibility Weighted Imaging 117
4.5.2 Quantitative Susceptibility Mapping 118
4.5.3 Chemical Exchange Saturation Transfer (CEST) 119
References 122
Section II - Positron Emission Tomography 129
Chapter 5 - Introduction to PET 131
5.1 Introduction 131
5.2 The Physics of Positron Emitters 132
5.3 The Detector System 134
5.4 Time-of-Flight PET 137
5.5 Depth of Interaction 138
5.6 True, False and Lost Coincidences 138
5.7 Performance Characteristics 140
5.7.1 Spatial Resolution 140
5.7.2 Count Rate Behaviour 141
5.7.3 Sensitivity 142
5.7.4 Accuracy 143
5.7.5 Image Quality 143
5.8 Partial Volume Effect and its Correction 144
5.9 Acquisition Modes 145
References 145
Chapter 6 - Positron Emission Tomography Instrumentation 147
6.1 Basics of Signal Detection in PET 147
6.2 Components 148
6.2.1 Scintillators 148
6.2.2 Photodetectors 149
6.3 PET System Architecture 153
6.3.1 Scintillation Detector 153
6.3.2 PET System Design 157
6.3.3 PET Systems 159
References 161
Chapter 7 - PET Quantification 162
7.1 Tomographic Image Reconstruction 162
7.1.1 Analytical Methods 162
7.1.2 Iterative Methods 165
7.1.2.1 General Recipe 165
7.1.2.2 System Response Matrix 166
7.1.2.3 Example—MLEM 168
7.1.2.4 Maximum A Posteriori (MAP) Reconstruction 170
7.2 Data Corrections 171
7.2.1 Attenuation of Radiation 171
7.2.2 Compton Scattering 173
7.2.3 Detector Normalisation 175
7.2.4 Random Coincidences 176
7.2.5 Detector Deadtime 177
7.2.6 Radioactive Decay 178
7.2.7 Detector Calibration 179
7.3 Patient Motion 179
References 181
Chapter 8 - Kinetic Modelling and Extraction of Metabolic Parameters 183
8.1 Introduction 183
8.2 The Three Components Required for Kinetic Modelling 185
8.3 Kinetic Analysis of a One-tissue Compartment Model 189
8.4 The Kinetic Analysis of a Two- or Three-tissue Compartment Model 192
8.5 Model-based Analysis of Neuroreceptor Metabolism 194
8.6 Parameter Extraction by Linearisation 196
8.7 MR-PET Protocol for Neuroreceptor Studies 199
8.8 Summary 200
References 201
Part B - Hybrid MR-PET Imaging: technical overview 203
Section I - Hardware 203
Chapter 9 - Introduction and Historical Overview 205
9.1 Introduction 205
9.2 Historical Overview 206
References 211
Chapter 10 - MR-PET Instrumentation 214
10.1 Mutual Interferences Between MR and PET 214
10.2 MR Compatible PET Detector Technology 217
10.3 MR-PET System Architecture 219
10.4 Hybrid MR-PET Coils 221
10.5 Mutual Interferences with Other Modalities and Equipment 225
References 227
Section II - Special aspects of Data Corrections in MR-PET 229
Chapter 11 - MR-based Corrections for Quantitative PET Image 231
11.1 Introduction 231
11.2 MR-Based AC 231
11.2.1 The Attenuation Process 232
11.2.2 The Attenuation Correction Process 234
11.2.2.1 Standalone PET Scanners 234
11.2.2.2 PET-CT Scanners 235
11.2.2.3 MR-PET Scanners 236
11.2.2.4 Emission-based Methods 239
11.2.2.5 Final Considerations 239
11.3 Partial Volume Correction 240
11.3.1 Partial Volume Effect (PVE) 240
11.3.2 Partial Volume Correction (PVC) 242
11.3.2.1 Empirical Methods 242
11.3.2.2 Deconvolution Methods 244
11.3.2.3 Anatomically-Guided Methods 245
11.3.2.4 Reconstruction Methods 247
11.3.3 Applications 248
11.4 Image-derived Input Function 248
11.4.1 IDIF in Non-simultaneous MR-PET 249
11.4.2 IDIF in Simultaneous MR-PET 250
11.4.3 Alternative Method 252
11.4.4 Evaluation Methods 252
11.4.4.1 Metrics 252
11.4.4.2 Uncertainties 253
References 253
Chapter 12 - Motion Correction in Brain MR-PET 259
12.1 Introduction 259
12.2 Motion Detection and Tracking 261
12.2.1 External Device-based 261
12.2.2 MR-based 262
12.2.2.1 Navigator-based Motion Information 262
12.2.2.2 Image-based Motion Information 263
12.2.3 PET-based 264
12.2.3.1 Image-based Motion Information 264
12.2.3.2 Raw Data-based Motion Information 265
12.3 Motion Correction Techniques 266
12.3.1 MRI 266
12.3.1.1 Retrospective Motion Correction 266
12.3.1.2 Prospective Motion Correction 268
12.3.2 PET 268
References 270
Section III - Special considerations in MR-PET 273
Chapter 13 - MR-PET Measurement 275
13.1 Introduction 275
13.2 Patient Handling and Measurement Workflows 276
13.2.1 Patient Preparation 276
13.2.2 Image Acquisition and Protocols 277
13.3 Ethical Issues 277
13.3.1 Introduction 277
13.3.2 Risks of Magnetic Fields 278
13.3.3 Radiation Issues 278
13.3.4 Data Protection 279
13.3.5 Incidental Findings 279
13.4 Radiation Protection and Dose Considerations 280
13.5 MR Safety 282
13.5.1 Static Magnetic Field 282
13.5.1.1 Projectile Effect and Magnetic Objects 282
13.5.1.2 Cryogens and Quenching 283
13.5.1.3 Physiological Effects 283
13.5.2 Radiofrequency Fields 284
13.5.2.1 RF Heating and Specific Absorption Rate 284
13.5.3 Gradient Fields 284
13.5.3.1 Peripheral Nerve Stimulation 284
13.5.3.2 Acoustic Noise 285
13.5.3.3 Contraindications and Implanted Medical Devices 285
Acknowledgement 285
References 285
Chapter 14 - Parametric Imaging 288
14.1 Introduction 288
14.2 Parametric Imaging in PET 289
14.2.1 Dynamic PET 289
14.2.2 PET Parameters 290
14.2.3 Challenges 290
14.2.3.1 Reconstruction 290
14.2.3.2 Input Function 291
14.3 Parametric Imaging in MRI 291
14.3.1 Static Parameters 291
14.3.2 Dynamic Parameters 292
14.4 Similarities and Differences in MR-PET Parametric Imaging 294
14.4.1 Spatial Resolution 294
14.4.2 Temporal Resolution 295
14.5 Analysis of Parametric Imaging 295
14.5.1 Region-of-interest and Voxel Comparison 295
14.5.2 Statistical Mapping 296
14.5.3 Connectivity 296
References 297
Chapter 15 - Technical and Methodological Aspects of Whole-body MR-PET 300
15.1 Introduction 300
15.2 MR-PET System Design 301
15.2.1 Dedicated RF Coils 302
15.2.2 PET Bore Design 302
15.3 Software Considerations 303
15.3.1 Attenuation Correction 303
15.3.1.1 Subject Attenuation Correction 303
15.3.1.2 Attenuation Correction of RF Coils 306
15.3.2 Scatter Correction 307
15.3.3 Motion Correction 308
15.3.4 Kinetic Modelling 310
15.4 Discussion 311
15.5 Conclusions 312
Acknowledgement 313
References 313
Part C - Human MR-PET Applications 317
Chapter 16 - Brain 319
16.1 Receptor Binding 319
16.2 Neurodegeneration 324
16.3 Neuro-oncology 326
References 329
Chapter 17 - Clinical Applications of Whole-body MR-PET 333
17.1 General Considerations 333
17.2 Applications in Oncology 335
17.2.1 Prostate Cancer 335
17.2.2 Liver Malignancies 337
17.2.3 Neuroendocrine Tumours 341
17.2.4 Malignancies in Children and Adolescents 342
17.2.5 Other Malignant Tumours 343
17.3 Applications for Benign Diseases 345
17.3.1 Parathyroid Adenoma 345
17.3.2 Imaging of Inflammation 346
17.4 Clinical Applications of Motion Correction 347
Acknowledgements 348
References 348
Part D - Preclinical Applications 351
Chapter 18 - Preclinical Hybrid MR-PET Scanner Hardware 353
18.1 Introduction 353
18.2 Challenges 354
18.2.1 Ultra-high B0 Field Strength 355
18.2.2 Ultra-high Gradient Field Strength 355
18.2.3 RF Interference 356
18.3 Hybrid Preclinical MR-PET Systems 357
18.3.1 Achieved by Modification of PET 357
18.3.1.1 Small Animal Systems Based on Photomultiplier Tubes (PMTs) 357
18.3.1.2 Small Animal Systems Based on Avalanche Photodiodes (APDs) 358
18.3.1.3 Small Animal Systems Based on Silicon Photomultipliers (SiPMs) 359
18.3.2 Achieved by Modification of MRI 362
18.3.2.1 Split Magnet System 362
18.3.2.2 Fast-field Cycling System 363
18.3.3 Achieved Without Modifying Both Systems 363
18.4 Commercially Available Preclinical MR-PET Systems 364
References 365
Chapter 19 - Preclinical Applications of MR-PET 368
19.1 Introduction 368
19.2 Imaging of Tumours 369
19.3 Imaging the Cardiovascular System 371
19.4 Imaging the Central Nervous System (CNS) 372
19.5 Dual-probes in Preclinical MR-PET 373
19.5.1 Sentinel Lymph Node Imaging 374
19.5.2 Conclusions 375
19.5.3 Determination of the Tissue pH 375
19.6 Conclusions 376
References 376
Part E - Tracers 379
Chapter 20 - Radiotracers for PET and MR-PET Imaging 381
20.1 Basic Principle of PET-radiotracer Production 381
20.2 Common PET-radiotracers and Their Applicability Medical Applications 383
20.2.1 [15O]Water 384
20.2.2 [13N]Ammonia 384
20.2.3 l-[S-methyl-11C]methionine 385
20.2.4 2-[18F]Fluoro-2-deoxy-d-glucose 385
20.2.5 O-[18F]Fluoroethyl-l-tyrosine 386
20.2.6 6-[18F]Fluoro-3,4-dihydroxy-l-phenylalanine 387
20.2.7 68Ga-labelled Prostate Specific Membrane Antigen Inhibitors 388
20.3 Bimodal MR-PET Probes 389
20.3.1 Unimodal Approach 390
20.3.2 Bimodal Approach 391
References 394
Subject Index 400