Essentials of MRI Safety

DONALD W. MCROBBIE has more than thirty years' experience in MRI safety. He is currently Adjunct Associate Professor, Discipline of Medical Physics in the School of Physical Sciences at the University of Adelaide, Adelaide, Australia.

Foreword ix Acknowledgments xi Chapter 1 Systems and safety: MR hardware and fields 1 Introduction 1 Overview of MRI operation 3 MRI hardware 10 Electromagnetic fields 16 Other medical devices 24 Conclusions 25 Chapter 2 Lets get physical: fields and forces 27 Basic laws of magnetism 27 Magnetic materials 32 Forces and torque 39 Lorentz and hydrodynamic forces 50 Laws of induction 51 Conclusions 57 Chapter 3 Bioeffects 1: static field 61 Introduction 61 Physical mechanisms 61 Cellular effects 67 Animal effects 69 Human physiological effects 70 Acute sensory effects 70 Epidemiology 70 Cognitive effects 74 Static field exposure limits 74 Conclusions 74 Chapter 4 Bioeffects 2: timevarying gradient fields 79 Introduction 79 Physical interaction 79 ELF timevarying magnetic field effects 83 Magnetic stimulation 86 Peripheral nerve stimulation in MRI 96 Exposure limits 99 Conclusions 102 Chapter 5 Bioeffects 3: radiofrequency fields 107 Introduction 107 Physical interaction 107 Tissue heating 112 Biological effects 118 RF exposure limits 124 Controlling SAR in practice 127 Conclusions 132 Chapter 6 Acoustic noise 137 Introduction 137 Generation of acoustic noise in MRI 137 Measuring noise: dB(A), dB(C), dB(Z) 138 Anatomy and physiology of human hearing 143 MRI noise exposure 146 Reducing acoustic noise in practice 150 Hearing protection 151 Acoustic noise limits 155 Conclusions 158 Chapter 7 Pregnancy 161 Introduction 161 Cellular effects and animal studies 161 Human studies and epidemiology 162 Gadoliniumbased contrast agents 164 Exposure limits and guidance 166 Conclusions 169 Chapter 8 Contrast agents 173 Introduction 173 Physical and chemical properties 173 Contrast reactions and adverse events 180 Pregnancy and lactation 186 Conclusions 186 Chapter 9 Passive implants 191 Introduction 191 Risks from passive implants 191 ASTM testing 209 Examples of passive implants 214 Artefacts 218 Conclusions 221 Chapter 10 Active implants 227 Introduction 227 Risks from active implants 227 Pacemakers and ICDs 236 Neurostimulators 243 Cochlear implants 249 Endoscopic cameras 253 Implantable infusion pumps 253 Keeping within the conditions 255 Conclusions 257 Chapter 11 Would you scan this? Understanding the conditions 263 Introduction 263 MRI conditions 263 Understanding fringe field spatial gradient maps 265 Understanding RF conditions 275 Gradient slew rate condition 278 More examples 279 Offlabel scanning 281 What to do when you do not know the conditions? 281 Conclusions 285 Chapter 12 Location, location, location: suite design 289 Introduction 289 ACR zoning scheme 289 Fringe field 292 Helium exhaust and quench pipe 292 Security 296 Safety features 297 MRI project management 301 Specialist systems 302 Conclusions 303 Chapter 13 But what about us? Occupational exposure 307 Introduction 307 Occupational exposure limits 307 National and international limits 308 Surveys of occupational exposure levels 313 Survey instrumentation 317 Incidence of bioeffects among magnet facility and MR workers 317 Conclusions 317 Chapter 14 Organisation and management 321 Introduction 321 Roles in MR safety 321 Policy and safety documentation 324 Checklist and screening 326 Incidents 328 Emergencies 329 Training 330 Accreditation and certification 331 Standards and guidance 333 Exposure limits 337 Conclusions: the last word 337 Appendix 1 One hundred equations you need to know 341 Maxwells equations 341 Magnetic field induction 342 Magnetic materials 345 Forces and torque 345 Forces on moving charges 350 Laws of induction 351 RF induction from the radiofrequency field 352 SAR and tissue heating 354 Appendix 2 Maths toolkit 357 Coordinate systems 357 Vector algebra 35