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 ixAcknowledgments xiChapter 1 Systems and safety: MR hardware and fields 1Introduction 1Overview of MRI operation 3MRI hardware 10Electromagnetic fields 16Other medical devices 24Conclusions 25Chapter 2 Let’s get physical: fields and forces 27Basic laws of magnetism 27Magnetic materials 32Forces and torque 39Lorentz and hydrodynamic forces 50Laws of induction 51Conclusions 57Chapter 3 Bio‐effects 1: static field 61Introduction 61Physical mechanisms 61Cellular effects 67Animal effects 69Human physiological effects 70Acute sensory effects 70Epidemiology 70Cognitive effects 74Static field exposure limits 74Conclusions 74Chapter 4 Bio‐effects 2: time‐varying gradient fields 79Introduction 79Physical interaction 79ELF time‐varying magnetic field effects 83Magnetic stimulation 86Peripheral nerve stimulation in MRI 96Exposure limits 99Conclusions 102Chapter 5 Bio‐effects 3: radio‐frequency fields 107Introduction 107Physical interaction 107Tissue heating 112Biological effects 118RF exposure limits 124Controlling SAR in practice 127Conclusions 132Chapter 6 Acoustic noise 137Introduction 137Generation of acoustic noise in MRI 137Measuring noise: dB(A), dB(C), dB(Z) 138Anatomy and physiology of human hearing 143MRI noise exposure 146Reducing acoustic noise in practice 150Hearing protection 151Acoustic noise limits 155Conclusions 158Chapter 7 Pregnancy 161Introduction 161Cellular effects and animal studies 161Human studies and epidemiology 162Gadolinium‐based contrast agents 164Exposure limits and guidance 166Conclusions 169Chapter 8 Contrast agents 173Introduction 173Physical and chemical properties 173Contrast reactions and adverse events 180Pregnancy and lactation 186Conclusions 186Chapter 9 Passive implants 191Introduction 191Risks from passive implants 191ASTM testing 209Examples of passive implants 214Artefacts 218Conclusions 221Chapter 10 Active implants 227Introduction 227Risks from active implants 227Pacemakers and ICDs 236Neurostimulators 243Cochlear implants 249Endoscopic cameras 253Implantable infusion pumps 253Keeping within the conditions 255Conclusions 257Chapter 11 Would you scan this? Understanding the conditions 263Introduction 263MRI conditions 263Understanding fringe field spatial gradient maps 265Understanding RF conditions 275Gradient slew rate condition 278More examples 279Off‐label scanning 281What to do when you do not know the conditions? 281Conclusions 285Chapter 12 Location, location, location: suite design 289Introduction 289ACR zoning scheme 289Fringe field 292Helium exhaust and quench pipe 292Security 296Safety features 297MRI project management 301Specialist systems 302Conclusions 303Chapter 13 But what about us? Occupational exposure 307Introduction 307Occupational exposure limits 307National and international limits 308Surveys of occupational exposure levels 313Survey instrumentation 317Incidence of bio‐effects among magnet facility and MR workers 317Conclusions 317Chapter 14 Organisation and management 321Introduction 321Roles in MR safety 321Policy and safety documentation 324Checklist and screening 326Incidents 328Emergencies 329Training 330Accreditation and certification 331Standards and guidance 333Exposure limits 337Conclusions: the last word 337Appendix 1 One hundred equations you need to know 341Maxwell’s equations 341Magnetic field induction 342Magnetic materials 345Forces and torque 345Forces on moving charges 350Laws of induction 351RF induction from the radiofrequency field 352SAR and tissue heating 354Appendix 2 Maths toolkit 357Coordinate systems 357Vector algebra 358Vector calculus 360Appendix 3 Symbols and constants 363Answers to revision questions 367Index 369