Essentials of MRI Safety

Donald W. McRobbie

• Éditeur: Wiley-Blackwell
• Année: 2020
• ISBN:
  9781119557159
• Édition: 1
• Sujet: Medicine
• Sous-sujet: Medical Technology & Supplies

Essentials of MRI Safety is a comprehensive guide that enables practitioners to recognise and assess safety risks and follow appropriate and effective safety procedures in clinical practice. The text covers all the vital aspects of clinical MRI safety, including the bio-effects of MRI, magnet safety, occupational exposure, scanning passive and active implants, MRI suite design, institutional governance, and more.

Complex equations and models are stripped back to present the foundations of theory and physics necessary to understand each topic, from the basic laws of magnetism to fringe field spatial gradient maps of common MRI scanners. Written by an internationally recognised MRI author, educator, and MRI safety expert, this important textbook:

• Reflects the most current research, guidelines, and MRI safety information
• Explains procedures for scanning pregnant women, managing MRI noise exposure, and handling emergency situations
• Prepares candidates for the American Board of MR Safety exam and other professional certifications
• Aligns with MRI safety roles such as MR Medical Director (MRMD), MR Safety Officer (MRSO) and MR Safety Expert (MRSE)
• Contains numerous illustrations, figures, self-assessment tests, key references, and extensive appendices

Essentials of MRI Safety is an indispensable text for all radiographers and radiologists, as well as physicists, engineers, and researchers with an interest in MRI.

1
Systems and safety: MR hardware and fields

INTRODUCTION

Magnetic resonance imaging (MRI) has grown, from its initial development in the late 1970s to early 1980s, to become one of the most utilized diagnostic imaging modalities. In 2015 there were 103 million MR examinations performed in hospitals from a population of 1.1 billion people in 29 developed countries. A total of 33 000 scanners were in use in 36 countries serving a combined population of 1.7 billion [1].

The two greatest advantages of MRI are its superior soft tissue discrimination compared to X‐rays or CT, and a lack of exposure to ionizing radiation. MRI uses a combination of magnetic fields of varying frequencies: radiofrequency in the megahertz (MHz) region; audio or “very low frequencies” (VLF) up to tens of kilohertz (kHz); and a static field (zero hertz). None of these possesses sufficiently localized concentrations of electromagnetic (EM) energy to damage atoms, molecules, or cells (Figure 1.1). The risk of cancer induction from magnetic field exposures encountered in MRI is quite possibly zero – unlike X‐rays, CT, mammography, or the radioactive tracers used in nuclear medicine. This makes MRI very attractive for serial examinations, for scans of children whose tissues are more sensitive to the ionizing radiation used in alternative modalities, or for research studies on groups of healthy volunteers.

Figure 1.1 The electromagnetic spectrum showing frequency and wavelength of radiations, relative scale, and applications.

So, is MRI safe?

Obviously not, or there would be no need for this book. Whilst later chapters will show that MRI is relatively benign from a biological point of view, the practice of MRI may involve significant risk to the patient and to others present during the examination. The MRI examination room is potentially the most hazardous environment within the radiology department because of the possibility of catastrophic and fatal accidents where practice is poor or where safety protocols are not fully observed or understood.

Nowhere is this better illustrated than in the tragic case of a six‐year old boy who in 2001 was struck by an oxygen tank which had flown into the scanner, later dying from his injuries. This prompted a root and branches review of MR safety practice within the USA by the American College of Radiology [2] leading to a series of recommendations. It is concerning, that even today, not all these recommendations are routinely followed in every institution. In a 10‐year review of MRI‐related incidents reported to the US Food and Drug Administration (FDA) 59% were thermal (excessive heating, burns), 11% mechanical (cuts, fractures, slips, falls, crush and lifting injuries), 9% from projectiles, and 6% acoustic (hearing loss) [3] (Figure 1.2).

Figure 1.2 MRI adverse events reported to the FDA. Data from [3].

A significant source of risk from MRI arises when patients have implants, particularly active implanted medical devices (AIMDs), such as cardiac pacemakers or neuro‐stimulators. However, whereas a decade ago, custom might have been pre‐cautionary – not to scan these patients, modern practice is moving towards finding ways to scan whenever t...