Safety of Patients and Personnel
ny new method in medicine, be it diagnostic or therapeutic, must be thoroughly checked for possible adverse effects. At the end of the 19th century, x-rays represented a major step forward in medicine, but then sobered physicians and the public after the hazards of ionizing radiation were detected.
No ionizing radiation is involved in MR imaging. However, because of the recognized problems with x-rays and radioisotope examinations, magnetic resonance imaging and spectroscopy have been intensively examined for possible dangerous side effects. During the last 150 years, hundreds of papers focusing on the effects or side effects of magnetic or radiofrequency fields have been published. They range from anecdotal reports about therapeutical applications of magnetic fields as published by Zhang et al. [⇒ Zhang 1984] to reports on unwelcome side effects, such as Beischer’s study [⇒ Beischer 1962].
For a long time, only minimal and reversible physiological effects were reported from imaging and spectroscopy equipment operating below 2 Tesla. Although to date, there is no proof of any permanent damages to patients or staff caused by the magnetic or radiofrequency fields of commonly used clinical MR equipment, for some years negative health effects on humans have been increasingly published – mostly concerning employees working with ultra-high machines between 3 T and 7 T. On the other hand, there are real incidental dangers that can lead to accidents (Figure 18-01 and Figure 18-02).
Magnets can have fatal attractions – whether it is low field or high field.
Left: 900 Gauss (0.09 T) at Paul Lauterbur's first whole-body machine, or right: Decades later at a clinical 1.5 T machine.
This overview cannot cover all potential sources of hazards. Numerous reviews of the literature have been published immediately after the introduction of MR imaging into clinical routine, e.g., by Budinger as early as 1981 [⇒ Budinger 1981], Rinck [⇒ Rinck 1983], by Persson and Ståhlberg [⇒ Persson 1985]; updates are published every so often, for instance in this textbook or, among others, by Budinger [⇒ Budinger 2016].
Several of the side effects associated with MR are unique to this kind of medical diagnostic tool; others are similar to hazards of other diagnostic methods. Possible hazards can arise from or be connected to:
static magnetic fields;
varying magnetic fields (gradient fields);
devices necessary to operate the imaging equipment (such as cooling gases) or to ensure the quality of life of the patients (such as intracorporal implants and extracorporal monitors);
conducting loops such as electrical leads or accidental anatomical positions of the patient.
These hazards can affect patients, personnel, and other persons within the field of the magnet. They can be categorized as incidental and physiological. Nearly all accidents are incidental, caused by negligence (Table 18-01).
The three groups of accidents responsible for more than 90% of all reported injuries to patients and personnel. They are all caused by human negligence – by staff or patient – or the employment of inappropriate or unsuitable equipment or devices [⇒ Rivi FDA].
Table 18-02 lists potential contraindications to MR examinations.