• Chapter 18 • Contents
  Introduction Incidental Hazards  External Objects  MR Equipment  Patient-Related Devices  Other Considerations Physiological Hazards   Static Magnetic Fields  Varying Magnetic Fields  Radiofrequency Fields Regulations and Legal Aspects 

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Chapter Eighteen
Safety of Patients and Staff

18-01 Introduction

t the end of the 19th cen­tu­ry, x-rays represented a major step forward in dia­gnos­tic and therapeutic 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.

Any new method in medicine, be it diagnostic or therapeutic, must be tho­­rou­gh­ly checked for possible adverse effects — and magnets can have fatal at­trac­tions (Figure 18-01).

Figure 18-01:
Magnets can have fatal attractions — whether it is low field or high field.
Top: 900 Gauss (0.09 T) at Paul Lauterbur's first whole-body machine, or …
Bottom: … decades later at a clinical 1.5 T machine.

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 ultrahigh machines between 3 T and 7 T and in­volv­ing both pa­tients and em­ploy­ees.

During the last 150 years, thousands of papers focusing on the effects or side ef­fects of magnetic or radiofrequency fields have been pub­li­shed. They range from anec­do­tal reports about therapeutic 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].

This overview cannot cover all potential sources of hazards. Numerous re­views of the literature have been put forth 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 diagnostic tool; others are si­mi­lar to hazards of other diagnostic methods. These hazards can af­fect patients, personnel, and other persons within the field of the magnet.

They can be categorized as incidental and physiological.

Possible hazards can arise from or be connected to:

static magnetic fields;
varying magnetic fields (gradient fields);
varying magnetic fields (gradient fields);

and specifically:

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.

There is a wide range of incidental dangers that can lead to accidents (Figures 18-01 and 18-02). Three groups of accidents responsible for more than 90% of all re­port­ed injuries to patients and per­­son­nel. Nearly all accidents are incidental, caus­ed by negligence — by staff or patient — or the em­ploy­ment of in­ap­pro­pri­­ate or un­suit­able equipment or devices. The most common hazards of MR imaging are:

Temporary or lasting auditory damage to patients whose ears were not ad­equa­te­ly protected (at high or ultrahigh fields);

second or third degree burns or blisters and skin redness caused by different sources;

injuries caused by ferromagnetic objects ("projectiles") in the magnet room or attached to the patient attracted by the MR equipment.

Figure 18-02:
"Are you wearing any metal?"
Repetitive and de­tailed screening questions prior to an MR imaging examination are the best pre­cau­tion against harm and injuries.

The number of contraindications for MR imaging, functional MR, MR spec­tro­sco­py, and similar techniques has decreased during the last years. In many instances patient-related devices have been adapted for MR imaging purposes. The con­­tra­in­di­ca­tions may change from country to country or at different jurisdictions, but ad­he­ren­ce to them is strongly recommended. Earlier distinction be­tween absolute and relative con­tra­in­di­ca­tions has been replaced by the term "Poten­tial Con­tra­in­di­ca­tions". These include:

Electronically, magnetically, and mechanically activated implants: cardiac pace­makers and implantable cardioverter defibrillators;

lead wires or similar wires;

prosthetic heart valves (in high and ultra-high fields if dehiscence is sus­pect­ed);

other pacemakers, e.g., for the carotid sinus; entricular-peritoneal shunts, coils and stents, insulin pumps, and nerve stimulators;

stapedial and cochlear implants;

hemostatic clips; metallic splinters in the orbit;

makeup, piercings, and tatoos;

in certain cases only: pregnancy, congestive heart failure, and claus­tro­pho­bia.

Details, among them of pregnancy and claustrophobia, are discussed on the fol­low­ing pages.