Looking at and reading about the incidents during MR examinations last year, one gets the impression that the safety of patients and personnel seems to have become a neglected topic, and accidents appear to be increasing because there is a lack of information and training. The recent accidents in Sweden, for example, have clearly been provoked by thoughtlessness -- they simply seem to be self-inflicted.
MR machines are not toys, and operating them requires concentration as well as knowing and not forgetting the rules. There is also a lack of hierarchy and strictness of the superiors as there is a lack of due diligence, dutifulness, and sense of responsibility by healthcare managers and administrators. In any police inquiry in Sweden, these bureaucrats should be included too.
During the past 150 years, thousands of papers focusing on the effects or side effects of magnetic or radiofrequency fields have been published. They can be categorized as incidental and physiological. There is a wide range of incidental dangers that can lead to accidents. They are all caused by human negligence -- mostly by staff, occasionally by patients -- or the employment of inappropriate or unsuitable equipment or devices.
What are the dangers?
Incidental hazards are created by the static magnetic field usually covering an ellipsoid region around the isocenter of the MRI machine. The range of this fringe or stray field depends on the field strength of the system, the type of magnet, and the kind of shielding used. The fringe field around the MRI system may stretch into adjacent rooms, floors, and even gardens and parking places outside the building. It both influences electronic equipment and can be a possible hazard to persons passing by.
Danger and prohibition symbols and signs used worldwide at MR installations.Appropriate warning signs must be posted. In this case, warning signs or similar notices should be displayed outside the magnet room, in neighboring rooms on the same floor, and on floors above and below. Shielded magnets have reduced this danger.
Ultralow and low-field magnets possess a limited stray field of sometimes less than a 1 m radius from the isocenter of the magnet. The stray field of large-bore, high-field systems may cover a radius of 15 m or 20 m, unless the magnet is heavily shielded.
Three groups of accidents are responsible for more than 90% of all reported injuries to patients and personnel. The most common hazards are temporary or lasting auditory damage to patients whose ears were not adequately protected, usually at 1.5 tesla or 3 and 7 tesla. Other hazards are second- or third-degree burns or blisters and skin redness caused by, for instance, electrocardiogram leads or similar sources.
The most publicly discussed injuries are created by ferromagnetic objects ("projectiles") attracted by the magnet that are attached to the patient or to people entering the magnet room, as happened in the Swedish Lapland incident.
Constant education and obligatory safety drills for everybody involved in MRI are vital. Every person working in or entering the magnet room or adjacent rooms with a magnetic field has to be instructed about the dangers. This should include intensive care staff and maintenance, service, and cleaning personnel, as well as the crew at the local fire station.
The best protection against this danger is not to allow personnel other than those directly involved in patient examinations -- i.e., the operator and the radiologist -- into the magnet room by building the room with a closed and controlled access. As a general rule, access to the magnet room should be limited to trained and responsible personnel or to thoroughly screened patients and visitors who are accompanied by trained personnel.
To date there is no proof of any permanent damage to patients or staff caused by the magnetic or radiofrequency fields of commonly used clinical MRI equipment; however, for some years, information about negative health effects on humans has been increasingly published -- mostly concerning 3- to 7-tesla machines and involving both patients and employees.
Considering the importance of MRI safety, the European Magnetic Resonance Forum and the Round Table Foundation offer a free personal offprint of the chapter on safety from the 12th edition of the textbook Magnetic Resonance in Medicine: A Critical Introduction. The figure in this column comes from this chapter.
Dr. Peter Rinck, PhD, is a professor of radiology and magnetic resonance and has a doctorate in medical history. He is the president of the Council of the Round Table Foundation (TRTF) and the chairman of the board of the Pro Academia Prize.
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