Q: Are MRI scanners dangerous?

For the vast majority of people, there is no danger associated with having an MRI scan. For those people whose anatomy contains one or more of the following items, however, it is important to be aware of the possibility that an MRI could cause serious injury or death. Besides complete information about your medical history, your doctor and the MR staff must know if you have any metal in your body which cannot be removed, including:

• pacemakers
• implanted insulin pumps
• aneurysm clips
• vascular coils and filters
• heart valves
• ear implants
• surgical staples and wires
• shrapnel
• bone or joint replacements
• metal plates, rods, pins or screws
• contraceptive diaphragms or coils
• penile implants
• permanent dentures

In the case of metal implants, it is often possible for patients to be scanned without danger. It is very important, however, that you reveal the presence of such items to the radiologist and MRI staff in order for them to evaluate whether or not such danger exists. Also, it is important to tell a member of the staff if you are pregnant or if you believe there is a possibility you are pregnant.

IMPORTANT: DO NOT ALLOW YOURSELF TO BE SCANNED IF YOU HAVE A PACEMAKER OR OTHER IMPLANTED MECHANICALLY, ELECTRICALLY OR MAGNETICALLY ACTIVATED DEVICE. UNLESS SPECIFICALLY ORDERED BY THE RADIOLOGIST, YOU WILL NOT BE SCANNED IF YOU HAVE METAL IMPLANTS IN THE HEAD REGION.

In every MRI scanner, the patient lies in a strong magnetic field. Although the magnetic field is invisible and the patient cannot sense it, the strength of the field can be seen by its effect on a ferromagnetic object. For example, if one holds a metal paper clip in the "fringe" field surrounding an MRI scanner, one can feel the tug of the magnetic field on the paper clip, pulling it toward the center of the magnet. In general terms, it may be said that the stronger the magnetic field, the stronger the pull. The strength of the pull will, however, be affected by the design of the magnet. Most MRI magnets have horizontal fields. These magnets exert a much stronger tug on metal objects located in their fringe fields than scanners with vertical-field magnets, an important safety point you might consider when choosing an MRI scanner. Because metal objects brought inadvertently into the fringe field of a horizontal-field scanner can be propelled with great force into the center of the patient gap in such magnets, the potential for injury from flying objects does exist, although proper precautions make such accidents highly unlikely. Nevertheless, this is one reason-though not the only reason-why FONAR scanners have vertically-oriented magnetic fields.

A metal object brought into the vicinity of a vertical magnetic field will be affected slightly by the field but will not be propelled toward the center of the magnet and thus endanger the patient. Some patients want to know why the scanner is in a special shielded room. This is because the scanner itself needs shielding from outside radio wave interference that can degrade the pictures. The purpose of the shielding is the opposite of what it is for the CAT scanner (an X-ray machine) and other X-ray equipment. In the CAT scanner, its purpose is to shield the outside world from the CAT scanner's X-rays.

close this window