MRI Safety

Prior to allowing a patient or support staff member into the scan room, he or she is thoroughly screened for metal objects. Up to this point, we have only talked about external objects. Often however, patients have implants inside them that make it very dangerous for them to be in the presence of a strong magnetic field. Metallic fragments in the eye are very dangerous because moving those fragments could cause eye damage or blindness. Your eyes do not form scar tissue as the rest of your body does. A fragment of metal in your eye that has been there for 25 years is just as dangerous today as it was then -- there is no scar tissue to hold it in place. People with pacemakers cannot be scanned or even go near the scanner because the magnet can cause the pacemaker to malfunction. Aneurysm clips in the brain can be very dangerous as the magnet can move them, causing them to tear the very artery they were placed on to repair. Some dental implants are magnetic. Most orthopedic implants, even though they may be ferromagnetic, are fine because they are firmly embedded in bone. Even metal staples in most parts of the body are fine -- once they have been in a patient for a few weeks (usually six weeks), enough scar tissue has formed to hold them in place. Each time we encounter patients with an implant or metallic object inside their body, we investigate thoroughly to make sure it is safe to scan them. Some patients are turned away because it is too dangerous. When this happens, there is usually an alternative method of imaging that can help them.

Photo courtesy NASA This image set is comparing a young individual (left) with an athletic male in his 80's (center) and with a person of similar age having Alzheimer's Disease (right), all imaged at the same level.

There are no known biological hazards to humans from being exposed to magnetic fields of the strength used in medical imaging today. Most facilities prefer not to image pregnant women. This is due to the fact that there has not been much research done in the area of biological effects on a developing fetus. The first trimester in a pregnancy is the most critical because that is the time of the most rapid cellular reproduction and division. The decision of whether or not to scan a pregnant patient is made on a case-by-case basis with consultation between the MRI radiologist and the patient's obstetrician. The benefit of performing the scan must outweigh the risk, however small, to the fetus and mother. Pregnant MRI technologists can still work in the department. In most cases, they are simply kept out of the actual scan room during their pregnancy.