To Your Health

Q. I know MRIs are useful in diagnosis, but I'm concerned about the possible side effects. Would a CT scan have fewer side effects?

A. MRI (Magnetic Resonance Imaging) provides an unparalleled view of internal body structures without the use of radiation. It affords a level of detail that is extraordinary compared with any other imaging technique. By "tweaking" the electrical signals generated by the MRI, different tissues in the body can be made to take on different appearances. This can be very helpful to the doctor who reads the MRI in determining if something is normal or not. MRI can be used to make images of every part of the body, including the bones, joints, blood vessels, nerves, muscles, and organs. MRI can even image flowing blood in virtually any part of the body without the injection of a contrast material, which is required in vascular radiology.

Because MRI uses a magnetic field roughly 10,000 times stronger than the natural background magnetism from the earth, it cannot be used in certain circumstances. People with surgical clips, artificial joints, heart pacemakers, IUD contraceptive devices, bullet fragments, or any other metal that cannot be removed should not have MRI scanning because there is a risk that the magnet may cause tissue injury by moving the metal in these areas. Tooth fillings and braces may distort MRI images of the head and neck area, and some people with metal fillings feel a tingling in their teeth during the scan, but this is usually insignificant.

MRI in the first 12 weeks of pregnancy poses a small theoretical risk to the unborn baby, so scans are not often performed on pregnant women. Otherwise, to date there have been no serious side effects documented from MRI except for rare allergic reactions when a contrast agent is used, and Benadryl usually alleviates this problem. The most common MRI contrast agent is gadolinium, a rare earth element that appears to be very safe. Iron-containing contrast agents are used only in special diagnostic procedures.

Unlike Computed Tomographic imaging, there is no radiation involved in MRI. Both can generate three-dimensional pictures of the body, but a CT scan only shows one horizontal slice of the body at a time whereas the MRI image can be viewed from almost every angle. The amount of radiation used during a CT scan is minimal but may cause a very slight increase in the risk of cancer. Supplements of vitamin E, vitamin C, and a host of other antioxidants have been well documented to reduce this risk. Vitamin E specifically protects DNA from radiation damage, but bear in mind that antioxidants work much better as a team, so adding vitamin C, selenium, flavonoids, and perhaps other antioxidants is well worthwhile. In addition, vitamin C plays a key role in the formation of the membrane layer that protects cells.

MRI has the great advantage of being free of radiation. While there is some debate on the details, the risk from radiation used in diagnostic procedures is insignificant compared to risks of doing without the information. We are all exposed to ionizing radiation from natural background sources every day of our lives, and a diet rich in antioxidants is certainly prudent whether or not you have the additional radiation exposure of a diagnostic procedure.