New concerns about excessive doses of radiation from computed tomography (CT) imaging technology have been raised in articles by researchers from Columbia University Medical Center.

Although CT can provide better images than conventional x-rays, its scans expose patients to much higher doses of radiation than do regular x-rays. This means that the 20-fold rise in the numbers of CT scans performed in the U.S. over the past 20 years has markedly increased the radiation exposure of the population. Two of the many uses of CT that have ballooned are for cardiac diagnoses and the evaluation of injuries in emergency departments.

Radiation from a 64-slice CT angiography scan of the heart, for example, exposes an individual to 10 mSv to 15 mSv (millisieverts, a common measure of the effective dose of radiation used in diagnostic procedures), compared with just 0.01 mSv to 0.15 mSV for a standard chest x-ray; 0.005 mSv for a dental x-ray; and the 3 mSv that all of us in the U.S. receive each year from background radiation.

The researchers estimate that about one-third of the 62 million CT scans administered each year in the U.S. (including 4 million in children) are done without "a proven clinical rationale;" that is, they are not medically necessary. Of particular concern is the increasing use of CT as a screening procedure in asymptomatic patients for whom the relative benefit vs. risk evaluation has not been established.

In another study, researchers at Wake Forest University in North Carolina determined the amount of radiation received by 86 consecutive patients at a level-I trauma center within 24 hours of their care. More than half of these people had been in car accidents. The average dose of radiation received by these patients, 40.2 mSv, is approximately equivalent to what a single patient would receive if given 1,000 standard chest x-rays.

Looking at data concerning CT use in the 1990s, the Wake Forest researchers estimated that about 0.4 percent of all cancers in the U.S. at that time could be attributed to radiation from CT. Adjusting this estimate to the much greater numbers of CT currently used, the present estimate of cancer risk due to CT ranges from 1.5 percent to 2.0 percent of all cancers. CT exposure poses an especially great cancer risk for children.

While there may be little you can do to avoid receiving CT scans if you've had an accident, here are several questions you might ask your doctors when they recommend an elective CT:

• Are the results of this CT scan likely to spur changes in my medical care?
• Could another imaging technique, such as a regular x-ray, sonogram, or magnetic resonance test (MRI), be used instead of a CT scan?
• Does this hospital's imaging center have the equipment necessary to carry out a low-dose CT scan?
• Am I likely to need future CT scans as the result of this one?