According to a new study people who undergo the heart test computed tomography (CT) scans can be exposed to a dramatic range of radiation. The study published in the Journal of the American Medical Association follows on the heels of a recommendation in an advisory by the American Heart Association published in Circulation to say CT scans should be used judiciously in order to minimize exposure to ionizing radiation.

"It is a coincidence," said Dr. Thomas C. Gerber, an associate professor of medicine and radiology at the Mayo Clinic in Jacksonville, Fla. "These projects have been going on for months or years. The timing ultimately was a coincidence." Gerber was an author of the study and lead author of the advisory.

The study focused on 1965 patients who were undergoing 64 slice cardiac CT scans, also known as cardiac CT angiography at 50 medical centers in various countries including the United States. The researchers found the radiation varied more than six fold and ranged from 331 mGy x cm (a measure of absorbed radiation) to 2,146 mGy cm. The median of exposure was roughly equivalent to
600 chest X-rays, or about 12 milliSievert (mSv) of radiation.

Jorg Hausleiter, M. D., of the University of Munich in Germany and the study author of the JAMA study said the traditional angiography involves a catheter inserted through a blood vessel and dye is injected near the heart. This procedure is said to expose patients to roughly half the dose that a CT angiography does and about the same as other standard cardiac screenings such as the nuclear stress tests do.

There were variations in the exposure depending on the medical center as well as the way the tests were performed. Approximately 80 % of the centers used radiation reducing techniques such as adjusting the CT scan to the size of the patient wherein the smaller the patient the less the radiation, or by precisely timing the radiation dose to a particular point in the heart rhythm and thereby shortening the duration of the exposure.

Surprisingly the wide range of exposure seen in the study was not due to the technician's incompetence. Gerber said, "We actually thought it would be wider. It has nothing to do with technician competence. It's that there is not one protocol of radiation setting that applies to all patients."

There are numerous factors that affect the amount of radiation and one of them is what is being scanned, Gerber said all or part of the heart. Other factors are the heart rate of the person being scanned, the regularity of the heart rate and other factors.

Dr. Andrew J. Einstein, an assistant professor of clinical medicine in radiology at Columbia University said, "Some sites are more concerned and more careful about radiation exposure, and attention must be paid to reducing the radiation dose."

A lower-radiation technique called sequential scanning has being introduced which can reduce radiation exposure by 78 % and is being widely adopted, Einstein said.

According to Hausleiter, overall the danger posed by radiation is very small and he said being exposed to 10 mSv increases an individual's cancer risk by 0.02 percent, however, the greater the exposure to radiation, the greater the risk.

Both Einstein and Hausleiter said that when cardiac CT angiography is used appropriately for people with chest pain suggesting blocked heart arteries, rather than just as a screening test for people with no symptoms of heart disease, the benefits far outweigh the risk of the radiation.

Gerber said. "CT angiography tends to be very valuable for patients who have symptoms or are at high risk for coronary artery disease." Einstein said, "We don't think it should be used for screening purposes."

Both Einstein and Gerber said studies to evaluate the risk benefit balance of CT scans are needed. "Most of us understand that the benefits have never been demonstrated in such a study," Einstein said. "There are a number of proposals that have been submitted to the National Institutes of Health for such studies."