Heart CT Means High Radiation Exposure

Feb. 4, 2009— -- A test commonly ordered by cardiologists across the country to diagnose heart disease exposes patients to radiation doses equivalent to 600 chest X-rays, researchers have found.

The test is called a cardiac CT angiogram, or cardiac CTA for short, and it is a relatively new way to look for potentially dangerous blockages in the heart arteries.

The study, released Tuesday in the Journal of the American Medical Association, is the first to look at radiation exposure from this test, and it is important because of the risk for developing cancer from radiation exposure.

"The strength of [this study] is that it is the first available survey of radiation doses in cardiac CTA," said Dr. Thomas Gerber, study author and associate professor of medicine and radiology at the Mayo Clinic in Rochester, Minn. "That information wasn't known, but it is conceivably important because of the risks of ... radiation."

However, the authors and experts in the field caution that this study should not send patients and doctors fleeing from an important way to diagnose heart disease.

"Not all cardiac CT is evil," said Gerber. "It is valuable in patients who have symptoms of heart disease."

The risk of dying from cancer because of the radiation exposure from one cardiac CTA is difficult to estimate, but the American Heart Association puts the additional risk at around 0.05 percent in a statement released in the journal Circulation.

The actual radiation dose here may also not be as big as it initially sounds.

Radiation is commonly measured in units called millisieverts, or mSv. Authors studied almost 2,000 patients who had a cardiac CTA, and they found that the average radiation dose from these CT scans was 12 mSv.

Gerber said, "This is four times the annual background radiation [that everyone gets] from substances [in the environment] such as radon."

So in other words, an encounter with a heart CT scan equals four years worth of the radiation one would encounter in their day-to-day lives.