The battery of tests given to a patient having a heart attack in a U.S. hospital adds up to a dose of radiation equivalent to 725 chest X-rays, researchers reported on Monday.

One problem is that each procedure is viewed separately, and a patient's total cumulative dose is not usually considered by doctors ordering the test, the researchers told a meeting of the American Heart Association in Orlando.

On average, a patient admitted to an academic hospital with a heart attack had a cumulative effective radiation dose of 14.5 millisieverts -- about a third the annual maximum accumulation permitted for workers in nuclear power plants.

The average American can expect to receive about 3 millisieverts a year from ground radon or flying in an airplane.

The risk at an individual level is small with one test, but with multiple tests the risk likely increases, said Dr. Prashant Kaul of Duke University Medical Center in Durham, North Carolina, who led the study.

We think physicians should not only have a greater awareness of dose accumulation from the tests they are ordering, but also understand the testing patterns they use for common diagnoses.

About a third of the billions of diagnostic imaging scans done around the world every year involve some aspect of heart disease. The American Heart Association estimates patients' collective doses received annually from radiation-based medical tests jumped 700 percent between 1980 and 2006.

AVERAGE OF SEVEN TESTS

We should not withhold necessary, appropriate tests that involve ionizing radiation. They provide very important information, Kaul said in a statement. We need to be sure they are being done appropriately.

Kaul's team analyzed data from 64,074 patients treated for acute heart attacks between 2006 and July 2009 at 49 academic hospitals.

A patient was given an average of seven tests using ionizing radiation -- the type that can pass through tissues but that also can damage DNA and cells.

Most, or 83 percent of all patients, received chest X-rays. Some 77 percent had catheter procedures such as an angiogram, 15 percent had computed tomography or CT scans and 12 percent had a head CT.

In August a team at Emory University in Atlanta reported in the New England Journal of Medicine that as many as 4 million Americans a year are exposed to high doses of radiation.

And a report in March from the National Council on Radiation Protection and Measurement found Americans are exposed to seven times more radiation from diagnostic scans than in 1980.

Imaging equipment makers such as GE Healthcare, Siemens, Philips and Toshiba Medical Systems are working to develop low-dose CT scanners.

In June U.S. researchers reported in the Journal of the American Medical Association that they had found a way to cut the radiation dose from a heart CT scan by half without sacrificing the quality by tailoring each scan to a patient's weight and heart rate.

Medicine