August 26, 2009 / 9:54 PM / 10 years ago

FACTBOX: Common imaging tests that involve radiation

(Reuters) - A study suggests some younger Americans may be getting too many imaging tests that expose them to worrisome amounts of radiation, which over a lifetime may raise their risk of cancer.

Here are some procedures that deliver the biggest doses of radiation:

* Myocardial perfusion scans, done in patients with heart disease to see how much blood is getting to the heart muscle. For the test, patients are injected with a small amount radioactive liquid. The test on average delivered 15.6 millisieverts of radiation per dose, and accounted for more than 22 percent of the total radiation exposure among people in the study, more than any other test.

For people living in the United States, the normal expected radiation dose from chemicals in the ground or flying in an airplane is 3 millisieverts a year.

Despite its widespread use, there is no evidence that the test saves lives, Dr. Michael Lauer of the National Heart, Lung, and Blood Institute, one of the National Institutes of Health, said in a telephone interview. Lauer, who wrote a commentary in the journal, said one recent trial in diabetics showed the test made no difference in improving patients’ outcome.

* CT scans of the abdomen, pelvis and chest accounted for nearly 38 percent of the total radiation exposure among in the study. CT or computed tomography scans are an advanced type of X-ray. A CT scan of the abdomen delivered 8 millisieverts of radiation, a pelvic CT delivered 6, while a chest CT delivered 7.

Some studies have suggested that some CT scans can deliver as much as 20 millisieverts per dose, depending on the organ and type of study, but they are often much less.

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

* Other common tests that deliver radiation include heart catheterizations done to diagnose clogged heart arteries, which delivered an average effective radiation dose of 7 millisieverts per scan or 4.6 percent of the total radiation dose in the study. That was followed by X-rays to check for lower back problems at 1.5 millisieverts or 3.3 percent of the total, and mammography to check for breast cancer, at 0.4 millisieverts, and accounting for 3.1 percent of the total radiation among study participants.

Reporting by Julie Steenhuysen in Chicago, Editing by Sandra Maler

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