A published last year in the Archives of Internal Medicine projected that 29,000 future cancers will be directly attributable to the 57 million CT scans performed in the United States in 2007.

Another last year by the National Council on Radiation Protection and Measurements found medical imaging was responsible for about half the total radiation exposure to the typical U.S. resident, up from just 20 percent聽in the 1980s. The council was chartered by Congress to recommend ways to limit radiation exposure.

A 2007 published in The New England Journal of Medicine estimated that 0.4 percent聽of all cancers in the聽country may be attributable to the radiation from CT studies. By adjusting this estimate for current CT use, this estimate might now be as high as 2 percent.

“By definition, an unnecessary exam that uses radiation, such as a CT scan, is an unnecessary exposure to radiation and, in self-referring facilities, perhaps an inordinately high radiation dose since many of them are not properly accredited,” said John Patti, chairman of the American College of Radiology’s board of chancellors.