Americans are exposed to seven times more radiation from diagnostic scans than in 1980, a report found.

Experts said doctors are overusing the tests for profit and raising health risks for patients.

The findings, issued by National Council on Radiation Protection and Measurement, add to already mounting evidence that doctors are ordering too many diagnostic tests, driving up the cost of healthcare in the United States and potentially harming patients.

While diagnostic scans give doctors valuable information and many times are necessary, doctors fear too much radiation exposure can cause cancer, especially in younger people.

"Imaging has literally become the guiding hand of medical practice," said Dr. James Thrall, chair of the American College of Radiology's Board of Chancellors who was not part of the study.

"Unfortunately, one of the things we have seen in the imaging world is that many physicians look at imaging as the solution to their financial problems," Thrall, head of radiology at Massachusetts General Hospital in Boston, said in a telephone interview.

He said imaging technology has created a financial incentive for some doctors to cash in by referring patients to get imaging tests on equipment in their own practices. This is one place the federal government and Congress can look in enacting healthcare reform, Thrall added.

A study by the Government Accountability Office in July found Medicare spending on medical imaging doubled to about $14 billion a year between 2000 and 2006, driven largely by increases in high-tech imaging.

In November, a 10-year study by a team at the University of California, San Francisco, found use of computed tomography or CT scans, an advanced type of X-ray, doubled among patients in a large managed care plan between 1997 and 2006.

Thrall said advanced diagnostic scans have revolutionized the way doctors can treat patients, eliminating the need for unnecessary exploratory surgery and improving patient care.

But hundreds if not thousands of non-radiologists have purchased imaging equipment for their offices, and many studies suggest this has helped to drive up medical costs.

The GAO report, for example, found that from 1998 to 2005, the number of self-referred, in-office CT, MRI and nuclear medicine scans done on Medicare patients grew at triple the rate of the same exams performed in all other settings, such as hospitals or stand-alone imaging centers.

"There is a fundamental problem when the person ordering the study has a direct financial interest in maximizing the use of a particular piece of equipment," Thrall said.

He said the American College of Radiology is working with other radiology groups to craft standards about the appropriate use of imaging, which, when used properly can improve patient care and help cut medical costs.