ROCKVILLE, Md. (Reuters Health) - Regulators at the Food and Drug Administration (news - web sites) (FDA) are concerned that the growing popularity of high-tech computerized body imaging for health screening could be exposing the public to risky levels of radiation, according to agency officials.

 Recent advances in computerized tomography (CT) technology have increased the efficiency and lowered the price of the scans. The changes have helped spawn a new nationwide industry of unregulated boutique clinics where patients pay $300 to $500 of their own money to get CT scans not for diagnosis, but for regular health screening, officials told an FDA advisory panel Thursday.

 The agency is worried that easily available screening with CT has the potential of exposing patients to unhealthy repeat doses of the X-ray radiation the machines use to form images. While FDA evaluates the safety and effectiveness of CT scanners and other medical devices for regular use, it has no power to regulate how those machines are used once they reach doctors offices.

 ``We don't have dose limits on CT. How the operator uses it is totally out of our control,'' Dr. Thomas B. Shope, a special assistant at FDA's Center for Devices and Radiological Health (CDRH), said in an interview with Reuters Health.

 Shope and others stressed that improvements in CT screening have increased the efficiency and quality of the scans, greatly enhancing doctors' ability to diagnose diseases inside the body. CT machines can now cheaply and quickly scan patients' whole bodies instead of just small areas of tissue.

 Whole-body scans require higher doses of the X-ray radiation CT scanners use to make images. As more and more people visit clinics to be screened for lung cancer, heart disease and other ailments, they could be absorbing more radiation more often than the FDA originally intended.

 ``It's an open free-for-all in many communities,'' said Dr. John F. Cardella, a member of the advisory panel and the chief of the radiology department at the State University of New York Upstate Medical University in Syracuse. ``There is a perception by the public that CT scanning is a benign thing,'' he said.

 Shope told the panel that the average whole-body CT scan delivers 0.2 to 2..0 rads of radiation, depending on the size of the patient's body. Studies of Japanese survivors of the US atomic attacks on Hiroshima and Nagasaki in WWII linked an increased risk of cancer to lifetime cumulative exposures of 5 to 20 rads.

 ``At 2 rads per exam, we're not far'' from potentially dangerous radiation doses, he said.

 Most doctors who work with CT scanners know to monitor the cumulative radiation doses patients receive. Professional societies also put out guidelines designed to promote the safe and effective use of the machines. But the self-pay nature of many CT boutiques allows patients to visit several different clinics as often as they like.

 No one knows exactly how many radiology clinics offer CT scans for health screening or exactly how well they track radiation doses delivered to patients. A recent FDA survey of 157 clinics showed that 43% use established techniques designed to minimize radiation doses child patients receive.

 ``There is a long way to go in getting all facilities to use appropriate techniques with pediatric patients,'' said Dr. Stanley H. Stern, a CDRH official.

 Shope said that there is growing interest within FDA and the CT industry around technology that allows machines to automatically adjust the X-ray dose depending on how much radiation the body is absorbing during a scan. Such advances might help physicians minimize the potential danger of repeat CT scans in an uncontrolled environment.

 ``We don't really have a feel for just how many boutique clinics are operating. It's something we need to have an awareness of,'' Shope said.