"Why wait for symptoms to occur?" The radio ad is pitching the latest example of how entrepreneurial America's medical care system has become.

Whole-body scans are now advertised to healthy people along with the idea that finding disease early can be nothing but beneficial.

The use of scanners to screen people for heart disease and cancer before the appearance of symptoms is relatively new. Until the last few years, such expensive, high-tech equipment was reserved solely for diagnosis-as the last-resort, state-of-the-art method for diagnosing people whose symptoms require further investigation. This has begun to change dramatically with a trend that started on the West Coast. Centers with names like AmeriScan and Imaging for Life have opened in large cities. Their popularity got a major boost when Oprah Winfrey enthusiastically described her own whole-body scan experience on national TV last year.

Billed as a "high-tech medical check-up," the scans are costly, ranging from about $300 for a lung scan to $1,000 for the whole body. People typically go for scanning without a doctor's recommendation; and they usually pay out of pocket, as most insurance companies do not cover these tests. And rightly so. The use of scanners as screening tests is a bad idea for two reasons: false alarms and too much radiation. This article will explore radiation risk only because many past issues of Dr. M's Senior Health Tips have addressed other harms caused by screening, including unnecessary biopsies, unnecessary cancer treatment, and false reassurance. Many organs of the body, most notably, the breast and prostate, harbor small cancers that would safely remained dormant had they never been discovered and surgically removed. Similar concerns about overtreatment apply to finding blockages in the coronary arteries of symptomless people.

CT scans involve much higher doses of radiation than standard x-rays because they provide three-dimensional, multiple "slices" of the body. A CT chest scan, for example, involves about 400 times the radiation dose of a single chest x-ray. A CT scan of the abdomen or pelvis involves a radiation dose 500 times that of a chest x-ray. The 2000 European Commission Directorate-General for the Environment reported these dose estimates based on surveys of diagnostic medical tests conducted at hundreds of hospitals in the 1990s.

There is no equivalent U.S. agency that provides similar effective-dose guidelines for tests involving radiation exposure. Nor do we have an independent agency that regulates the use of CT scanners. The consumer is left with the radiologist's word regarding low-dose equipment claims. There is no inspection of these scanning centers as there is for mammography facilities, which are regulated by the Food and Drug Administration. The FDA sends warning letters to the mammography facilities whose equipment is found to emit higher than necessary radiation and shuts down any facility whose equipment is known to emit excessively high radiation.

All x-ray and scanning facilities should get this kind of oversight, but they don't. The FDA is currently considering the issue of regulation, according to Thomas B. Shope, Jr., PhD, of the FDA's Center for Devices and Radiological Health. In a telephone interview, Dr. Shope said that radiologists at these new scanning centers are, in effect, selling a service that is "off label," which means that CT scans are intended for diagnostic purposes but not for screening symptomless people. Furthermore, there is no requirement for the manufacturers to prove their equipment is safe and effective for this new use. All scanners are "grandfathered" because the original CT scanning equipment came on the market before 1976, when the FDA first began requiring proof of safety and efficacy for medical devices.

As a result, the new scanners with their purported improvements of high resolution and low-dosage are merely cleared by the FDA, as opposed to approved. The latter entails a more rigorous review to prove safety and efficacy, which is similar to that required of a new drug or medical device.

To receive FDA clearance, Dr. Shope explained, the equipment manufacturers merely had to show that their machines are equivalent to the older CT scanner in dose and image quality.

Much more rigorous FDA oversight is long overdue. Last year, a small survey of hospitals in the Midwest showed that children undergoing CT scans were exposed to adult doses of radiation that were higher than necessary to produce good image quality.

The scanning centers are allowed to get away with misleading advertising. As things stand now, the FDA cannot challenge even the most obvious erroneous claim, unless the equipment brand and model number is identified in the ad. All a scanning center has to do is avoid mention of this information, and they are free to mislead us all they want.