An increasingly health-conscious population is turning to technology to help in the early detection of disease—mammograms, colonoscopies, and genetic analyses are all becoming more popular. One procedure that might be able to diagnose a variety of health issues is the full-body computed tomographic (CT—often pronounced "cat") scan, which takes a 3-D X-ray image of the body, from the shoulders to the pelvis, in hopes of finding a spot of cancer or the beginning of a clogged artery that a traditional exam might miss. However, while the body is inside the CT scan machine, which looks like a large tube, it is bombarded with radiation. Some scientists from the Columbia University Medical Center looked at how people with similar exposure had been affected.

What they wanted to know: What are the effects of exposure to the radiation levels in a full-body CT scan?

What they did: Because radiation exposure takes decades to develop into malignancies, the scientists looked at a group of people who were exposed to high levels of radiation in the 1940s—Japanese people who were in Hiroshima and Nagasaki when the bombs were dropped. They estimated the dose of radiation to the body from one CT scan, and from an annual CT scan for 30 years and compared it with the dose of radiation people received at different distances from the atomic bombs. They measured the cancer mortality rate of the Japanese people and used it to predict mortality from full-body CT scans.

What they found: The dose of radiation you get from one 20-minute CT scan is the same as if you had been standing a mile and a half away from the atomic bomb blast at Hiroshima, which is "a lot in terms of radiation," said physicist David Brenner, the lead researcher. For a person who is 45 years old when exposed, the risk of cancer is 0.08 percent higher than if not exposed or, put another way, there's a 1 in 1,200 chance (out of all people who have received full-body CT scans) of getting cancer from that procedure. If that same 45-year-old, however, wanted to undergo CT scans every year for the next 30 years, the risk would increase greatly. Then, his chances of getting cancer from the scan are about 1 in 50. The risk from exposure goes down with age, because people are more likely to get diseases from other factors and because radiation-induced cancer takes a long time to develop.

What it means to you: Full-body CT scans have not yet been proven to have any benefit—and radiation exposure isn't the only risk. Full-body scans can find harmful growths but often find harmless scars and bumps, resulting in further tests or even surgery to remove a benign growth. Full-body scans are rarely recommended by physicians, though most will be quick to differentiate full-body from other, localized CT scans, which can be helpful for diagnosing medical problems. You should talk to your doctor before getting any type of CT scan.

Caveats: The study compared the cancer rates of Japanese people living in the 1940s with American people living today, which is a pretty big leap. The authors controlled for some of the variability and noted that the two populations have similar rates of cancer, though the most common types of cancer are different between Japanese and Americans. In addition, the rate of exposure over many years of small doses of radiation may not be the same as the exposure from one large dose, as was the case in Japan.

Find out more: The FDA has come out against full-body CT screenings as a preventative measure. Their reasoning is at: http://www.fda.gov/cdrh/ct/

For an explanation of full-body CT scans, the American College of Radiology and Radiological Society of North America has a website: http://www.radiologyinfo.org/

Read the article: Brenner, D.J. and Elliston, C.D. "Estimated Radiation Risks Potentially Associated With Full-Body CT Screening." Radiology. September 2004, Vol. 232, No. 3, pp. 735-738.

Abstract online: http://radiology.rsnajnls.org