The most serious problem with the widespread use of CAT scans is the radiation these devices leave in our bodies. CAT scans are not simple chest X-rays, which deliver only a small amount of radiation. Instead, they expose the patient to a significant amount of radiation, and radiation in significant doses has been shown to increase the risk of cancer.
We are all exposed to "natural background radiation" -- that is, radiation from the sun, radon gas, rocks in the ground, cosmic rays, and other sources that usually can't be avoided in our daily lives. Radiation is measured in units called "millisieverts" (mSv), and we can use millisieverts to compare this natural radiation to the levels of radiation we get from other sources, such as medical tests. For instance, a chest X-ray provides about 0.02 mSv, or the equivalent of 2.4 days of natural background radiation. A CAT scan of the abdomen, on the other hand, provides about 10.0 mSv, or the equivalent of 500 chest X-rays or 3.3 years of natural background radiation. And a 64-slice wholebody CAT scan provides 15.2 mSv for men and 21.4 mSv for women (women's denser body tissue and breasts require higher doses to get clear images) -- quite a difference, especially when you realize that the radiation you receive is cumulative.
Now compare these numbers with the level of radiation to which Japanese survivors of the atomic bomb explosions at Hiroshima and Nagasaki were exposed: an average dose of between 5 and 20 mSv, with some doses as high as 50 mSv. A single CAT scan can easily exceed that average. And since radiation from all sources remains in our bodies for life, the likelihood of the average twenty-first-century patient matching or exceeding that average, even without a CAT scan, is very high. In the New York Times, Roni Caryn Rabin reported that recent studies indicate that the amount of radiation in the bodies of Americans increased 600 percent between 1980 and 2006, with the bulk of this increase attributed to diagnostic imaging procedures. In 1980 about 3 million of these procedures were performed, but by 2006 the number had skyrocketed to 62 million.