Say you're told your chances of dying in a car crash are 1 in 16, but you can cut the odds way down if once every five years, starting at age 50, you spend a few hours having an expert check out your reflexes. Would you do it? Now substitute "colorectal cancer," which kills nearly 60,000 Americans a year, for "car crash" and "lower intestine" for "reflexes." The toll would be far lower if more people had a periodic colonoscopy, which allows a physician to examine the lining of the bowel after inserting a thin fiber optic tube. But relatively few do. The very idea tends to produce a visceral reaction.

So one of the hottest goals in radiology is to perfect virtual colonoscopy—visualization of the inside of the intestine from outside the body, using powerful CT scanners to spot potentially cancerous growths, or polyps, as effectively as if the exam was done the usual way. Nine studies presented at the Radiological Society of North America's annual meeting in Chicago this week addressed the marriage of computers with latest-generation CT scanners to locate and highlight problematic polyps. And the news is looking good.

The largest study, of 792 patients at three medical centers who received virtual and conventional colonoscopy the same day, found that CT scanning, coupled with computer-aided detection (CAD) software, was just about as good as picking up polyps of about 8 millimeters (about 0.3 inch) or larger as conventional colonoscopy was. The general rule is that polyps of at least 10 millimeters (about 0.4 inch) should be removed, and those 5 millimeters and below can be ignored.

The CAD-aided system used software created at the National Institutes of Health clinical center that creates detailed 3-D pictures of the intestinal lining and paints growths defined as polyps as bright blue. The study group had two cancerous polyps, both caught by the CAD system and one missed by the conventional method. Radiologist Ronald Summers, whose team at NIH wrote the CAD program, says it won't be too long before reliable virtual colonoscopy is available.

Eliminating the tube doesn't make the entire procedure virtual. Air has to be pumped into the lower bowel to inflate the tract; there would be no way to see anything if the walls of the tract were collapsed. And so far, at least, some kind of "bowel prep" is still necessary the evening before to clean out the lower intestinal tract. Summers notes that drinking a gallon of vilely salty solution, as many gastroenterologists and radiologists still prefer prior to the usual colonoscopy, can be reduced to a few spoons of liquid for the virtual version.

Even this may soon be eliminated. Liquids that "tag" waste products so that the computer knows to ignore them are being developed, and they are improving, Summers says. Soon every possible excuse to avoid having a colonoscopy may be gone.

See our guide on colorectal cancer for more information.