THE QUESTION People who have a virtual colonoscopy, which is done by CT scan, still have to undergo a traditional bowel cleansing to clear the colon and allow accurate detection of polyps. A new method uses computer software to adjust the CT image of the intestines, negating the need for a laxative-induced cleansing. Might that technique be a viable alternative?

THIS STUDY involved 605 adults, 60 years old, on average, who were considered at moderate risk for colon cancer and were screened twice. For two days before the first test — a virtual colonoscopy — they ate a low-fiber diet, adding to some foods a contrast material that would “tag” fecal matter in their intestines. After the CT scan was done, special software removed the tagged material from the images, which were then checked for suspicious polyps. A few weeks later, participants underwent the second test, a standard colonoscopy, which used a flexible scope to check for polyps. They restricted fiber intake for a day or two before the test, and on the night before the exam, they drank the requisite laxative preparation to purge their intestines. The image-cleansing method was nearly as good as the traditional in identifying larger polyps, which are considered the most likely to become cancerous: The CT test found 91 percent of the growths that were 10 millimeters or larger vs. 95 percent for the standard colonoscopy. But the new technique was less accurate for smaller polyps measuring at least 6 millimeters, finding 59 percent vs. 76 percent. Participants found the laxative-free preparation easier, and the majority indicated they would prefer it for future screening.

WHO MAY BE AFFECTED? Adults. About one of every 20 adults develops colorectal cancer, but deaths from the disease are declining, in part because of screenings that can detect growths before they become cancerous. Periodic screening is suggested from age 50 on. Studies have found that 90 percent of polyps likely to become cancerous are 10 millimeters or larger; common medical practice is to remove growths of 6 millimeters or more.

CAVEATS The authors noted that the doctors’ experience and “interpretation technique may have greater influence” in evaluating the cleansed images. The technique is considered experimental by some and may not be widely available.

FIND THIS STUDY May 15 issue of Annals of Internal Medicine (

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Linda Searing

The research described in Quick Study comes from credible, peer-reviewed journals. Nonetheless, conclusive evidence about a treatment's effectiveness is rarely found in a single study. Anyone considering changing or beginning treatment of any kind should consult with a physician.