Contrast agents are designed to mark things in the body so radiologists can detect them. In this case, the contrast agents marked bits of feces in the intestines, and a software program removed them from the image.
Several weeks later, the patients underwent regular colonoscopy, and the researchers compared the results.
The researchers found that the laxative-free colonoscopies were nearly as good as regular screenings at identifying polyps 10 mm or larger -- the most likely to become cancerous -- but were less effective at detecting smaller polyps. Common practice usually involves removing any polyps 6 millimeters or larger, the study authors said.
The virtual procedures do "an OK but not great job at finding larger polyps that everybody would agree need to be identified," said Dr. David Weinberg, chairman of medicine at Fox Chase Cancer Center in Philadelphia. "They do an even less good job at finding smaller polyps that might be significant."
Weinberg said there's still much to be understood regarding virtual colonoscopy, such as how often patients should undergo one to make sure polyps that are missed don't have a chance to grow to a dangerous size.
As for the idea of laxative-free virtual colonoscopy, he said, "the technique needs to continue to evolve before it's likely to be an important and frequently utilized alternative to colon cancer screening."
The study, funded in part by GE Healthcare, manufacturer of the contrast agent, appears in the May 15 issue of the Annals of Internal Medicine.
For more about colon cancer, visit the U.S. National Library of Medicine.
SOURCES: Michael E. Zalis, M.D., director, CT colonography, department of radiology, Massachusetts General Hospital, a
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