Future Virtual Colonoscopy Could Be Laxative-Free

The CTC included electronic cleansing and computer-aided detection.

Optical colonoscopy examinations were initially blinded to CTC results, which were subsequently revealed during colonoscope withdrawal. For two days before the CTC scans, the volunteers drank small amounts of a contrast agent with their meals, which chemically tagged the stool, allowing the software to detect it and subtract it from the computerized tomography (CT) scan.

The laxative-free CTC method was accurate in detecting adenomas 10 mm or larger in 91% of the patients with precancerous polyps, but was less accurate for smaller lesions. Patient experience was better with laxative-free CTC, which is about as accurate as conventional colonoscopy. According to the researchers, these results suggest a possible role for laxative-free CTC as an alternate screening method. The study was published in the May 15, 2012, issue of Annals of Internal Medicine.

“The trouble is a lot of the people at risk of colorectal cancer have a strong aversion to the laxative prep that is required for colonoscopy,” said lead author Michael Zalis, MD, an associate professor of radiology at MGH and director of CTC. “Laxative-free CT colonography has the potential to reach some of the unscreened population and save lives.”

CTC is an imaging procedure that produces images of the colon from the rectum, all the way to the cecum, and provides 3D reconstructed endoluminal views of the bowel. The procedure is used to diagnose colon and bowel disease, including polyps, diverticulosis, and cancer. The main disadvantage to CTC is that a radiologist cannot remove polyps, so a conventional colonoscopy must be performed if abnormalities are found. Also, it does not show as much detail as a conventional colonoscopy, so polyps smaller than 2-10 millimeters in diameter may not show up on the images.

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