Virtual Colonoscopy

Overview

Virtual colonoscopy, called CT colonography at Mayo, is used to detect colon and rectal cancer noninvasively. CT colonography uses a CT scanner and special computer software to produce detailed three-dimensional images of the colon and rectum. CT colonography is available at Mayo Clinic in Minnesota and Arizona.

A study published in the New England Journal of Medicine in 2003 reported that CT colonography is approaching the accuracy of traditional colonoscopy in detecting polyps that may indicate cancer. Studies also indicate that accuracy varies depending on the experience of the radiologist reviewing the images.

Mayo Clinic has been at the forefront in using and studying CT colonography since its inception in 1995. Mayo Clinic was the first institution to report in the scientific literature on the clinical effectiveness of this technique, and the first to offer it for routine care. Physicians at Mayo Clinic in Minnesota and Arizona have performed more than 4,000 CT colonographies, more than any other medical center.

Advantages of CT Colonography

• Less invasive than colonoscopy
• Quicker than colonoscopy
• No sedation required
• Minimal risk of bleeding or perforation of colon or rectum. This may be an important consideration for patients on blood-thinning medications
• Useful for patients who have suspected colon or rectal obstruction
• An alternative for patients unwilling to undergo colonoscopy

The Procedure

Virtual colonographic view of the interior of the colon

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Patients must follow the same bowel-cleansing routine used for colonoscopy. This involves drinking about a gallon of a special laxative liquid the day before the examination. On the day of the exam, patients are first given an injection of medication that relaxes the bowel. Once inside the CT room, patients are placed on their side and a small enema tip is placed in the rectum and carbon dioxide gas is slowly introduced into the colon. This continues until the patient feels full. The gas expands the colon in order to get the best possible images. The CT scans are made with the patient in two positions. Each scan takes about 20 seconds. The total time in the exam room is about 10 minutes.

If polyps are seen, a patient at Mayo may undergo a colonoscopy to remove the polyps the same day. Patients are encouraged to speak with their ordering physician for this scheduling option. This averts the need for another round of bowel preparation.