CT colonography, also known as virtual colonoscopy, utilizes the X-ray technology of a CT scan combined with computer software to create an image of the inside of the colon (large intestine). In addition, views of the other intra abdominal organs are obtained. These images can be configured to resemble what one would see during a colonoscopy. Colonoscopy, by contrast, looks directly at the inside of the colon through a video endoscope passed through the anus into the colon.
CT colonography is performed and interpreted by radiologists in most circumstances. The test is similar to colonoscopy in that the bowel must be cleansed of fecal material prior to the scan. The colon is distended by air or carbon dioxide introduced through the rectum, and the CT scan is completed over approximately 10 minutes. CT colonography is done without sedation. If polyps are found on CT colonography, colonoscopy will then be necessary to remove the polyps. Colonoscopy is the only method that allows for both the detection and removal of polyps.
Recent studies show that CT colonography is effective in identifying medium to large polyps, but may be ineffective in identifying small polyps. CT colonography may be best for low-risk patients who cannot undergo or who failed a conventional colonoscopy. The procedure is not currently covered by Medicare as an initial screening test.
Reviewed November 2010