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, although technology
exists to allow this procedure to be done without colon cleansing in some
circumstances. 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.
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 August 2014