Computed tomographic colonoscopy (CTC) is sometimes referred to as virtual colonoscopy. It uses a series of multiple x-ray images or slices, reassembled by computer, to give an picture of the interior of the colon.
How your colon looks on CTC.
Image courtesy of RadiologyInfo.
Similar to any CT scan, the patient lies on a table that moves through a large round machine with rotating scanners. Before the test begins, a small tube is inserted into the rectum and either air or carbon dioxide is infused into the colon to expand it slightly, eliminating wrinkles and making it easier to see polyps. Patients usually are able to control air insertion themselves using a small hand pump.
Typically the test takes about ten minutes. Sedation isn’t used so there is no recovery time afterward. Patients can drive themselves home and return to work or other activities right away.
Like traditional optical colonoscopy the colon must be completely clear of any stool for the most effective test. So very similar preparation – clear liquids and strong laxatives – are necessary before CT colonography.
If polyps or other suspicious areas are found during CTC, follow-up optical colonoscopy is necessary to remove polyps or biopsy potential cancers. In some settings, radiologists and gastroenterologists are working together to schedule an follow-up optical colonoscopy on the same day to avoid a second colon cleansing prep. In recent studies, about eight to ten percent of patients required that follow-up optical exam.
Pooled studies have found CT colonography as sensitive as optical colonoscopy for finding large polyps and cancers. It is somewhat less sensitive for smaller ones. One concern is whether CTC can identify flat or depressed nonpolypoid colorectal neoplasms, which were found in about six percent of people being screened in one colonoscopy study and are more likely to turn into cancer than polyps.
CT colonography was added to the recommended screening guidelines as a test to detect adenomatous polyps and cancer in March 2008.
Where Can You Go for More Information
CT Colonography information for patients on RadiologyInfo sponsored by the American College of Radiology (ACR) and the Radiological Society of North America (RSNA).