Computed tomographic colonography (CTC) is a screening test that looks for signs of colorectal cancer. This test is also called a virtual colonoscopy.

A CT scanner takes X-ray pictures of your colon and rectum from outside your body. A computer arranges the pictures into a detailed image that can show polyps or other problems. Before the scan is done, the doctor inserts a thin tube into your rectum to fill your colon with air. Air in the colon makes polyps easier to see.

Sedation isn’t required, and the test itself doesn’t take much time. But a CTC requires the same bowel preparation as a colonoscopy.

If the doctor sees a problem during the test, such as a polyp or abnormal tissue, you will need to have a colonoscopy so a biopsy of the polyp or tissue can be done.