This test can find both colorectal polyps and cancer.

This test is an advanced type of computed tomography (CT) scan of the colon and rectum that produces cross-sectional images of your body. A CT scanner takes many pictures as it rotates around you while you lie on a table. A computer then combines these pictures into images of slices of the part of your body being studied. For CT colonography, computer programs create both two dimensional x-ray pictures and a three-dimensional "fly-through" view of the inside of the colon and rectum, which allows the doctor to look for polyps or cancer.

This test may be appropriate for people who can't have or don't want to have more invasive tests. The test still requires a type of bowel preparation and uses a tube placed in the rectum to fill the colon with air. It can be done fairly quickly and does not require sedation. A possible drawback is that if polyps or other suspicious areas are seen on this test, a colonoscopy will still likely be needed to remove them or to explore them fully.

Before the test: It is important that the colon and rectum are emptied before this test to provide the best images. You will likely be instructed to follow a clear liquid diet for a day or two before the test, and to take strong laxatives and/or enemas the night before or morning of the exam.

During the test: This takes about 10 minutes. You may be asked to drink a contrast solution before the test to help "tag" any remaining stool in the colon or rectum, which helps the doctor when looking at the test images. You will lay on a thin table that is part of the CT scanner, and will have a small, flexible tube inserted into your rectum. Air is pumped through the tube into the colon to expand it to provide better images. The table then slides into the CT scanner and you will be asked to hold your breath while the scan takes place. You will likely have two scans: one while you are lying on your back and one while you are on your stomach. Each scan typically takes only about 10 to 15 seconds.

Possible side effects: Many people consider the bowel preparation to be the most unpleasant part of the test, as it usually requires you to be in the bathroom quite a bit. With the CT colonography itself, there are usually very few side effects. You may feel bloated or have cramps because of the air in the colon, but this should go away once the air passes from the body. There is a very small risk that inflating the colon with air could injure or puncture the colon.