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Virtual colonoscopy

Contents of this page:

Alternative Names   

Colonoscopy - virtual; CT colonography

Definition    Return to top

Virtual colonoscopy (VC) combines MRI or CT scans with sophisticated computer software to produce three-dimensional images of the colon and rectum. The test is less invasive than conventional colonoscopy.

How the Test is Performed    Return to top

Patients must follow a strict bowel-emptying procedure the day before, just as they would for a standard colonoscopy. The test is performed in the radiology department of a hospital or medical center. Unlike conventional colonoscopy, no sedatives are needed and no scope is used.

You will lie down on your left side on a narrow table that is connected to an MRI or CT machine. Your knees will be up toward your chest. A small, flexible tube will be inserted into your rectum. Air is pumped through the tube to make the colon bigger and easier to see. After this is done, you’ll be asked to lie on your back.

Next, the table slides into a large tunnel through the machine, where x-rays create images of your colon. You must stay very still during this procedure, since movement can blur the pictures. You may be asked to hold your breath briefly while each picture is taken.

A computer combines all the images to form three-dimensional pictures of the colon, which are viewed on a video monitor.

Pictures are also taken while you lie on your stomach.

The exam takes about 20 minutes.

How to Prepare for the Test    Return to top

Preparations can vary, depending on your health care provider. Everyone undergoing any type of colonoscopy must completely empty their bowels before the exam. This may be done using an enema or laxatives combined with a liquid diet the day before the test. The bowel must be completely emptied until no solid matter remains.

Unfortunately, diarrhea is common during preparation. Drink plenty of clear liquids, such as apple juice and chicken broth, to avoid dehydration.

Make sure you tell your health care provider about any medications you are taking. You’ll be told which you can take, and which you should temporarily stop. CT and MRI scanners are very sensitive to metals. Don’t wear jewelry the day of your exam. You’ll be asked to wear a hospital gown for the procedure.

How the Test Will Feel    Return to top

The x-rays are painless. Pumping air into the colon can create temporary cramping or gas pains.

Why the Test is Performed    Return to top

Virtual colonoscopy may be performed to:

Normal Results    Return to top

Normal findings are images of a healthy intestinal tract.

What Abnormal Results Mean    Return to top

Risks    Return to top

Considerations    Return to top

Differences between virtual and conventional colonoscopy include:

Virtual colonoscopy is now one of the American Cancer Society's recommended screening tools for colon cancer.

References    Return to top

Lieberman, D. Colonoscopy: as good as gold? Ann Intern Med. 2004;141:401-403.

Pickhardt P, et al. Location of adenomas missed by optical colonoscopy. Ann Intern Med. 2004;141:352-359.

Rosman AS, Korsten MA. Meta-analysis comparing CT colonography, air contrast barium enema, and colonoscopy. Am J Med. 2007;120(3):203-210.e.4.

Van Dam J, et al. AGA future trends report: CT colonography. Gastroenterology. 2004;127:970-984.

Virtual colonoscopy. Med Lett Drugs Ther. 2005;47(1202):15-16.

Update Date: 3/8/2008

Updated by: Christian Stone, MD, Division of Gastroenterology, Washington University in St. Louis School of Medicine, St. Louis, MO. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

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