Digestive Disorders Health Center

What is a virtual colonoscopy?

A virtual colonoscopy uses X-rays and computers (computed tomography [CT] or magnetic resonance imaging [MRI]) to take two- or three-dimensional images of the interior lining of your large intestine (colon) and rectum. A virtual colonoscopy can be used to screen for precancerous and cancerous growths in the colon or rectum (colorectal cancer), such as polyps or tumors.

Virtual colonoscopy (also called computed tomographic colonography, or CTC) is still being studied to determine whether the results are as accurate as a regular colonoscopy. Virtual colonoscopy is not yet widely available.

Virtual colonoscopy is one of many tests that may be used to screen for colon cancer. Which screening test you choose depends on your risk, your preference, and your doctor. Talk to your doctor about what puts you at risk and what test is best for you.

For more information on screening tests for colon cancer, see:

Colon Cancer: Which Screening Test Should I Have?

Why is it done?

A virtual colonoscopy may be done to:

• Screen for colorectal cancer or polyps.
• Monitor the growth of polyps.
• Screen for recurrence of colorectal cancer in people who have had surgery for this disease.
• Evaluate abnormal results from other colon tests.
• Replace a regular colonoscopy if the thin lighted scope cannot be inserted in the colon for some reason, such as when a tumor blocks the passage.

Virtual colonoscopy is not commonly done for other conditions at this time but may prove to be useful to:

• Detect other problems or diseases of the anus, rectum, or large intestine (colon).
• Check the source of internal bleeding.
• Check the cause of chronic diarrhea.
• Monitor the treatment of inflammatory bowel disease.

How do I prepare for it?

Virtual colonoscopy requires the same cleansing colon prep as a regular colonoscopy. Colon prep takes 1 to 2 days depending on which type of prep your doctor recommends. For many people, the prep for a colonoscopy is more trying than the actual test. Researchers are studying methods that could be used to mark (tag) stool in the colon before virtual colonoscopy so cleansing colon preps would not be needed.

One to two days before a colonoscopy, you will need to stop eating solid foods and drink only clear liquids, such as water, tea, coffee, clear juices, clear broths, Popsicles, and gelatin (such as Jell-O).

Some preps, such as taking a prescription laxative tablet or drinking a laxative solution (such as Nulytely or Golytely), are done the evening before your colonoscopy. The colon prep causes loose, frequent stools and diarrhea so that your colon will be empty for the test. Plan to stay home during your prep time since you will need to use the bathroom frequently. The colon prep may be uncomfortable, and you may feel hungry on the clear liquid diet. If you need to drink a laxative solution, be sure to have clear fruit juices or soft drinks to drink after the prep because the solution tastes salty.