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 (colorectal cancer).

Virtual colonoscopy (more accurately called computed tomography colonography, or CTC) is a new test that is being studied to determine whether the results are as accurate as a regular colonoscopy. Since virtual colonoscopy is new, it is not widely available.

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, such as a barium enema test.
• Replace a regular colonoscopy if the thin lighted microscope tube 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).
• Evaluate the source of internal bleeding.
• Evaluate 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). Do not eat or drink red food items such as red juice or red 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.