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Topic Overview

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.

Before this test, you will need to clean out your colon. The following information gives you a general idea of the preparation for a colonoscopy. Your doctor will give you specific instructions before your test.

• One to two days before a colonoscopy, you will stop eating solid foods and drink only clear fluids, such as water, tea, coffee, clear juices, clear broths, Popsicles, and gelatin (such as Jell-O).
• Your doctor will recommend a medicine for you to use to prepare for your colonoscopy. It will most likely be a prescription laxative tablet and/or a laxative solution (such as Nulytely or Golytely) that you drink before your colonoscopy. This solution will be given to you as a powder that you will mix with 1 gal (3.8 L) of water. You may need to drink this laxative solution over 1 to 2 hours in the evening before the test. Or you may be asked to drink half the solution the evening before your test and the other half the morning of your test. This solution may taste very salty and may make you feel sick to your stomach. To make your colon prep easier, you may want to try some of the following tips:
  • You may find it easier to drink the solution if you use a straw with the end at the back of your throat (to bypass the taste buds).
  • Each time you drink some of the solution, you may also drink some water or clear fluids (like apple juice) to help get rid of the salty taste in your mouth.
  • You may find it easier to drink the solution if you chill it in the refrigerator first.
  • Ask your doctor if it is okay for you to add flavored drink crystals (such as Crystal Light) to the solution.
  • Add lemon juice to the solution or suck on sliced lemon wedges after you take a drink.
• Your doctor may recommend a different preparation product, such as the Nutraprep meal kit or sodium phosphate tablets (for example, Visicol). These are other methods of preparing for a colonoscopy. If you are concerned about the bowel prep, you can ask your doctor whether another method will work for you.
  • Oral sodium phosphate (either tablets or liquid) can cause kidney problems. Make sure you check with your doctor before using a nonprescription sodium phosphate product.
• You will want to stay home while doing the colon prep because it will make you use the bathroom often.
• Drink plenty of clear fluids during the prep so you will not get dehydrated. This will also help clean out your colon completely after you finish the colon prep.
• Do not eat any solid foods after doing the colon prep.
• Stop drinking clear liquids 6 to 8 hours before the test.
• Your doctor may have you use an enema 30 to 60 minutes before the test to completely clean out your colon.

How is it done?

Virtual colonoscopy may be done in a doctor's office, clinic, or a hospital. The test is most often done by a doctor who specializes in performing and interpreting diagnostic imaging tests (radiologist). The doctor may also have an assistant.

You will need to take off most of your clothes. You will be given a gown to wear during the test.

First, you will be asked to lie on your back. Air (or in some cases, carbon dioxide) will be used to expand your colon. This helps the doctor see all parts of your colon. The air is added using a tube placed in your anus. It may be uncomfortable when the air is put into your colon. You may be given medicine to help the muscles in your colon relax.

You will be asked to hold your breath while the pictures of your colon are being taken. If you can't hold your breath for the whole time, the doctor may need to take pictures a couple times in order to get the whole colon. You may be asked to roll over and lie on your stomach. The doctor will ask you to hold your breath again and pictures will be taken with you lying in this position.

The test usually takes about 15 to 30 minutes.

How does a virtual colonoscopy differ from a regular colonoscopy?

Virtual colonoscopy has advantages and disadvantages compared to a regular colonoscopy.

Advantages

• Virtual colonoscopy is less invasive, safer, and takes less time than a regular colonoscopy.
• A thin tube to insert air into the colon is placed in the rectum rather than a long flexible tube that is moved up your colon. (But there is usually some discomfort when the air is inserted.)
• No medicine to relax or sedate you is needed, so you will be able to drive yourself home and resume normal activities.

Disadvantages

• Virtual colonoscopy may not show polyps smaller than 10 mm (0.4 in.).
• You will need to hold your breath for short periods of time while the computed tomography (CT) scanner takes pictures of your colon. CT scanning will need to be done twice: once while you lie on your back and then again while you lie on your stomach.
• Virtual colonoscopy is not covered by all health insurance plans. Check with your insurance plan before having the test.
• There is a small chance of developing cancer from having some types of CT scans.¹ If you are concerned about this risk, talk to your doctor about the amount of radiation this test may give you or your child and confirm that the test is needed.
• There is a slight risk that the CT scan can interfere with implanted or external medical devices. Examples of medical devices include pacemakers, insulin pumps, defibrillators, and neurostimulators.
• If a polyp is found, regular colonoscopy will be needed to confirm the diagnosis and remove the polyp so it can be looked at under a microscope. You will need to do another bowel preparation before the colonoscopy.

What do I need to consider about a virtual colonoscopy?

If you have an average risk for colorectal cancer, virtual colonoscopy may be an appropriate screening test for you. But if you are at an increased risk, you may require a regular colonoscopy because tissue biopsies or polyp removal can be done at the same time.

Virtual colonoscopy requires the same cleansing colon prep as a regular colonoscopy. If an abnormality is found on virtual colonoscopy, you may need a regular colonoscopy to remove and test the abnormal tissue. Since your colon is already clean, you may have the regular colonoscopy the same day.

Virtual colonoscopy is not available everywhere because it requires special equipment and special training to interpret the test. The initial evaluations on virtual colonoscopy were done by highly trained radiologists, so the results of your virtual colonoscopy may vary widely depending on the amount of experience your doctor's office or clinic has with the procedure.

Virtual colonoscopy is being studied to determine whether the results are as accurate (sensitivity) as a regular colonoscopy. More evidence is needed to show that virtual colonoscopy is a benefit in people with average risk for colon cancer and whether this screening method can prevent cancer. Colon preps that are more comfortable are also being studied.