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Virtual Colonoscopy

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 intestineClick here to see an illustration. (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.



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


Why is it done?

A virtual colonoscopy may be done to:

  • Screen for colorectal cancer or polyps.
  • Monitor the growth of polyps.
  • Evaluate abnormal results from other colon tests.


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 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).
    • 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.
  • 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.
  • You will want to stay home while doing the colon prep because it will make you use the bathroom often.
  • 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?



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.


  • 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.)


  • 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.
  • 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.
  • 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?


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.



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