Conditions and Procedures

Virtual colonoscopy


Virtual colonoscopy is a less invasive way to check for cancer of the large intestine. Virtual colonoscopy is also known as screening CT colonography.

Unlike the usual or traditional colonoscopy, which needs a scope to be put into your rectum and advanced through your colon, virtual colonoscopy uses a CT scan to take hundreds of cross-sectional pictures of your belly organs. The pictures are then added together to provide a complete view of the inside of the colon and rectum. Virtual colonoscopy needs a similar bowel cleaning as a usual colonoscopy.

Virtual colonoscopy is one way to check for colon cancer. Discuss your colon cancer screening choices with your health care provider to see if virtual colonoscopy is the right choice for you.

Why it's done

Virtual colonoscopy is used to check for colon cancer in people who are at least 45 years old.

Your health care provider may suggest a virtual colonoscopy if you:

  • Are at an average risk of colon cancer.
  • Do not want medicine that puts you to sleep or you need to drive after the test.
  • You don't want to have a colonoscopy.
  • Are at risk of colonoscopy side effects, such as a lot of bleeding because your blood doesn't clot in the usual way.
  • Have a bowel blockage.

You aren't able to have a virtual colonoscopy if you have:

  • A history of colon cancer or unusual tissue clumps called polyps in your colon.
  • A family history of colon cancer or colon polyps.
  • Chronic painful and swollen bowel disease called Crohn's disease or ulcerative colitis.
  • Acute diverticulitis.

Studies have shown that virtual colonoscopy finds large polys and cancer at about the same rate as usual colonoscopy.

Because virtual colonoscopy looks at the entire abdomen and pelvic area, many other diseases may be found. Problems unrelated to colon cancer such as irregularities in the kidneys, liver or pancreas can be detected. This may lead to more testing.


Virtual colonoscopy is generally safe. Risks include:

  • Tear (perforation) in the colon or rectum. The colon and rectum are pumped with air or carbon dioxide during the test and this carries a small risk of causing a tear. However, this risk is lower compared with that of traditional colonoscopy.
  • Exposure to a low level of radiation. Virtual colonoscopy uses a small amount of radiation to make the pictures of your colon and rectum. Health care providers use the lowest amount of radiation possible to take a clear picture. This is about the same as the amount of natural radiation you might be exposed to in two years, and much less than the amount used for a regular CT scan.

How you prepare

Not all health insurance providers pay for virtual colonoscopy for colon cancer screening. Check with your health insurance provider to see which tests are covered.

What you can expect

Before the test

Before a virtual colonoscopy, you'll need to empty your colon. Any bowel movement, or stool, left in your colon may cloud the pictures taken during the exam.

To empty your colon, follow your health care provider's instructions carefully. You may be asked to:

  • Follow a special diet the day before the exam. Typically, you won't be able to eat that day. Drinks may be limited to clear liquids. You may not be able to eat or drink anything after midnight the night before the exam.
  • Take a laxative the night before the exam. You may also need to use a suppository to clear any remaining bowel movement in your colon.
  • Take medicine to identify stool in your colon. The medicine will help the health care provider see the difference between colon irregularities and stool.
  • Adjust your usual medicines. Remind your health care provider of your medicines at least a week before the exam. For a short amount of time, you may need to stop taking certain medicines days or hours before the exam.

During the test

You'll wear a gown but likely no other clothes. Medicine to put you to sleep usually isn't necessary, but you may be given medicine to relax your colon.

You'll begin the exam lying on your side on the exam table, usually with your knees drawn toward your chest. A nurse or technologist will place a small tube called a catheter inside your rectum. Through this catheter, your colon will be filled with air or carbon dioxide as you roll over on the table while keeping your spine straight. The air or gas helps create clear pictures and may cause a feeling of pressure in your stomach area.

For the next part of the exam, you'll lie on your back. The exam table will be moved into the CT machine, and your body will be scanned. Then you'll turn over to lie on your belly or your side and your body will be scanned again.

You may be asked to turn and hold some other positions as well as hold your breath at times.

A virtual colonoscopy typically takes about 15 minutes.

After the test

You can restart your usual activities after your virtual colonoscopy. You may feel bloated or pass gas for a few hours after the exam as you clear any remaining air or gas from your colon.


Your health care provider will go over the results of the colonoscopy and then share them with you.

Your test results may be:

  • Negative. This is when the health care provider doesn't find any irregularities in the colon. If you're at average risk of colon cancer and you have no colon cancer risk factors other than age, your doctor may suggest repeating the exam in five years.
  • Positive. This is when the pictures show polyps or other irregularities in the colon. If these findings are seen, your health care provider will likely suggest a traditional colonoscopy to get samples of the irregular tissue or remove the polyps. In some cases, the traditional colonoscopy or polyp removal can be done the same day as the virtual colonoscopy.
  • Finding other irregularities. Here, the imaging test finds problems outside the colon, such as in the kidneys, liver or pancreas. These findings may or may not be important, but your health care provider may suggest additional testing to find their cause.

Updated on Jul 6, 2023