What to Expect During a Virtual Colonoscopy

female doctor by CT scan machine
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A virtual colonoscopy is a procedure used for diagnosing disease within the large intestine. The procedure involve the use of a CAT scan to take multiple x-ray images of your colon and rectum, which are then combined by a computer, allowing for a cross-sectional view of your entire large intestine. Less frequently, an MRI machine may be used. Virtual colonoscopy provides better images than a barium enema (lower GI series) and provides views of the colon not possible with conventional colonoscopy.

The test can show the presence of polyps, swollen tissue and ulcers.

Also Known As:

  • Colonoscopy - virtual
  • Computerized tomography (CT) colonography
  • CT colonography (CTC)

Difference from Conventional Colonoscopy

The virtual colonoscopy procedure differs from a conventional colonoscopy in that the interior of your colon is viewed through outside scans or images. In a conventional colonosopy, images are collected by a tiny camera at the end of the long tube that is inserted into the entire length of your colon. Thus, your doctor is viewing your colon from the inside. The conventional colonoscopy also allows for the removal of polyps and the taking of biopsies - two procedures that cannot be done with a virtual colonoscopy.

The virtual colonoscopy is also a less invasive test and you will not need to be sedated like you do in a conventional colonoscopy. Sometimes the virtual colonoscopy is recommended if the full scope of the large intestine is not able to have been seen during a conventional colonoscopy.

The virtual colonoscopy takes images of your entire abdomen, from your chest to your hips. Therefore it can show abnormalities in parts of your body beyond your large intestine.

Before the Procedure

Like a conventional colonoscopy, the virtual colonoscopy requires a complete emptying of your bowels. Therefore preparation for the test begins the day before your appointment.

You will not be allowed to eat solid food but must restrict your diet to clear liquids. You will be instructed as to which laxatives to use and when to use them so ast to ensure that your colon will be empty during the procedure.

You will be required to drink a substance that contains a contrast medium (a dye) that assists your doctor in distinguishing between stool and any polpys that might be present in your colon.

During the Procedure

The x-rays are painless. Pumping air into the colon may cause cramping or gas pains.

For the procedure you will be asked to lie on a table and a thin tube will be inserted into your rectum. (This differs from colonoscopy in which the tube is inserted into the entire length of your large intestine.) The tube used in virtual colonoscopy is much shorter and is used to pump air into your large intestine to enhance image clarity.

The table will then slide into a tunnel-like device that takes the X-rays. You may be asked to hold your breath at certain times. You will also be asked to shift onto your stomach or your other side so as to get varying views of your large intestine.

The whole procedure typically takes less than 20 minutes.

After the Procedure

If abnormal tissue is seen, a conventional colonoscopy can be performed the same day or shortly afterward for biopsy or removal.

Because you have not been sedated, you will not need to rely on someone else to accompany you home following the procedure. Following the procedure, you may feel bloated, experience some mild cramping and find yourself passing a lot of gas.

Risks of Virtual Colonoscopy

Overall, the virtual colonoscopy is seen as a generally safe procedures. The test does involve a low level exposure to radiation. There is also the risk of a tear in the lining of your colon, but this is an extremely rare occurence.

Limitations of Virtual Colonoscopy

Virtual colonoscopy is not widely used and may not be covered by your health plan. It is an alternative to traditional colonoscopy but is generally not considered by physicians to be an optimal option. In addition, if any tissue abnormalities or polyps are identified during the procedure, you may still need to undergo a conventional colonoscopy.


Bellows, C., Gagliardi, G. & Bacigalupo, L. "Review of computed tomographic colonography from a surgeon's perspective." Journal of Gastrointestinal and Liver Diseases 2015 24:215-23.

"Virtual Colonoscopy" National Institute of Diabetes and Digestive and Kidney Diseases Website accessed February 21, 2016.

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