Definition and Overview

Virtual colonoscopy or CT colonography is an imaging test of the colon that generates multiple cross-sectional photos using CT scan. It can be helpful in providing a more detailed image of the colon including the rectum, especially if the presence of polyps, which can be pre-cancerous, is suspected.

This type of test is different from standard colonoscopy, which uses a long flexible tube inserted into the rectum all the way to the colon to check for polyps.

Who Should Undergo and Expected Results

Virtual colonoscopy may be carried out if the patient develops gastrointestinal-related illnesses or symptoms like:

  • Bleeding during bowel movement
  • Changes in bowel movement
  • Abdominal pain or cramps
  • Unexplained weight loss
  • Frequent passing of gas
  • Bloating
  • Feeling of satiation despite eating small meals

It may also be suggested if the person has gone through a fecal occult blood test (FOBT), a routine exam that can identify the presence of blood in the collected stool sample. The CT scan is therefore needed for further diagnosis or investigation.

People who are at least 50 years old are recommended to undergo colon cancer screening test, of which the interval varies on the actual test performed. Those whose condition is familial may have to go through the testing much earlier and more often than the general population.

The actual scanning takes only a few minutes, but the entire process may last for at least an hour. The scan must be able to determine the condition of the colon including the presence of polyps.

How Does the Procedure Work?

A gastroenterologist recommends the procedure to the patient based on the results of previous medical tests and symptoms. The patient schedules the scan as certain preparations have to be carried out. These include the intake of a special type of fluid to cleanse the colon. There are also diet restrictions. A day before the exam, the patient can only consume liquids.

During the actual exam, a technologist will assist the patient as he is positioned on a flat table. Gas is introduced through the rectum using an electric pump or a flexible tube. The air will ensure that the colon is distended. Straps are also attached to the body to keep the person from moving during the scan.

The table then goes through the scanner. When the technician is ready to take images, the patient may have to hold his breath for at least 15 seconds. Through a speaker and a microphone, the technician communicates from the other room and instructs the patient on what else to do.

After the exam, the radiologist analyzes the images gathered. If there’s a polyp, the patient proceeds to regular colonoscopy to remove it.

Possible Risks and Complications

Virtual colonoscopy is less sensitive to polyps measuring less than 7mm. It is possible to miss out certain precancerous polyps, especially if the radiologist doesn’t have enough experience in performing the procedure.

Going through CT colonography doesn’t immediately eliminate the need for regular colonoscopy (which is more invasive), particularly since it’s the only way to remove the polyps so they can be taken to the lab for biopsy.


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  • National Comprehensive Cancer Network. NCCN Clinical Practice Guidelines in Oncology (NCCN Guidelines): Colorectal cancer screening. Version 1.2014. Available at: Accessed February 12, 2015.

  • U.S. Preventive Services Task Force. Screening for colorectal cancer: U.S. Preventive Services Task Force recommendation statement. Ann Intern Med. 2008;149:627-637. PMID 18838716. Available at:

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