What is a CT colonography (virtual colonoscopy)?

Daniel D. Cho, MD
A virtual colonoscopy is a specialized computed tomography (CT) scan that allows the radiologist to visualize the colon. This test is useful in the detection of polyps and colorectal cancer. Studies have confirmed the accuracy of this test in comparison with other screening modalities.

The advantage is that this test does not require sedation and is less invasive. The drawbacks are that you will still have to take a bowel prep the night before the exam, and should a polyp be detected, you will still have to undergo a standard colonoscopy. Currently, this test is not universally covered by all insurance plans. Also, as with other CT scans, there is a small degree of radiation exposure.

The test is recommended at five-year intervals.
A CT colonography is an advanced type of computed tomography (CT or CAT) scan of the colon and rectum. A CT scan is an x-ray test that produces detailed cross-sectional images of your body. Instead of taking one picture, like a regular x-ray, a CT scanner takes many pictures as it rotates around you while you lie on a table. A computer then combines these pictures into images of slices of the part of your body being studied. For CT colonography, special computer programs create both two dimensional x-ray pictures and a three-dimensional "fly-through" view of the inside of the colon and rectum, which allows the doctor to look for polyps or cancer.
This test may be especially useful for some people who can't have or don't want to have more invasive tests such as colonoscopy. It can be done fairly quickly and does not require sedation. But even though this test is not invasive like colonoscopy, it still requires the same type of bowel preparation and uses a tube placed in the rectum (similar to the tube used for barium enema) to fill the colon with air. Another possible drawback is that if polyps or other suspicious areas are seen on this test, a colonoscopy will still likely be needed to remove them or to explore them fully.
CT colonography is a CT scan, or a radiology test. It's an x-ray of the colon. It can be a very useful test, but some people aren’t aware that to have this test they still need to do an entire bowel cleanse.

There is also a small risk of perforation, which is also a risk with colonoscopy. Here’s the other caveat: If a polyp is found on your CT colonography, you have to have a colonoscopy and you have to do a bowel cleanse again. But if we're doing this test because we could not get to the end of your colon with a colonoscopy, which is rare but possible, this may be a good test.

CT colonography was rising in popularity along with the flat polyp phenomenon. But there’s really been no evidence that’s shown whether the CT colonography is even good at detecting flat colon polyps.
Dr. Mehmet Oz, MD
Cardiology (Cardiovascular Disease)
Virtual colonoscopy (computerized tomographic colonography) is a new type of screening method that uses a CT scanner to visualize the colon. A device is inserted at the rectum but does not ascend up past the sigmoid portion of the colon. It is less uncomfortable but a colonoscopy will still be required if a polyp is found. Bowel prep is still necessary.
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A traditional colonoscopy has the ability to not just identify polyps, but remove them, so a traditional colonoscopy and virtual colonoscopy are not really equivalent. A virtual colonoscopy is more like a barium enema or a high-tech lower GI x-ray. Because of the limitations with a virtual colonoscopy, the current consensus is that virtual colonoscopy is not ready for "prime time", however, this may be an option in the future.
CT colonography, also referred to as virtual colonoscopy, relies on a computer program to generate a 3D picture of the large intestine (colon) using x-ray images. This differs from colonoscopy, which provides actual photos of the colon and rectum via a camera attached to a thin, flexible scope that is physically guided through the large intestine.

With virtual colonoscopy, a small tube is placed in the rectum and air is pumped into the colon to inflate the bowel. Then a special CT scan is used to image the colon. Studies show that it is effective in identifying medium to large polyps, but is ineffective in identifying small polyps. CT colonography may be best for low-risk patients who cannot undergo or who failed a conventional colonoscopy. The same bowel prep as conventional colonoscopy is required and it does not use sedation. The procedure uses X-ray radiation and if polyps or other abnormalities are found, a conventional colonoscopy must be performed. Virtual colonoscopy is not covered by Medicare or most other payers as an initial screening test.
Daniel Labow, MD
Surgical Oncology

Virtual colonoscopy uses specialized CT Scan images to examine the colon, so it does exposes the patient to the radiation of a CT Scan. It can be very accurate, but it does not allow for any biopsies. If an abnormality is found, a regular colonoscopy is needed. In addition, patients must prepare for a virtual colonoscopy in the same way they prepare for a traditional colonoscopy as the colon must be completely clean so the doctor has a clear view of your intestines.   

Donald Petroski, MD
CT (computed tomography) colonography, also known as virtual colonoscopy, is an option to screen for colorectal cancer. This test uses special x-ray equipment to produce pictures of the colon and the rectum from outside the body. A computer then assembles these pictures into detailed images that can show polyps and other abnormalities.

Virtual colonoscopy does not require sedation. As with standard colonoscopy, a thorough cleansing of the colon is necessary before this test. If polyps or other abnormal growths are found during a virtual colonoscopy, a standard colonoscopy is usually performed to remove them.
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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.