CT Colonography

Woman over 50If you are 50 or older, or approaching that age, you are probably already aware that a colon screening is recommended every 7 to 10 years for that age group. The goal of a colon screening is to look for colonic polyps, which are growths in the inner lining of the large intestine that can potentially turn cancerous. When the growths are found in their early stages, they can be removed before cancer has had a chance to develop.

CT colonography is a minimally invasive procedure that offers a good alternative to traditional colonoscopy for many patients. The exam generally takes about 15 minutes, and no anesthesia is required.

How it works

A CT scanner is used to acquire images of the colon and then a sophisticated computer translates these into detailed three-dimensional pictures of the large intestine. These can be viewed as conventional CT images or as "virtual fly-throughs" of the large intestine, similar to how a traditional colonoscopy would look.

CT technology allows us to see the inside of the colon in the kind of detail otherwise found only in a traditional colonoscopy, in which a patient is sedated and an endoscope is snaked into the large intestine.

How to prepare

As with a traditional colonoscopy, a bowel preparation will be needed the night before a virtual colonoscopy. This will include taking laxatives to clear the colon, and drinking a barium solution that will help your doctor to see polyps more distinctly. You will also need to refrain from eating or drinking anything but small amounts of water beginning the night before the exam. Your doctor will discuss the preparation with you in further detail.

The CT colonography exam is performed on an outpatient basis, and you will be able to drive yourself home from the exam.

What to expect

You will wear a hospital gown during your exam. You will be asked to lie down on the CT examination table, usually flat on your back, but possibly on your side or stomach. The technologist will help position you, and pillows may be used to help you maintain the correct position throughout the brief exam.

A small, flexible tube will be passed two inches into your rectum. The tube is used to gently pump carbon dioxide into the colon to eliminate folds or wrinkles that could make it difficult to detect polyps during the exam. Carbon dioxide is quickly reabsorbed back into the body so feelings of bloating and pressure are markedly minimized.

Once the colon has been adequately distended, the scan will begin. The table will automatically begin to move through the opening in the scanner, and will continue to move as the actual CT scanning is performed. You will be asked to hold your breath for 15 seconds, then you will be repositioned on the table for a second trip through the scanner. After the second scan is complete, the tube will be removed, and you will be able to go home. No recovery time is needed after this procedure.


CT colongraphy is recommended by leading health organizations.

  • Colonography is one of four screening options for early detection of cancer and polyps recommended by the American Cancer Society, the American College of Radiology, and the U.S. Multi-Society Task Force on Colorectal Cancer. The organizations added the test to the recommended-procedure list in 2008, hoping to encourage more people to be screened.

CT colonography is easier on the patient than conventional colonoscopy.

  • Sedation and pain-relievers are not needed, so there is no recovery period.
  • Elderly patients, especially those who are frail or ill, may tolerate CT colonography better than conventional colonoscopy.
  • CT colonography has a markedly lower risk of perforating the colon than conventional colonoscopy. If no polyps are found, the patient will not have to undergo the more invasive traditional colonoscopy.

CT colonography is an excellent alternative for those who may face complications with conventional colonoscopy.

  • Clinical factors such as treatment with a blood thinner or a severe breathing problem may increase the risk of complications from conventional colonoscopy, but will not cause any risk for CT colonography.
  • CT colonography can be helpful when a conventional colonoscopy can't be completed because the bowel is narrowed or obstructed for any reason, such as by a large tumor. Patients can be moved directly from the operating room to the CT scanner if it is found that a traditional colonoscopy cannot be completed, allowing the patient to avoid a second bowel preparation regimen.

CT colonography is less costly than colonoscopy.

  • Community Hospital's Patient Access department will be happy to consult your insurance company to help you calculate the out-of-pocket costs of your screening. Keep in mind, some insurance will not cover CT colonography as a screening test for colonic polyps. Call (831) 625-4596 to learn more.

Possible risks

If polyps are found, you may still have to undergo the more invasive traditional colonoscopy.

If no polyps or polyps measuring less than 6mm are found, no additional screening is necessary. If polyps measuring 6 to 8mm are found, you will be given the option to have them removed with traditional colonoscopy, or to follow up with another CT colonoscopy screening in 1-2 years.  If a polyp of 8mm or larger is found, biopsy by colonoscopy is recommended, and you may be given the option to be taken directly to the operating room.

Exposure to radiation

CT scans utilize a small amount of radiation, however, a CT scan uses no more radiation than a traditional X-ray, and care is taken to use the lowest dose of radiation possible while producing high-quality images.