What is Virtual Colonoscopy (CT Colonography)?

Virtual Colonoscopy or CT colonography is a non-invasive, highly accurate test that allows doctors to look at the large bowel (colon) to detect polyps and cancers in the early stages. It is a screening technique that uses a CT scanner and computer graphic software to produce images of the colon through which the radiologist can “navigate.” Colon cancer can be prevented if polyps are discovered and removed early. Virtual Colonoscopy enables early detection of polyps and cancers.

What are some common uses of the procedure?

The major reason for performing Virtual Colonoscopy is to screen for polyps or cancers in the large intestine. Polyps are growths that arise from the inner lining of the intestine. A very small number of polyps may grow and turn into cancers. The goal of screening with Virtual Colonoscopy is to find these growths in their early stages. This allows the doctor to remove them before cancer has a chance to develop.

The American Cancer Society (ACS) recommends that women and men undergo screening for colon cancer or polyps beginning at age 45. As part of its recommendation, ACS suggests Virtual Colonoscopy as an option once every five years. Individuals at increased risk or with a family history of colon cancer may start screening at age 40 or younger and may be screened at shorter intervals (for example, having a colonoscopy every five years). Risk factors for the disease include a history of polyps or having a family history of colon cancer. Signs and symptoms of colon cancer include a persistent change in bowel habits, the presence of blood in the stool, abdominal discomfort or pain, bloating and unexplained weight loss.

The American Cancer Society recommends patients seek colorectal cancer screening as early as age 50 and every 3-5 years thereafter. Patients with a family history of colorectal cancer or polyps should be screened more often.

Why is Virtual Colonoscopy an excellent alternative to conventional colonoscopy?

In conventional colonoscopy, a long thin scope is inserted into the colon (rectum). This procedure typically uses sedation for the patient’s comfort. A tiny camera in the scope transmits images of the colon to a monitor for the doctor to review. The total procedure time is 30-60 minutes. Virtual Colonoscopy is more comfortable than a conventional colonoscopy screening because it does not require a colon scope or sedation. The exam also takes less time. Another advantage of Virtual Colonoscopy is that organs surrounding the colon can also be screened for abnormalities. Sometimes conventional colonoscopy may result in an incomplete exam due to bowel obstructions. There is a slightly greater chance of having a complete exam with a Virtual Colonoscopy. A conventional colonoscopy may be needed to investigate abnormalities discovered on the virtual exam.

How should I prepare for this procedure?

This procedure requires oral preparations to clear stool from your colon. The bowel-cleansing regimen for Virtual Colonoscopy may be similar to that for a colonoscopy or consist of a smaller volume of cleansing liquid. Your diet will be restricted to clear liquids the day before the exam. It is very important to clean out your colon the night before your exam so that the radiologist can clearly see any polyps that might be present. You will take either a set of pills and/or a liquid laxative. You may take additional agents the day before the exam. These may include small quantities of barium and iodinated liquids. These agents help the radiologist better distinguish stool from polyps by "tagging" the remaining stool and fluid. An oral contrast medium is also taken the day prior to your scan.

Be sure to inform your doctor if you have heart, liver, or kidney disease to be certain that the bowel prep will be safe. You will be able to resume your usual diet immediately after the exam. 

How does the procedure work?

During CT scanning, several x-ray beams and electronic x-ray detectors rotate around you.  Sometimes, the exam table will move during the scan, so that the x-ray beam follows a spiral path. A special computer program processes this large volume of data to create cross-sectional images of your body.

For Virtual Colonoscopy, the computer generates a detailed three-dimensional (3-D) model of the colon, which the radiologist uses to view the bowel in a way that simulates traveling through the colon. This is why the procedure is called a virtual colonoscopy. Two-dimensional (2-D) images of the inside of the colon as well as the rest of the abdomen and pelvis are also obtained and reviewed at the same time without any additional radiation. 

What can I expect during this procedure?

The technologist begins by positioning you on the CT exam table, first lying flat on your back then lying on your stomach. Once comfortable a very small, flexible tube will be inserted two inches into your rectum and air will be gently pumped into the colon. The purpose of the air is to distend (inflate) the colon as much as possible to eliminate any folds or wrinkles that might hide polyps from the radiologists' view.

Next, the table will move through the scanner. The technologist may ask you to hold your breath for about 15 seconds before turning over and lying on your stomach for a second pass through the scanner. Once the scan is done, the technologist will remove the tube.

The entire exam usually takes about 15 minutes. Following Virtual Colonoscopy, you can immediately return to your normal activities.

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