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Virtual Colonoscopy

Virtual colonoscopy (VC) is a Medical imaging procedure which uses x-rays and computers to produce two- and three-dimensional images of the colon (large intestine) from the lowest part, the rectum, all the way to the lower end of the small intestine and display them on a screen. The procedure is used to diagnose colon and bowel disease, including polyps, diverticulosis and cancer. VC can be performed with computed tomography (CT), sometimes called a CAT scan, or with magnetic resonance imaging (MRI).

An example of a polyp on colonoscopy versus virtual colonoscopy.

Procedure

While preparations for VC vary, the patient will usually be asked to take laxatives or other oral agents at home the day before the procedure to clear stool from the colon. A suppository is also used to cleanse the rectum of any remaining fecal matter.

VC takes place in the radiology department of a hospital or medical center. The examination takes about 10 minutes and does not require sedatives. During the procedure,

* The patient is placed in a supine position on the examination table
* A thin tube is inserted into the rectum, so that air can be pumped through the tube in order to inflate the colon for better viewing.
* The table moves through the scanner to produce a series of two-dimensional cross-sections along the length of the colon. A computer program puts these images together to create a three-dimensional picture that can be viewed on the video screen.
* The patient is asked to hold his/her breath during the scan to avoid distortion on the images.
* The scanning procedure is then repeated in a reverse position.

After the examination, the information from the scanner must be processed to create the computer picture or image. A radiologist evaluates the results to identify any abnormalities.

The patient may resume normal activity after the procedure, but if abnormalities are found and the patient needs conventional colonoscopy, it may be performed the same day.

Advantages

VC is more comfortable than conventional colonoscopy for some people because it does not use a colonoscope. As a result, no sedation is needed, and the patient can return to his/her usual activities or go home after the procedure without the aid of another person. VC provides clearer, more detailed images than a conventional x-ray using a barium enema, sometimes called a lower gastrointestinal (GI) series. It also takes less time than either a conventional colonoscopy or a lower GI series.

Disadvantages

According to a recent article on Eurekalert.org, the main disadvantage to VC is cost. Another disadvantage is that a radiologist cannot take tissue samples (biopsy) or remove polyps during VC, so a conventional colonoscopy must be performed if abnormalities are found. Also, VC does not show as much detail as a conventional colonoscopy, so polyps smaller than 2 millimeters in diameter may not show up on the images. Furthermore Virtual Colonoscopy performed with CT exposes the patient to ionizing radiation, however some research has demonstrated that ultra-low dose VC can be just as effective in demonstrating colon and bowel disease due to the great difference in x-ray absorption between air and the tissue comprising the inner wall of the colon.