Virtual Colonoscopy

What is CT Colonography?

CT imaging uses special x-ray equipment to produce multiple images or pictures of the inside of the body and a computer to join them together in cross-sectional views of the area being studied. The images can then be examined on a computer monitor or printed.

CT colonography uses CT scanning to obtain an interior view of the colon (the large intestine) that is ordinarily only seen with an endoscope inserted into the rectum.

What are some common uses of the procedure?

The major reason for performing CT colonography is to screen for polyps and other lesions in the large intestine.

The goal of screening with colonography is to find these growths in their early stages, so that they can be removed before cancer has had a chance to develop. Most physicians agree that everyone older than 50 years should be screened for polyps every seven to 10 years. Individuals at increased risk should be screened every five years. Risk factors for the disease include a history of polyps, a family history of colon cancer, or the presence of blood in the stool.

How should I prepare for the procedure?

You should wear comfortable, loose-fitting clothing to your exam. You may be given a gown to wear during the procedure.

Metal objects including jewelry, eyeglasses, dentures and hairpins may affect the CT images and should be left at home or removed prior to your exam. You may also be asked to remove hearing aids and removable dental work.

It is very important to clean out your bowel the night before your CT colonography examination so that the radiologist can clearly see any polyps that might be present. You will be asked to take either a set of pills or a cathartic liquid. Some common preparations are the Fleet Prep Kit 1. Be sure to inform your physician if you have heart, liver or kidney disease to be certain that the bowel prep will be safe. On the day before your exam, you should limit your food intake to clear liquids such as broth, tea or juice. You will be able to resume your usual diet immediately after the exam.

How does the procedure work?

Modern CT scanners are so fast that they can scan through large sections of the body in just a few seconds. Such speed is beneficial for all patients but especially children, the elderly and critically ill.

For CT colonography, the computer generates a detailed three-dimensional model of the abdomen and pelvis, which the radiologist uses to view the bowel in a way that simulates traveling down the colon. This is why it is often called a virtual colonoscopy.

How is the procedure performed?

The technologist begins by positioning you on the CT examination table, usually lying flat on your back or possibly on your side or on your stomach.

A very small, flexible tube will be passed two inches into your rectum to allow air to be gently pumped into the colon using a hand-held squeeze bulb. Sometimes an electronic pump is used to deliver carbon dioxide gas into the colon. In either case, you will be able to control the amount of air or gas passing into the colon. The purpose of the gas is to distend the colon a little to eliminate any folds or wrinkles that might obscure polyps from the physician’s view.

Next, the table will move through the scanner. Patients are asked to hold their breath for about 15 seconds before turning over and lying on their back for a second pass is made through the scanner. In some centers the sequence of positions may be the opposite: facing upward first and then facing down. Once the scan is done, the tube is removed.

The entire examination is usually completed within 15 minutes.

What will I experience during the procedure?

The vast majority of patients who have CT colonography report a feeling of fullness when the colon is inflated during the exam, as if they need to pass gas. Significant pain is uncommon, occurring in fewer than 5 percent of patients. A muscle-relaxing drug may be injected intravenously to lessen discomfort, but this is seldom necessaryYou will be alone in the exam room during the CT scan, however, the technologist will be able to see, hear and speak with you at all times. After a CT exam, you can return to your normal activities.

What are the benefits vs. risks?

Benefits

 CT colonography has a markedly lower risk of perforating the colon than conventional colonoscopy. Most of those examined do not have polyps, and can be spared having to undergo a full colonoscopy.

 Elderly patients, especially those who are frail or ill, will tolerate CT colonography better