Virtual colonoscopy

Computerized tomography (CT) colonography — sometimes called virtual colonoscopy — uses a CT scanner to produce hundreds of cross-sectional images of your abdominal organs. Those images are combined and digitally manipulated to provide a detailed view of the interior of your colon without having to insert a colonoscope or use sedation.

Many doctors and medical organizations still consider virtual colonoscopy to be experimental. Others use virtual colonoscopy when conventional colonoscopy or other screening exams can't be done.

How do you prepare?

As with conventional colonoscopy, the success of the exam depends largely on how well you clear your colon. Clearing your colon for a virtual colonoscopy requires a restricted diet and laxatives, just as with the conventional version of the exam.

Members of your health care team will give you instructions on cleansing your colon. Preparation for your virtual colonoscopy may require you to:

• Stop taking certain medications a week or two before the exam. Certain medications may interfere with the virtual colonoscopy, so your doctor may ask you to stop taking certain medications in the days or hours before your exam.
• Avoid high-fiber food for up to three days before your procedure. Examples of high-fiber foods include lettuce, celery, corn, beans, apple skin and citrus pulp.
• Begin a clear-liquid-only diet the day before the exam. Examples of allowable liquids may include water, decaffeinated coffee without cream, decaffeinated tea, clear sodas, chicken broth and apple juice.
• Drink a colon-cleansing solution the evening before your exam. The laxative drink will cause you to have to use the toilet several times over the course of a few hours. The colon-cleansing solution can also cause temporary bloating, nausea, diarrhea and stomach cramps.
• Take a prescription medication to identify stool in your colon. During the exam, the stool-tagging medication will help doctors determine whether a colon abnormality is remaining stool or a polyp.
• Stop drinking any liquids a few hours before your exam.

In rare instances, phosphate-based colon-cleansing solutions have caused kidney damage in certain groups of people. These groups include healthy older adults, those taking medication for hypertension, arteriosclerosis or heart disease, and those with chronic kidney disease. You may be given a different type of solution if you fit in one of these categories.

How is it done?

On the day of your virtual colonoscopy, you'll be asked to change into a gown and to try to have a bowel movement one last time. In some cases, you'll receive an injection of medication to reduce the chance that you'll experience stomach cramps during the procedure.

To help in making the images, your health care team fills your colon with air or carbon dioxide. During this part of the procedure, you lie on your side and a small catheter is inserted inside your rectum. The air or gas fills your colon, which can cause a feeling of pressure in your abdomen.

Then you'll move to lie on your back, and the table you rest on is moved into the CT scanner. Your body is moved through the scanner. You will then be asked to turn over to your stomach or your side and go through the scanner again. Other positions may be necessary to obtain the best images. You'll be asked to hold your breath for several seconds to limit abdominal movement and avoid distorting the images.

In rare instances, you may receive a contrast agent through a vein in your arm (intravenously) in order to help the radiologist obtain clearer images. There is a small risk of allergic reaction to the contrast agent, so tell the radiologist if you have any allergies.

Virtual colonoscopy is typically faster than traditional colonoscopy. A scan of your colon takes about 10 minutes. Expect the entire virtual colonoscopy procedure to take 20 to 30 minutes.

After the procedure

After your virtual colonoscopy, most of the air or gas is removed from your colon through the catheter in your rectum. You may feel bloated as the remaining gas dissipates over the course of the day. You may have gas pains, pass gas or have more frequent bowel movements.

If your signs and symptoms aren't getting better or if you're feeling worse, call your doctor.

You can begin eating your usual diet and taking your medications once your virtual colonoscopy exam is complete.

Results

After your exam, your doctor will discuss your results with you. Any further action you take depends on your particular situation.

• Negative results. A virtual colonoscopy that's negative means that no polyps or unusual areas were discovered during the exam. Discuss with your doctor what type of colon cancer screening you should undergo in the future. Because virtual colonoscopy is considered experimental, no firm guidelines exist to instruct doctors about the frequency of screening with this method.
• Positive results. A virtual colonoscopy that's positive means that growths or polyps were discovered on the images. Your doctor may recommend a conventional colonoscopy to obtain samples of the growths in question and to remove suspected polyps if they are larger than 5 to 10 millimeters (mm). In some cases, the conventional colonoscopy can be done the same day as your virtual colonoscopy. But you'll need to make arrangements to have someone drive you home after a conventional colonoscopy. If polyps smaller than 5 mm are found during virtual colonoscopy, your doctor may recommend follow-up screening in three to five years, depending on your risk factors and your preferences.

Ask your doctor if your virtual colonoscopy was a good-quality exam. If the colon wasn't completely empty of stool when examined, parts may have been obscured and abnormalities may not have been seen.