WHAT IS IT?
A noninvasive test that provides an inside look at the large intestine (colon).
PURPOSE
CT colonography allows radiologists to screen for polyps (lesions) in the colon that develop within the lining of the large intestine. Polyps are dangerous because they can turn into cancers, so early detection and removal is essential.
HOW IT WORKS
As the examination table slides into and out of a tunnel, it relays data to a computer system that creates two-dimensional cross-sectional images of your body. Those cross-sections are combined to generate a three-dimensional model of the abdomen, allowing the radiologist to literally take a trip through the colon (why it’s called virtual colonoscopy).
WHAT TO EXPECT
You may be given a gown to wear during the procedure. You will lie on a narrow examination table (first on your back, then on your side or stomach). Straps and pillows may be used to help you maintain the correct position and to hold still during the exam.
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. Sometimes a retention balloon is inflated on the rectal tube to help keep the tube positioned correctly. The purpose of the gas is to distend the colon as much as possible to eliminate any folds or wrinkles that might obscure polyps from the physician’s view.
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 five percent of patients. A muscle-relaxing drug may be injected intravenously or subcutaneously to lessen discomfort, but this is seldom necessary. The scanning procedure itself causes no pain or other symptoms.
When you enter the CT scanner, special lights may be used to ensure that you are properly positioned. With modern CT scanners, you will hear only slight buzzing, clicking and whirring sounds as the CT scanner revolves around you during the imaging process.You 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. The entire examination is usually completed within 15 minutes.
A physician, usually a radiologist, will analyze the images and send a signed report to your primary care physician or the physician who referred you for the exam, who will discuss the results with you. After most CT exams, you can return to your normal activities.
HOW TO PREPARE
Wear comfortable, loose-fitting clothing to your exam. Inform your doctor if you have heart, liver or kidney disease and if you could be pregnant.
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.
It is very important to clean out your colon 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 liquid that help empty the contents of the intestine.
