Virtual colonoscopy is a procedure used to look for signs of pre-cancerous growths called polyps, cancer; and other diseases of the large intestine. Images of the large intestine are taken using computerized tomography (CT) or, less often, magnetic resonance imaging (MRI). A computer puts the images together to create an animated, three-dimensional view of the inside of the large intestine.
What is computerized tomography (CT)?
CT is a procedure that takes hundreds of cross-sectional X-rays in a few seconds. Like putting together a loaf of bread from its many slices, a computer puts cross-sectional X-ray pictures together to form whole images of internal organs.
How to Prepare for Virtual Colonoscopy
The radiologist will provide instructions about how to prepare for virtual colonoscopy. The process is called bowel prep. The bowel prep for virtual colonoscopy is almost identical to the bowel prep for conventional colonoscopy. Generally, all solids must be emptied from the gastrointestinal (GI) tract by following a clear liquid diet for 1 to 3 days before the procedure. Acceptable liquids include:
- Fat-free bouillon or broth
- Strained fruit juice
- Water
- Plain coffee
- Plain tea
- Sports drinks, such as Gatorade
- Gelatin
A laxative will be required the night before virtual colonoscopy. A laxative is medicine that loosens stool and increases bowel movements. Laxatives are usually swallowed in pill form or as a powder dissolved in water. After the bowel prep, patients undergoing CT drink a liquid called contrast media that causes the large intestine to appear very bright during CT. Contrast media helps the doctor identify abnormal tissues.
How is virtual colonoscopy performed?
Virtual colonoscopy is performed wherever the CT scanner or MRI unit is located - usually in the radiology department of a hospital or medical center. The procedure takes about 10 minutes and does not require sedation.
- Patients will lie face up on a table.
- A thin tube will be inserted through the anus and into the rectum.
- For CT, carbon dioxide gas will be pumped through the tube to expand the large intestine for better viewing.
- For MRI, contrast media will be given rectally to expand the large intestine.
- The table will move through the CT scanner or MRI unit to produce a series of cross-sectional images of the colon.
- At various points during the procedure, the doctor may ask patients to hold their breath to steady the images.
- The procedure will be repeated while patients lie face down.
After the procedure, cross-sectional images taken by CT or MRI are processed to create three-dimensional, computer-generated images of the large intestine. A radiologist evaluates the results to identify any abnormalities. If abnormalities are found, conventional colonoscopy may be performed at a later time.
How is virtual colonoscopy different from conventional colonoscopy?
The main difference between virtual and conventional colonoscopy is how the doctor sees inside the colon. Conventional colonoscopy uses a long, lighted, flexible tube called a colonoscope to view the inside of the colon, whereas virtual colonoscopy uses CT or MRI.
What are the advantages of virtual colonoscopy?
- Virtual colonoscopy has several advantages over other procedures:
- Virtual colonoscopy takes less time than a conventional colonoscopy.
- Virtual colonoscopy can see inside a colon that is narrowed due to inflammation or the presence of an abnormal growth.
What are the disadvantages of virtual colonoscopy?
- Virtual colonoscopy has several disadvantages:
- As with conventional colonoscopy, virtual colonoscopy requires bowel prep and the insertion of a tube into the rectum for expanding the large intestine with gas or liquid.
- Virtual colonoscopy does not allow the doctor to remove tissue samples or polyps.
- Virtual colonoscopy does not detect pre-cancerous polyps smaller than 10 millimeters.
- No sedation is needed. A patient can return to usual activities or go home after the procedure without the aid of another person.
- Many health insurance plans do not pay for virtual colonoscopy cancer screening.
- Virtual colonoscopy is a newer technology and is not as widely available.
Points to Remember
- Virtual colonoscopy is a procedure used to look for signs of pre-cancerous growths, called polyps; cancer; and other diseases of the l large intestine.
- All solids must be emptied from the gastrointestinal (GI) tract by following a clear liquid diet for 1 to 3 days before virtual colonoscopy.
- Virtual colonoscopy does not require insertion of a colonoscope or sedation.
- During virtual colonoscopy, a tube is inserted into the rectum to expand the large intestine with gas or liquid.
- Virtual colonoscopy does not allow the doctor to remove tissue samples or polyps.