A virtual colonoscopy uses computed tomography (CT) or magnetic resonance imaging (MRI) to make a three-dimensional image of the inner lining of the large intestine (colon) and rectum. It can be used to screen for precancerous and cancerous growths in the colon or rectum (colorectal cancer), such as polyps or tumors.
Virtual colonoscopy is one of many tests that may be used to screen for colon cancer. Which screening test you choose depends on your risk and what you prefer. Talk to your doctor about what puts you at risk and what test is best for you.
How is it different from a regular colonoscopy?
Virtual colonoscopy has advantages and disadvantages compared to a regular colonoscopy.
- Virtual colonoscopy is less invasive and safer, and it takes less time than a regular colonoscopy.
- A thin tube to insert air into the colon is placed in the rectum rather than a long flexible tube that is moved up your colon.
- No medicine to relax or sedate you is needed. So you will be able to drive yourself home and resume normal activities.
- Virtual colonoscopy can show the inside of a colon that is narrow due to inflammation or an abnormal growth.
- Virtual colonoscopy may not show polyps smaller than 10 mm (0.4 in.).
- Virtual colonoscopy isn't covered by all health insurance plans. Check with your insurance plan before you have the test.
- If a polyp is found, you'll need a regular colonoscopy to confirm the diagnosis and remove the polyp so it can be looked at under a microscope.
Why It is Done
A virtual colonoscopy may be done to:
- Screen for colorectal cancer or polyps.
- Monitor the growth of polyps.
- Screen for recurrence of colorectal cancer in people who have had surgery for this disease.
- Replace a regular colonoscopy if the thin lighted scope can't be inserted in the colon for some reason. For instance, it may be done when a tumor blocks the passage.
Is it right for you?
If you have an average risk for colorectal cancer, virtual colonoscopy may be an appropriate screening test for you. But if you are at an increased risk, you may require a regular colonoscopy because tissue biopsies or polyp removal can be done at the same time.
Virtual colonoscopy requires the same cleansing colon prep as a regular colonoscopy. If an abnormality is found on virtual colonoscopy, you may need a regular colonoscopy to remove and test the abnormal tissue.
How to Prepare
Virtual colonoscopy requires the same cleansing colon prep as a regular colonoscopy.
If you are having virtual colonoscopy using CT, you will be given some liquid to drink after your bowel prep. This drink is a contrast medium. It makes the large intestine easier to see in the pictures.
- Follow your doctor's directions about when to stop eating solid foods and drink only clear liquids. You can drink water, clear juices, clear broths, flavored ice pops, and gelatin (such as Jell-O).
- Drink the "colon prep" liquid as your doctor tells you. You will want to stay home, because the liquid will make you go to the bathroom a lot. Your stools will be loose and watery. It's very important to drink all of the liquid. If you have problems drinking it, call your doctor.
- Do not eat any solid foods after you drink the colon prep.
- Stop drinking clear liquids for a few hours before the test. Your doctor will tell you how many hours this will be.
How It Is Done
Virtual colonoscopy is usually done in the radiology department at a hospital or medical center. The test is most often done by a doctor who specializes in performing and interpreting diagnostic imaging tests (radiologist). The doctor may also have an assistant.
You will need to take off most of your clothes. You'll get a gown to wear during the test.
First, you will be asked to lie on your back on the table of the CT or MRI machine. A thin tube is put into your rectum through your anus. For CT, air or carbon dioxide gas will be pumped through the tube. (There may be some discomfort as the gas expands your colon.) For MRI, a contrast liquid will be given through the tube into the colon. This helps the doctor see all parts of your colon.
The table will slide into the CT or MRI machine so pictures of your colon can be taken. You may be asked to hold your breath when pictures are taken. This can help prevent blurry pictures. Then the procedure will be repeated while you lie facedown.
A negative result means that your colon appears normal. A positive result means that abnormal tissue, like a polyp, was seen. With a positive result, you'll need a colonoscopy to remove the polyp or take a tissue sample. Also, if the images show a possible problem outside the colon, you'll need more tests.