What is a virtual colonoscopy?
A virtual colonoscopy uses X-rays and computers (computed tomography [CT] or magnetic resonance imaging [MRI]) to take two- or three-dimensional images of the interior lining of your large intestine (colon) and rectum. A virtual colonoscopy can be used to screen for precancerous and cancerous growths in the colon or rectum (colorectal cancer), such as polyps or tumors.
Virtual colonoscopy (also called computed tomographic colonography, or CTC) is still being studied to determine whether the results are as accurate as a regular colonoscopy. Virtual colonoscopy is not yet widely available.
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, your preference, and your doctor. Talk to your doctor about what puts you at risk and what test is best for you.
For more information on screening tests for colon cancer, see:
Why is it done?
A virtual colonoscopy may be done to:
Virtual colonoscopy is not commonly done for other conditions at this time but may prove to be useful to:
How do I prepare for it?
Virtual colonoscopy requires the same cleansing colon prep as a regular colonoscopy. Colon prep takes 1 to 2 days depending on which type of prep your doctor recommends. For many people, the prep for a colonoscopy is more trying than the actual test. Researchers are studying methods that could be used to mark (tag) stool in the colon before virtual colonoscopy so cleansing colon preps would not be needed.
Before this test, you will need to clean out your colon. The following information gives you a general idea of the preparation for a colonoscopy. Your doctor will give you specific instructions before your test.
How is it done?
Virtual colonoscopy may be done in a doctor's office, clinic, or a hospital. 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 will be given a gown to wear during the test.
First, you will be asked to lie on your back. Air (or in some cases, carbon dioxide) will be used to expand your colon. This helps the doctor see all parts of your colon. The air is added using a tube placed in your anus. It may be uncomfortable when the air is put into your colon. You may be given medicine to help the muscles in your colon relax.
You will be asked to hold your breath while the pictures of your colon are being taken. If you can't hold your breath for the whole time, the doctor may need to take pictures a couple times in order to get the whole colon. You may be asked to roll over and lie on your stomach. The doctor will ask you to hold your breath again and pictures will be taken with you lying in this position.
The test usually takes about 15 to 30 minutes.
How does a virtual colonoscopy differ from a regular colonoscopy?
Virtual colonoscopy has advantages and disadvantages compared to a regular colonoscopy.
What do I need to consider about a virtual colonoscopy?
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. Since your colon is already clean, you may have the regular colonoscopy the same day.
Virtual colonoscopy is not available everywhere because it requires special equipment and special training to interpret the test. The initial evaluations on virtual colonoscopy were done by highly trained radiologists, so the results of your virtual colonoscopy may vary widely depending on the amount of experience your doctor's office or clinic has with the procedure.
Virtual colonoscopy is being studied to determine whether the results are as accurate (sensitivity) as a regular colonoscopy. More evidence is needed to show that virtual colonoscopy is a benefit in people with average risk for colon cancer and whether this screening method can prevent cancer. Colon preps that are more comfortable are also being studied.
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