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
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:
A virtual colonoscopy may be done
Virtual colonoscopy is not commonly done for other
conditions at this time but may prove to be useful to:
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
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.
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
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
Virtual colonoscopy has advantages and disadvantages
compared to a regular 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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CitationsEinstein AJ, et al. (2007). Estimating risk of cancer associated with radiation exposure from 64-slice computed tomography coronary angiography. JAMA, 298(3): 317–323.Other Works ConsultedCotton PB, et al. (2004). Computed tomographic colonography (virtual colonoscopy): A multicenter comparison with standard colonoscopy for detection of colorectal neoplasia. JAMA, 291(14): 1713–1719.Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.Gupta S, et al. (2008). Variation of agreement in polyp size measurement between computed tomographic colonography and pathology assessment: Clinical implications. Clinical Gastroenterology and Hepatology, 6(2): 220–227.Kim DH, et al. (2007). CT colonography versus colonoscopy for the detection of advanced neoplasia. New England Journal of Medicine, 357(14): 1403–1412.Levin B, et al. (2008). Screening and surveillance for the early detection of colorectal cancer and adenomatous polyps, 2008: A joint guideline from the American Cancer Society, the U.S. Multi-Society Task Force on Colorectal Cancer, and the American College of Radiology. CA: A Cancer Journal for Clinicians, 58(3): 130–160.Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.
December 7, 2011
Adam Husney, MD - Family Medicine & Arvydas D. Vanagunas, MD - Gastroenterology
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