Discusses virtual colonoscopy (computed tomographic colonography). Covers why and how it is done. Explains how it differs from a regular colonoscopy. Covers things to think about when choosing virtual colonoscopy.
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:
Screen for recurrence of colorectal cancer in people who have
had surgery for this disease.
Evaluate abnormal results from other
Replace a regular colonoscopy if the thin lighted
scope cannot be inserted in the colon for some reason, such as when a tumor
blocks the passage.
Virtual colonoscopy is not commonly done for other
conditions at this time but may prove to be useful to:
Detect other problems or diseases of the
anus, rectum, or large intestine (colon).
Check the source of
Check the cause of chronic
Monitor the treatment of inflammatory bowel
How do I prepare for it?
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.
One to two days before a colonoscopy, you will stop eating solid
foods and drink only clear fluids, such as water, tea, coffee, clear juices,
clear broths, Popsicles, and gelatin (such as Jell-O).
Your doctor will recommend a medicine for you to use to prepare for your colonoscopy. It will most likely be a prescription
laxative tablet and/or a laxative solution (such as Nulytely or Golytely) that you drink before your colonoscopy. This solution will be given to you as a powder
that you will mix with
1 gal (3.8 L) of water. You may need to drink this laxative solution over 1 to 2 hours in the evening before the test. Or you may be asked to drink half the solution the evening before your test and the other half the morning of your test. This solution
may taste very salty and may make you feel sick to your stomach. To make your
colon prep easier, you may want to try some of the following tips:
You may find it easier to drink the solution if you use a straw with the end at the back of your throat (to bypass the taste buds).
Each time you drink some of the solution,
you may also drink some water or clear fluids (like apple juice) to help get
rid of the salty taste in your mouth.
You may find it easier to
drink the solution if you chill it in the refrigerator first.
your doctor if it is okay for you to add flavored drink crystals (such as
Crystal Light) to the solution.
Add lemon juice to the solution or
suck on sliced lemon wedges after you take a drink.
Your doctor may recommend a different preparation product, such as the
Nutraprep meal kit or sodium phosphate tablets (for example, Visicol). These are other methods
of preparing for a colonoscopy. If you are concerned about the bowel prep, you can ask your doctor whether another method will
work for you.
Oral sodium phosphate (either tablets or liquid) can cause kidney problems. Make sure you check with your doctor before using a nonprescription sodium phosphate product.
You will want to stay home while doing the colon prep because it will make you use the bathroom
Drink plenty of clear fluids during the prep so you will not
dehydrated. This will also help clean out your colon
completely after you finish the colon prep.
Do not eat any solid
foods after doing the colon prep.
Stop drinking clear
liquids 6 to 8 hours before the test.
Your doctor may have
you use an enema 30 to 60 minutes before the test to completely clean out your
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
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
How does a virtual colonoscopy differ from a regular colonoscopy?
Virtual colonoscopy has advantages and disadvantages
compared to a regular colonoscopy.
Virtual colonoscopy is less invasive, safer,
and 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. (But there is usually some discomfort
when the air is inserted.)
No medicine to relax or sedate you is
needed, so you will be able to drive yourself home and resume normal
Virtual colonoscopy may not show polyps
smaller than 10 mm (0.4 in.).
You will need to hold your breath for short periods
of time while the computed tomography (CT) scanner takes pictures of your
colon. CT scanning will need to be done twice: once while you lie on your back
and then again while you lie on your stomach.
is not covered by all health insurance plans. Check with your insurance plan
before having the test.
There is a small chance of developing
cancer from having some types of CT
scans.1 If you are concerned about this risk, talk to your doctor
about the amount of radiation this test may give you or your child and confirm
that the test is needed.
If a polyp is found, regular colonoscopy will be needed
to confirm the diagnosis and remove the polyp so it can be looked at under a
microscope. You will
need to do another bowel preparation before the 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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Einstein AJ, et al. (2007). Estimating risk of cancer
associated with radiation exposure from 64-slice computed tomography coronary
angiography. JAMA, 298(3): 317–323.
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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
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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):
Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.
How this information was developed to help you make better health decisions.