CT colonography is a minimally invasive colorectal cancer screening test sometimes referred to as a virtual colonoscopy because it uses 2-D and 3-D imaging.
Using a CT scanner, certified radiologists take images of your colon that appear on a computer screen. The images recreate the colon and reveal polyps as small as 1 centimeter with 90 to 95 percent accuracy.
The CT colonography is an alternative to a colonoscopy for people who: - Had an incomplete colonoscopy. - A tortuous colon — one that’s longer than normal, resulting in a lot of loops. - On blood thinners or anti-coagulants because of heart issues. Doctors also prescribe the test for frail elderly people and those with breathing problems.
On the positive side, the test:
- Requires no sedation
- Is a quick examination, usually 15 to 20 minutes
- Is a well-tolerated alternative to colonoscopy
- Detects polyps 10 millimeters or larger with 90 percent accuracy
- Detects polyps 6 to 9 millimeters with 70 to 80 percent accuracy
- Reveals the inside of the colon as well as the outside
- Detects other problems, including aneurysms and early-stage malignancies
- Has no immediate side effects
On the negative side, the test:
- Requires a bowel prep for a clean colon
- May not detect all small polyps and cancers
- Could injure or perforate the bowel when it’s inflated with carbon dioxide (This has been estimated to happen in fewer than one in 10,000 patients.)
- Has a slight chance of cancer resulting from exposure to radiation, but the benefit of an accurate diagnosis generally outweighs the risk. The dose of radiation is much less than is used for a diagnostic CT scan
- May not be used for women who are pregnant. If you are pregnant, you should not get any kind of CT scan, including CT colonography
- May require a colonoscopy to remove any polyps that are found
- Is recommended every five years
How is the test administered?
CT colonography requires a clean colon, so you need to take a liquid laxative a day before the test. You also may need to drink a creamy barium liquid before the test to help the radiologist identify any stool remaining in the colon.
For the test, the radiologist inserts a small tube in your rectum to inflate the colon with carbon dioxide. This enlarges the colon so that the CT scan can generate clear, detailed images that the radiologist can enlarge and rotate.
When you get a CT colonography, you lie on your back for one portion of the test and on your stomach for the other. No radiation remains in your body after the CT examination.
In cases when a conventional colonoscopy cannot reach the full length of the colon, which occurs as much as 10 percent of the time, CT colonography can be performed on the same day because the colon has already been cleansed.
Test results for a CT colonography
Your doctor will talk with you about your test results. If polyps are found, you may need a traditional colonoscopy to determine whether they’re cancerous. If they are, your doctor will talk with you about treatment options.
If the results are negative, your doctor may recommend another CT colonography in five years.