CT Colonography

Colorectal Cancer Basics 

  • Colorectal cancer is the second-leading cause of cancer deaths in the U.S.
  • Men and women are at equal risk of developing colorectal cancer.
  • African Americans and Native Americans have the highest rate of colon cancer and death from colon cancer of all groups in the U.S.
  • Early detection of colorectal cancer leads to easier treatments and higher survival rates.
  • More than one-third of colorectal cancer deaths could be avoided if all eligible individuals participated in regular screening.
  • Colorectal cancer screening is safe and effective.

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 What is Computed Tomographic (CT) Colonography?

CT colonography is a procedure used for the screening of colorectal cancer. The test involves an examination of your colon and rectum using pictures obtained using a CT (cat) scanner.


Just like a traditional colonoscopy, you will need to take a preparation to cleanse your colon, such as laxatives and/or enemas, prior to the test. Your doctor will prescribe a special diet, often clear liquids, for the day prior to your examination.


At the beginning of the test, a small flexible tube will be inserted into your rectum to introduce gas into your colon. A computer is used to combine the pictures creating both 2- and 3-dimensional views that allow a specially trained physician to view the images of your colon and rectum, similar to how they read typical CT scans of the abdomen or pelvis for example. They will review the images to look for polyps and potential cancer. The scanning procedure does not require sedation. If a polyp or other abnormality is discovered during the CT colonography, you will likely require a colonoscopy to biopsy or remove the abnormality. In some settings you will be able to have the colonoscopy on the same day. This will prevent you from having to repeat the colonic preparation requirements and miss another day out of your daily schedule.


A CT colonography can be performed in an outpatient imaging center, an outpatient office or a hospital setting.

When to Have This Test

Current recommendations indicate that the test should be performed once every five years for average risk individuals and who do not have any signs or symptoms. It is recommended that patients at higher risk for colorectal cancer, including those with a family history or a personal history of polyps or colon cancer should talk to their gastroenterologist about scheduling a colonoscopy since patients with these features are more likely have colon polyps that will require a colonoscopy to remove them.

 What is a Colonoscopy?

Colonoscopy is a procedure used in the screening and prevention of colorectal cancer. It is the test that most physicians, including gastroenterologists, recommend as the single best screening exam for colorectal cancer. It is the only method that combines both screening and prevention, because the doctor can remove pre-cancerous polyps during the procedure.


Your doctor will prescribe a diet, often clear liquids, for the day prior to your examination. Laxatives and/or enemas will be required. For more information, read the AGA Institute brochure on Preparing for a Colonoscopy.


The procedure involves the examination of the colon by use of a long, flexible, lighted tube — called a colonoscope — through which the doctor can view the entire colon and rectum for polyps or cancer, and if necessary, can remove pre-cancerous polyps during the same exam. If a polyp is found, it can be removed through a variety of methods with tools that are passed through the colonoscope.

Colonoscopy requires patients to be sedated and may take approximately 30 to 40 minutes. Some pressure may be felt from movement of the instrument during the exam and there may be some cramping afterwards. These symptoms are usually temporary and resolve quickly.


A colonoscopy can be performed safely in an ambulatory surgical center (ASC), an outpatient office or a hospital setting. Patients do not have to be hospitalized, unless other conditions exist that would require a hospital stay.

When to have this test

Recommended every 10 years after age 50 for average-risk individuals. Patients at higher risk for colorectal cancer, including those with a family history, or with a personal history of polyps or other diseases, should talk to their gastroenterologist about appropriate screening intervals.

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Other Screening Tests

There are a number of other screening tests for colorectal cancer, including:

  • Fecal immunohistochemical test (FIT)
  • Fecal occult blood test (FOBT)
  • Flexible sigmoidoscopy

Talk to your gastroenterologist to make an informed decision about which screening test(s) are right for you. Read more about colorectal cancer and screening tests.

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Questions to Ask Your Doctor: Is CT Colonography Right for You? 

  • What are my risk factors for colorectal cancer?
  • What are my CRC screening options given my history?
  • What are the risks and benefits of a standard colonoscopy?
  • What are the risks and benefits of a CT colonography exam?
  • What is the risk of radiation from CT colonography?
  • What happens if a polyp is found as a result of the CT colonography exam?
  • If a polyp is found, can I have a standard colonoscopy in the same day or do I have to come back?
  • If I have to come back, will I need to repeat the colonic preparation?
  • How do I prepare for a colonoscopy or CT colonography exam?
  • What can I eat/drink during the colonic preparation period?
  • Can CT colonography detect other parts of the body?
  • How often should I have a CT colonography if my colon is clear?
  • If a polyp is found, will I have a repeat CT Colonography exam or will I need a colonoscopy?
  • How often do you perform CT colonography?
  • How many CT colonographies have your performed?
  • How often do CT colonography exams result in the need for a standard colonoscopy?
  • What is your policy/philosophy on leaving small polyps for surveillance?
  • Do you report all findings?
  • Do you read the CT colonography yourself?

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Adapted from Levin B., Lieberman DA., McFarland B. et al. Screening and Surveillance for the Early Detection of Colorectal Cancer and Adenomatous Polyps, 2008: A Joint Guideline From the American Cancer Society, the US Multi-Society Task Force on Colorectal Cancer, and the American College of Radiology. Gastroenterology. 2008 May;134(5):1570-95.

Date reviewed: April 2013