What is CT colonography?

Computerized tomographic (CT) colonography is a test used to check your colon for colorectal cancer and other health conditions in your gastrointestinal (GI) tract. It is sometimes called a virtual colonoscopy (but it is not the same thing as a standard colonoscopy).

This test will look at your colon and rectum using a special machine (CT scanner) to take pictures of the colon.

You do not need to be put to sleep for this test.

With CT colonography, your doctor can look at your colon from many different angles.

You will need to clean out your colon before the test, just like for a colonoscopy.

CT colonography

If a polyp is found during this test, you will need to have colonoscopy so it can be removed. A polyp is a mushroom-like growth on the inside wall of the colon or rectum.

CT colonography can be performed in many different settings, such as an outpatient office, X-ray center or hospital.

If CT colonography is used to test for colon cancer, it should be done every five years, if you are at normal risk.

CT colonography may done for these reasons:

  • General test to check for colorectal cancer.
  • To check the colon if a regular colonoscopy fails, typically because your doctor was not able to move the flexible tube all the way through the colon.
  • It may be used in certain situations to check the abdomen and colon in patients with belly pain or unexplained weight loss.

Preparing for CT colonography

Your doctor or nurse will review the steps with you and make sure that you know how to get ready and what you can expect during and after the test. If you have any questions, be sure to bring them up with the doctor or nurse.

Give your doctor a list of all the medications you are taking and any allergies you have.

  • The list should include both prescription and over-the-counter (OTC) drugs, like aspirin, NSAIDs or vitamins or supplements.
  • Ask your doctor before the test if any of your medications can be taken on the day of your CT colonography.
  • Ask your doctor before the test if any of your medications should not be taken before your CT colonography.
  • Ask your doctor before the test if you should take your medications the night before your CT colonography.

Tell your doctor if you:

  • Have diabetes and what medications you are on for it.
  • Are taking blood thinners or have bleeding or blood-clotting problems.
  • Have a pacemaker or other implanted electromedical devices.
  • Have had stomach or bowel surgery, swallowing problems or other gastrointestinal (GI) problems.
  • Have heart, lung or any other health problems that may need special care before the test.

A vital step

One vital step to get ready for CT colonography is to fully clean out the colon. For many, this step can be the hardest part of the procedure.

You need to do this step carefully and completely, because if your colon is not cleaned out enough, your doctor will not be able to do the exam. You should check with your health plan first to see if they will pay for this test.

There are important steps you must take to safely get ready for CT colonography. These are general instructions. Be sure to follow any instructions given to you by your doctor.

You will need a special diet, often clear liquids, for the day before your test. Your doctor will give you a list of what you are able to eat and drink for the days before the test.

Laxatives and/or enemas will be needed to clean out your colon. Your doctor will tell you which one to take and when you should use it.

On the day of the test, you will not be able to have any metal on you and will be asked to change into a hospital gown for the test.

CT colonography can be done in an outpatient or hospital setting. Be sure you know exactly where you need to go the day of your procedure, as it may not be the same as your doctor’s office. Be sure to ask your doctor or nurse if there is anything you do not understand.

During your CT colonography

Your doctor will tell you more specifically what you can expect during the test. Some things may include:

  • A nurse will review your medical history, medications and allergies.
  • You will change into a hospital gown.
  • Your doctor will review the consent form for the test, answer any of your questions and ask you to sign the form, which says you understand the test being done.
Patient and Doctor

What to expect

During the test, everything will be done to make sure that you are at ease, safe and comfortable.

You will not be put to sleep for this test.  This means that after the test, you will be able to go on about your regular activities.

To start, you will lay on your back while inside a computerized tomography (CT) machine.

A small, rubber tube will be gently and carefully placed into your rectum, passing through the anus. This may feel uncomfortable, but will not last long.

Air will be passed through the small, rubber tube to expand the bowels. You may feel the need to move your bowels or some cramping or fullness.

Next, you will lay on your stomach for the CT scanner to take more pictures.

You must stay as still as you can while the pictures are being taken so they come out clear.

A radiologist will look at the images to detect any signs of polyps, cancer or other health issues.

If a polyp or other abnormality is found, you will likely need a colonoscopy to remove it.

After CT colonography

Your doctor will tell you more specifically what you can expect after the test. Some things may include:

  • Since you will not be given medicine to make you feel sleepy, you should be able to go back to your normal routine after the test.
  • Your doctor or nurse will review the results with you and give you any other details or next steps you may need.
  • You may feel some minor issues, such as cramping or belly pain after the test. You may pass a lot of gas after the test. This is caused by the air moving around in your colon. These should go away in less than 24 hours.

Contact your doctor’s office if you have any questions after your CT colonography.


There are few risks with CT colonography, but be sure to talk to your doctor about risks specific to you.

You will be exposed to a small amount of radiation from the X-ray images.

You could have reactions to the medicines and preparation used to get you ready for the test, such as: upset stomach, throwing up, swelling of the belly, or rectal irritation.

If you are having pain after your CT colonography that doesn’t go away, call your doctor.