CT Colonography - Information for Patients

  • What is CT Colonography?
  • What are the benefits?
  • What are the risks?
  • Preparation
  • How is the procedure performed?

What is CT Colonography?

(Video- click the play button to begin)

CT Colonography is a screening test for colorectal cancer. It is method to detect tumours and precancerous lesions (polyps) in the colon. CT colonography provides an interior view of the colon (the large intestine) that is otherwise only seen with a more invasive procedure where an endoscope is inserted into the rectum.

A Radiologist, a physician with advanced specialist training in medical imaging, then uses special computer software to examine the images for polyps.







Benefits of CT Colonography

CT colonography has several benefits over a conventional colonoscopy:

  • This minimally invasive test provides three-dimensional images that can depict many polyps and other lesions clearly.
  • CT colonography has a lower risk of perforating the colon than conventional colonoscopy. Most of those examined do not have polyps, and can be spared having to undergo a full colonoscopy.
  • CT colonography is an excellent alternative for patients who have clinical factors that increase the risk of complications from colonoscopy, such as treatment with a blood thinner or a severe breathing problem.
  • Elderly patients, especially those who are frail or ill, will tolerate CT colonography better than conventional colonoscopy.
  • CT colonography can be helpful when colonoscopy cannot be completed because the bowel is narrowed or obstructed for any reason, such as by a large tumour or diverticulosis.
  • If conventional colonoscopy cannot reach the full length of the colon—which occurs up to 10 percent of the time—CT colonography can be performed on the same day because the colon has already been cleansed.
  • CT colonography provides clearer and more detailed images than does a conventional barium enema x-ray examination.
  • CT colonography is tolerated well. Sedation and pain-relievers are not needed, so there is no recovery period.
  • CT colonography is less costly than colonoscopy.
  • No radiation remains in a patient's body after a CT examination.
  • X-rays used in CT scans usually have no side effects.



What are the risks of CT Colonography?

There is a very small risk that inflating the colon with air could injure or perforate the bowel. This has been estimated to happen in less than one in 2,000 patients.

There is always a slight risk associated with exposure to radiation. However, the benefit of an accurate diagnosis far outweighs the risk. For more information on the risks associated with X-rays you can download the information sheet below:

X-rays- how safe are they?

Download now

Women should always inform their physician and CT radiographer if there is any possibility that they are pregnant.






What preparation is necessary?

You should wear comfortable, loose-fitting clothing to your exam. You may be given a gown to wear during the procedure.

Women should always inform their physician and the CT technologist if there is any possibility that they are pregnant.

It is very important to clean out your bowel the night before your CT colonography examination so that the radiologist can clearly see any polyps that might be present. You will be asked to take either a set of pills or a cathartic liquid.

Be sure to inform your physician if you have heart, liver or kidney disease to be certain that the bowel prep will be safe. On the day before your exam, you should limit your food intake to clear liquids such as broth, tea or juice. You will be able to resume your usual diet immediately after the exam.




How is the procedure performed?

The Radiologist begins by positioning you on the CT examination table, usually lying on your side. A small, flexible tube will be passed into your rectum to allow air to be gently pumped into the colon using a hand-held squeeze bulb. The purpose of the gas is to distend the colon as much as possible to eliminate any folds or wrinkles that might obscure polyps from the physician’s view. Some radiologists will give you a small injection that helps prevent the colon going into spasm. This has the advantage of making the images easier for the radiologist to read and will make the procedure more comfortable.

The sequence of positions may be facing upward first. Patients are asked to hold their breath for about 15 seconds before turning over for a second pass is made through the scanner.

Once the scan is done, the tube is removed.

The entire examination is usually completed within 15 minutes