Computed Tomography Colonography (CTC)

Why do you perform these tests?

  • To look for suspected bowel cancer and test patients at increased risk of developing bowel cancer
  • For failed or incomplete conventional colonoscopies

Who will perform the test?

Our Consultant Radiologists Dr Tony Blakeborough and Dr James Hampton and specialised Radiographers will perform this diagnostic test.

How do I prepare for the test?

You will need to drink the Gastrografin liquid to prepare for the test. This is to help us see your colon and its contents clearly. A special diet is very important before the test (low residue) along with the bowel preparation (Gastrografin liquid). You will need to start the preparation the day before your appointment. Once you have taken the preparation, it is important to be close to a toilet as it often causes frequent loose bowel motions. If you take iron tablets, please stop taking these 4 days before your appointment.

Bowel preparation for CT Colonography

A special diet has been designed to prepare and cleanse your colon before the examination. It is important to follow this diet properly because too much faeces in your bowel can make it difficult for the doctor looking at the scan to interpret it.

Gastrografin Liquid (Bowel Preparation)

Although this liquid does have a slight laxative effect, it is designed to allow us to clearly see faeces in your colon. Do not be alarmed if you haven’t been to the toilet many times after drinking the liquid, your test can still be performed. Gastrografin is safe to drink. If you have had a severe allergic reaction to x-ray contrast in the past we may need to give you an alternative preparation. Please telephone us for further advice if you think you may have an allergy.

What happens during the test?

You will be asked to change into a hospital gown on arrival at the department in your own private changing area. A member of staff will put a needle (cannula) into a vein in your arm before you enter the scan room. This is so that a muscle relaxant (Buscopan) and x-ray contrast medium can be injected during the scan. We will ask you some questions and explain the procedure to you so you understand what is happening. You can also ask us questions at any time if you are unsure about anything. A small tube is inserted into your rectum and your colon is filled with carbon dioxide gas using a special machine. 2 scans are then performed, 1 with you lying on your back and a 2nd with you lying on either your side or tummy. Occasionally a 3rd scan may be needed so that we can see the whole of the large bowel clearly.

Are there side effects or risks from the procedure?

CT scanning involves x-rays so female patients who are, or might be pregnant must inform a member of staff in advance. The amount of radiation used is more than an ordinary x-ray of the chest or body and is equal to the natural radiation we receive from the atmosphere over a period of approximately 3 years. The risk from this radiation dose is however very low. You may have a contrast medium injected into a vein in order to increase the amount of information obtained from the scan. The injection usually causes nothing more than a warm feeling passing around your body. Mild abdominal discomfort and bloating can occur when gas goes into the colon and we use carbon dioxide gas because the body quickly absorbs it. Any symptoms quickly pass off when the tubing is removed from the rectum and you have gone to the toilet. Buscopan (muscle relaxant) can make your mouth dry and your vision slightly blurred (rare), which normally lasts 15-20 minutes.

This is very rare and has not happened in any of our patients having CT Colonography so far but perforation of the bowel can occur with this test (approximately 1 in 3000 tests). When it happens most cases resolve without treatment, but it may require hospital admission and observation under the care of a surgeon.  Despite these small risks, if your doctor believes it is advisable for you to have this examination, do bear in mind that there are greater risks from missing a serious disorder by not having it. This test can give additional information to the Consultant surgeon before or after an endoscopy procedure.

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