CT colonography (CT pneumocolon or virtual colonoscopy) – Iodine-free examination

• Part 1 - The examination
• Part 2 - Preparation instructions

Part 1 - CT colonography examination

Please read this leaflet thoroughly before starting your preparation.

This leaflet is for patients who have been referred for a CT colonography examination, which is also known as a 'CT pneumocolon' or a 'CT virtual colonoscopy'. This leaflet will explain what the procedure involves, and what the risks are.

Every year, thousands of people fail to keep their appointments. If you do not turn up, we cannot give your slot to someone else. If you are unable to attend, no longer need the scan or would like to re-arrange your appointment, please call CT Scanning reception on 01223 217427.

Please note that we have both male and female radiographers who perform these examinations. They will also be accompanied by another radiographer to act as a chaperone during the examination. If you would prefer a radiographer of the same sex as yourself to perform your examination, please call the CT Department on the number below before your appointment so that we can arrange this.

You will need to prepare your bowel for the test by drinking a 'contrast agent' and following a strict diet for 48 hours before your scan. This helps to ensure that the pictures are good quality.

What is CT colonography?

CT (computed tomography) uses x-rays to create ‘sliced’ pictures through a part of your body in two and three dimensions. These pictures are reviewed by the doctors. CT colonography examines your large bowel (colon and rectum) to try to find out what may be causing your symptoms (for example, a change in bowel habit, weight loss or anaemia).

The CT scanner is shaped like a doughnut. There is a large hole in the middle. The scanner table moves in and out of the scanner as it takes images.

About the examination

What happens during the examination?

First, the radiographer will explain the procedure, and answer any questions you have. You may be asked to change into a hospital gown to prevent any metal objects showing up on the pictures. The radiographer will put a cannula into one of your arms.

You will then be asked to lie down on the scanner table on your right side. A small, flexible tube will be inserted into your back passage a few centimetres. This will allow the radiographer to slowly introduce some CO₂ (carbon dioxide gas). This is done to inflate the bowel to enable the doctors to see the walls of your bowel clearly. The gas may make you feel bloated and a little uncomfortable, but it shouldn’t be painful.

Most patients are given an injection called Buscopan through the cannula. Buscopan is an anti-spasmolytic drug which reduces the natural movement of the bowel to make you feel more comfortable. Scans will then be taken while you lie in different positions (usually on your right side and your back or your left hand side) to ensure we can see all of the bowel.

How long will the examination take?

The whole examination will take about 30 to 45 minutes. Unless there are delays to the list, your total time in the department should be about one hour.

What should I expect after the examination?

At the end of the examination, the tube will be removed. You may want to visit the bathroom to expel some of the gas, although most of it will be absorbed inside or expelled naturally over the course of a couple of hours following the procedure.

You may experience some abdominal discomfort from the gas. This discomfort will ease as it is absorbed or released. You may also experience some residual diarrhoea due to the remaining preparation you will have taken before the examination. Please drink plenty of fluid, and do not take any medication to counteract this.

You will be asked to stay in the department for about 15 minutes. You will be offered a hot drink and something to eat (feel free to bring something else with you). After this time, we will remove the cannula and check that you are comfortable before you leave the department. You can then resume eating and drinking as normal.

If you received Buscopan for your scan, you may have blurred vision following the injection. Your eyesight will, however, return to normal within an hour. Do not drive or operate heavy machinery until your eyesight has returned to normal.

Are there any risks or side effects?

CT colonography is generally considered to be a safe test. Problems are rare and are similar to those which could happen with other methods of examining the bowel.

These include the following:

• There is a risk of making a small hole to the lining of your bowel wall. This is very rare (less than 1 in 3000 tests) and can be seen on the scan.
• Very rarely, the Buscopan injection can cause painful blurred vision in people who are already at risk of glaucoma. If this happens, you should go to your nearest emergency department.
• The bowel preparation may cause dehydration or an electrolyte imbalance. It is important that you drink plenty of fluids. In some people, it can also cause nausea and vomiting, skin rashes and, very rarely, an allergic reaction.
• If you are concerned that you may be experiencing any of the above, please do not take any more of the bowel preparations and call the CT Department on the number below, or contact your GP.
• Taking the bowel preparation might prevent the absorption of the oral contraceptive pill. Additional contraceptive precautions should be taken until your next period begins.
• As with all x-ray examinations, there is a small risk from the use of radiation. The dose is kept as low as possible and is equivalent to a few years of natural background radiation.

Are there alternative tests?

An alternative to CT colonography is optical colonoscopy. This involves passing a narrow flexible camera into the back passage to examine the colon lining. This remains the standard test for the large bowel. It is more invasive than CT colonography, and usually requires sedation. It does, however, allow tissue samples to be taken if needed.

CT colonography is often used when the optical colonoscopy has not been successfully completed. This can be for a number of reasons. A colonoscopy can only give information on the inside of the large bowel, whereas CT colonography provides extra information on the other structures within your abdomen.

When and how will I get the results of the examination?

The pictures taken of your bowel will be reported by a radiologist (specialist radiology doctor) and a report will be sent to your referring doctor, who will inform you of the results.

If you have an appointment booked, the results will be ready by then. If you do not have another outpatient appointment and you do not hear anything within three weeks, please contact the department that referred you for the scan.

Part 2 - How to prepare for your scan

What do I have to do before my CT colonography?

It is very important that you have a well-prepared bowel so that we can take good quality images. To do this, we will ask you to drink two liquids called Citramag and EZ cat and follow a special low-residue diet for two days before the test.

The Citramag may have a strong laxative effect, but this will vary from person to person. The EZ cat is a contrast agent to coat the lining of your bowels. This is important for image interpretation. You may experience stomach cramps with the diarrhoea, but this is normal. If you feel like your bowels are not completely clear, do not worry as its primary purpose is to act like a dye that coats the bowel wall and any liquid waste which shows up on the scan.

If you have concerns about your suitability for the procedure due to limited mobility when taking the bowel preparations, please call the CT Department on the number below.

During this time you will need to:

• always stay near a toilet
• drink plenty of fluids as instructed to prevent dehydration
• continue to take your regular medication
• use extra precautions if you take the oral contraceptive

If you have a stoma, please bring a spare flange/ baseplate and stoma bag with you to your CT appointment.

Can I take other medication along with Citramag and EZ cat?

• If you are taking iron tablets, please stop taking them for seven days before your scan.
• You should continue with all your other regular medication as prescribed by your doctor unless directed otherwise.
• Please do not take Buscopan on the day of your examination.
• If you are taking beta-blockers, hypersensitivity or allergic-type reactions may be aggravated. Please call the CT Department on the number below if this happens.

Is there a reason you should not take the bowel preparation?

If you are, or think you might be, pregnant, please call the CT Department on the number below before taking the medication.

Please call the CT Department as soon as possible if:

• you cannot attend your appointment for any reason
• you are, or there is any chance that you might be, pregnant
• you weigh more than 180kg (28 stone)
• you are claustrophobic
• you have limited mobility
• In the lead up to your appointment you, or someone you live with, has, or is suspected to have, COVID-19. This would be suggested by:
  • a positive COVID-19 test
  • a fever of above 37.5ºc
  • a new persistent cough
  • myalgia (muscle aches)
  • difficulty breathing
  • loss of taste or smell
  • nausea or vomiting
  • new diarrhoea (please note: do not call if you have already started taking your bowel preparations, as this is an expected side effect)

For further information

• Please call the CT Department on 01223 217427 between the hours of 08:00 (8am) and 17:00 (5pm), Monday to Friday.
• Refer to the Bowel Cancer UK (opens in a new tab) website.

How to find us

The PET-CT Department is between the Outpatients and Oncology departments on the ground floor. Parking is limited, so please use public transport if possible. If you do need to bring your car, please note that we have two patient and visitor car parks.

You can find information – including information on parking concessions – on our website at Visiting our hospitals.