CT colonography (CT pneumocolon or virtual colonoscopy)

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

Part 1- CT Colonography examination

Please read all of the leaflet thoroughly before starting your preparation

This leaflet is for patients who are referred for a CT Colonography examination with faecal tagging. This procedure is also sometimes called a CT pneumocolon or a CT virtual colonoscopy. The leaflet will explain what the procedure involves and what the risks are.

What is CT Colonography?

‘CT’ stands for Computed Tomography, which means using x-rays to produce ‘sliced’ pictures through a part of your body, which can be reviewed by the doctor in two and three dimensions. CT Colonography is a test used to look at your large bowel (colon and rectum). In order to do this you will need to drink an oral contrast (dye) called Gastrografin the day before your appointment. During the scan a small flexible tube (about the width of a traditional pencil) is inserted into your back passage and carbon dioxide gas is gently introduced, to inflate your colon (large bowel). You will be asked to lay on the scanner table which then passes into the scanner, which is circular and has a large hole in the middle

The scanner is open at both ends and often referred to as doughnut-shaped. During the scan the table will move in and out the scanner as it takes images, and you will be asked to hold your breath. Each scan and breath hold is only for a few seconds.

The purpose of the test is to try and find out what may be causing your symptoms (for example, a change in bowel habit, weight loss, anaemia or rectal bleeding). You will need to prepare your bowel by drinking an oral contrast (dye) called Gastrografin and following a strict diet for 24 hours before your scan. It is important you follow the regime to ensure the pictures are good quality.

What happens during the examination?

Firstly, 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 and the small flexible tube will be inserted into your back passage (rectum) only a few centimetres. This will allow the radiographer to slowly introduce some carbon dioxide (CO2) and inflate the bowel which enables the doctors to see the walls of your bowel clearly. This may make you feel bloated and a little uncomfortable but it should not be painful.

Most patients are given two injections through the cannula. One is called Buscopan (an anti-spasmolytic drug) which reduces the natural movement of the bowel and makes it more comfortable for you. The other is an iodine-based (X-ray dye) injection to improve scan details in your abdomen and pelvis. Possible side effects from this injection is a brief warm sensation and a metallic taste. Scans will then be taken with you lying in different positions (usually on your right side and your back or your left hand side) to ensure we are able to see all of the bowel.

Please note that we have both male and female radiographers performing these examinations. They will also be accompanied by another radiographer acting as a chaperone during the examination.

If you would prefer a radiographer of the same gender as yourself performing your examination, please contact CT reception prior to your appointment so we can make prior arrangements to accommodate this.

How long will the examination take?

The whole examination will take about 30-45 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, these will ease as it is absorbed or released. You may also experience some residual diarrhoea which is due to the remaining preparation you drank the day before the scan. Please drink plenty of fluids and do not take any anti-diarrheal medication to counteract this.
• You will be asked to stay in the department for about 15 minutes after the scan. 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 and at this point you can start to eat and drink 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 regarded as 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, fewer than 1 in 3000 tests and can be seen on the scan.

There is a risk you may react to either the x-ray dye injection or the Buscopan. The radiographer will ask you questions to reduce this risk before giving you the injections.

Very rarely, the injection can cause painful blurred vision in people who are already at risk of glaucoma. If this occurs you should go to your nearest emergency department.

The bowel preparation may cause dehydration or an electrolyte imbalance. It is 1 important that you drink plenty of fluids. In some people it can also cause nausea and vomiting, skin rashes and very rarely an allergic type reaction.

• If you are concerned that you may be experiencing any of the above, please do not take any more Gastrografin and contact the CT department on 01223 217427 or 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 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?

CT colonography is the alternative test to optical colonoscopy. This involves passing a narrow flexible camera into the back passage into the colon 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.

Often CT colonography is used where the optical colonoscopy has not been successfully completed, which can be for a number of reasons.

A colonoscopy can only give information on the inside of the large bowel, whereas CT Colonography also 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 or radiographer specially trained to interpret this test. Your results will then be communicated to you by your referring team.

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 a liquid called Gastrografin and to follow a special low-residue diet the day before the appointment.

The Gastrografin may have a strong laxative effect, but this will vary from person to person. You may experience stomach cramps with the diarrhoea, 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 a lack of mobility when taking the Gastrografin, please give the CT Department a ring on 01223 217426.

During this time you will need to:

• Stay near a toilet at all times.
• Drink plenty of fluids as instructed to prevent dehydration.
• Continue to take your regular medication with the exception of Iron tablets
• 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 Gastrografin?

If you are taking Iron tablets please stop them for 7 days prior to your scan.

If you are taking any weight loss medication please stop them for 7 days prior to your scan.

You should continue with all your other regular medication as prescribed by your doctor unless directed otherwise.

Please DO NOT take Buscopan the day of your examination.

Additional Information

If you are a diabetic, please read the chart in this leaflet on page 8. The change in your diet may upset your diabetes. Monitor your blood sugar regularly. If you have any questions about controlling your diabetes whilst taking your preparation, please contact the diabetes nurse specialist.

If you are taking beta-blockers, hypersensitivity or allergic-type reactions may be aggravated. Please contact the CT department on 01223 217427 if this happens.

How do I take my Gastrografin?

The preparation for the scan is over a 24 hour period. Please start the diet and preparation the day before your appointment.

(Do NOT stop taking your normal medication except those detailed in the instructions below)

DAY BEFORE the examination

Before breakfast - 07:00

Mix 75mls (three quarters of the bottle) Gastrografin with an equal amount of water. Cordial may be added. Drink the liquid mixture

Breakfast – before 8am

This meal is limited to boiled or poached egg and/or white bread with a scraping of butter or margarine and/or a plain vegan yogurt .

Lunch – 12:30-13:30

A small portion of steamed, poached or grilled white fish OR chicken OR plain tofu +

a small portion of boiled potatoes (2 eggs sized) OR two slices of white bread.

After Lunch

NO SOLID FOOD to be eaten until after your examination.

Clear soup/broth, for example Bovril/Beet Bovril, may be consumed followed by jelly (this may contain sugar).

Evening - 19:00 –

Mix the remaining 25mls of Gastrografin with an equal amount of water. Cordial may be added. Drink the mixture

Please note –

Drink as much liquid as possible.

Tea and coffee WITHOUT milk are permitted.

Alcohol is NOT permitted.

THIS DIET IS IMPORTANT AS MILK AND FOODS ABSENT FROM THIS LIST CAN IMPAIR THE DIAGNOSTIC QUALITY OF YOUR SCAN IF CONSUMED.

Because food intake is limited you may require the occasional sugary drink.

DAY OF the examination

No solid food until after the examination.

If diabetic, do not take your diabetes medication until after the examination.

Advice for diabetic patients undergoing CT Colonography

Please follow these instructions if your procedure is in the morning (before 13:00). For any diabetes related questions during bowel preparation, please contact your GP or the diabetes specialist nurses on 01223 348790 or bleep 152078.

Is there a reason why I should not take the Gastrografin?

If you are hypersensitive to iodine-containing contrast media or have hyperthyroidism then you should not take the Gastrografin. Please contact the CT department for further advice.

If you are or think you might be pregnant, please contact the CT department on 01223 217427 before taking the medication.

Contact enquiries

Direct line to CT Scanning reception: 01223 217427

Please contact the CT department between 08:00 – 17:00 (Monday to Friday) as soon as possible if:

• you cannot attend for your appointment for any reason
• you are or there is any chance you may be pregnant
• you weigh more than 180kgs or 28 stone
• you are claustrophobic
• you have limited mobility
• In the lead up to your appointment you or someone you live with are suspected or confirmed of having COVID-19. This would be suggested by:
  • A positive COVID-19 test Fever of > 37.5 •C
  • New persistent cough
  • Myalgia – muscles aches
  • Difficulty in breathing
  • Loss of taste or smell
  • Nausea / vomiting
  • New diarrhoea (although please note that you do not need to call if diarrhoea occurs after you start taking Gastrografin, as this is an expected side effect)

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 01223 217427.

For further information

• Please contact the CT department on 01223 217427 between the hours of 09:00 – 17:00.
• See the website Bowel Cancer UK (opens in a new tab)

How to find us

The PET-CT department is between the outpatients and oncology departments on the ground floor. Parking at CUH is limited. Please use public transport if possible. If you do need to bring your car then we have two patient and visitor car parks.

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

My Chart

We would encourage you to sign up for MyChart. This is the electronic patient portal at Cambridge University Hospitals that enables patients to securely access parts of their health record held within the hospital’s electronic patient record system (Epic). It is available via your home computer or mobile device.

More information is available on our website: My Chart

Privacy & dignity

Same sex bays and bathrooms are offered in all wards except critical care and theatre recovery areas where the use of high-tech equipment and/or specialist one to one care is required.