Having a CT Colonography (CTC) Scan with Picolax and Omnipaque

What is CT Colonography and how is it performed?

Computerised tomography (CT) is a scan that uses x-rays to look at organs within the body. CT Colonography (CTC) is designed to look at the large bowel (colon) and abdomen. It is performed as an alternative test to a barium enema or colonoscopy. The examination is performed by a senior radiographer especially trained in CTC in conjunction with a radiologist and usually lasts for no longer than 30 minutes, although you may be in the department for up to an hour.

There will be another trained member of staff or radiography department assistant in the room during the procedure. You will be asked to change into a hospital gown when you arrive in the department which will be provided for you. You may bring your own dressing gown to wear on top if you wish.

Before the test a small tube (cannula) will be inserted into a vein in your arm. This will be used to give you an injection of a medicine to relax the bowel (Buscopan) and may also be used for x-ray contrast dye (iodine-based) during the scan.

A member of staff will take you into the scan room, ask you some questions and explain the procedure so that you understand what is happening. You can ask us any questions you may have at any time.

During the test, gas (carbon dioxide) will be used to inflate the colon via a thin flexible tube placed in your rectum (back passage). This will make you feel bloated and may give you some mild abdominal discomfort which should quickly ease when the test is complete. A CT scan will then be done with you lying on your back and then, either on your front, or on your side. Occasionally a third position will be required to get all the information required.

Are there any side effects or risks?

CT Colonography is a very safe examination and complications rarely occur.

CT scans involve x-rays; the amount of radiation used is more than an ordinary x-ray of the chest or body but is about the same as an average person receives from the atmosphere over approximately three years. The scanner we have in Dorchester has the latest software to keep the radiation dose to a minimum.

There is a tiny risk of making a very small hole in the bowel known as a perforation. This happens very rarely in 0.005% of cases. If this does happen, most cases resolve without treatment but may require hospital admission for observation.

If we need to give you x-ray dye, it can very rarely cause an allergic reaction which may need medication or even hospital treatment. This occurs in less than 0.04% of patients. More commonly it causes a metallic taste in the mouth, nausea or a feeling of warmth passing down your body. This usually passes very quickly.

The medicine used to relax your bowel can give you a dry mouth and make your vision a little blurred. This should resolve within half an hour, but you should not drive home until your vision has returned to normal. Very rarely, patients may develop pain and redness of the eyes within 24 hours following Buscopan. If this occurs, you should go immediately to the Emergency Department.

Are there any special preparations for this test?

It is very important that the large bowel is empty when this test is performed. You will need to follow a special low residue diet for a couple of days before the test and also take a strong laxative and a liquid called Omnipaque which you have already collected. Full instructions for the
preparation are below.

Pregnancy status

If you are or think you may be pregnant, please contact the department. If you are taking the oral contraceptive pill the bowel preparation may reduce its effectiveness, so continue taking the tablets but use other precautions for the remainder of that cycle.

After the examination

You will be taken to visit the toilet immediately after the scan has finished. The gas (carbon dioxide) is absorbed by the body and any discomfort should quickly wear off. If your vision has been affected by the Buscopan injection you should wait until your vision returns to normal before driving.

The x-ray dye is removed from your body by your kidneys; therefore, it is important to keep well hydrated over the subsequent 48 hours after your appointment.

The doctor who sent you for the examination should get the results within 10 days.

If you feel unwell after the test or have any questions or concerns, please contact the team on 01305 255397.

About this leaflet

Author: Simon Jones, Lead Radiographer CT
and Dr Kathy Lawrence, Consultant Radiologist
Written: February 2024
Updated and approved: February 2024
Review date: February 2027
Edition: v1

If you have feedback regarding the accuracy of the information contained in this leaflet, or if you would like a list of references used to develop this leaflet, please email patientinformation.leaflets@dchft.nhs.uk

Bowel preparation and diet sheet

Please follow these instructions carefully to make sure that your bowel is as empty as possible and to improve the accuracy of this test.

You should have received some laxative (Picolax) and a 50ml bottle of Omnipaque from the pharmacy. If not, please ring 01305 255397.

The Omnipaque contains iodine. It is very important that if you are allergic to iodine or have previously had a severe allergic reaction to x-ray contrast dye, if you have difficulty in swallowing or if you suffer from regular choking/coughing episodes when drinking fluids, that you do not take it and phone the department on 01305 255397.

If you have diabetes, please seek advice from your diabetic team about how to manage the diet.

Four days before

Continue to take any prescribed medicine, but if you are taking iron tablets you should stop taking them.

Two days before

If you are taking any constipating medicines such as Codeine, Kaolin and Morphine, Loperamide (Imodium), Regulan or Fybogel, stop this two days before you are due to come for the examination. Continue other medications and any laxatives you usually take.

Start low residue diet – you may only eat what is listed below throughout the day.

Foods allowed on low residue diet

• White bread and bread products, such as crumpets, wraps and white naan
• Breakfast cereals, such as Cornflakes, Rice Crispies, Special K or Frosties with a small amount of semi skimmed or skimmed milk, rice milk or soya milk
• White pasta, white rice, couscous, tapioca, ground rice, semolina, peeled potatoes
• Quorn, tofu
• Chicken or turkey
• White fish
• Boiled, poached or scrambled eggs (without cream or butter)
• Boiled sweets, fruit gums, pastilles, Madeira cake, plain biscuits eg rich tea, water biscuits, cream crackers, rice pudding and plain sponge
• Strained stock, stock cubes, Marmite, Bovril, soy sauce, instant gravy
• Clear fluids including water, fruit squash, fruit juice with no bits, rehydration drinks, clear soup or broth, tea/coffee with small amount of milk
• Small amount of oil for cooking, honey, lemon curd, golden or maple syrup, marmite, smooth peanut butter and jams or marmalades with no bits
• Salt, sugar, fine ground pepper, vinegar, mustard, gelatine, dried herbs, salad cream, mayonnaise, ketchup.

Foods not allowed

• All fruit including dried fruit and vegetables
• Wholemeal, granary, brown and high fibre white breads and bread products (including best of both)
• Potato skins and chips
• Crisps and nuts, fresh herbs, pickles, chutney, hummus, freshly ground peppercorns
• Biscuits or cakes made with wholemeal flour/nuts/fruit/grains (fruit cake, Ryvita, digestives, hobnobs)
• Whole wheat pasta, bran and brown rice or noodles
• High fibre breakfast cereals such as Weetabix, Shredded wheat, bran flakes, porridge
• Red meat including burgers, sausages and ham
• Pulses such as beans and lentils
• Fried or fatty fish
• Full fat milk, cream, full fat yoghurt, ice cream and full fat hard cheese
• Butter and butter-like spreads, vegetable oils
• Drinks to avoid are full fat chocolate drinks, drinks with full fat milk, cocoa and vegetable juices.

One day before

Continue the low fibre breakfast before 8am. After this, you must only have clear fluids from now until after your CT colonography. You must not eat any food or have any fluids which are not clear during this period.

Clear fluids include the following:

• Water
• Black tea and black coffee (without milk), herbal or fruit tea (no solids)
• Clear, strained soups (consommé, sieved Minestrone)
• Oxo, Bovril or Marmite drinks
• Clear jellies
• Clear fruit squashes and cordials
• Clear fruit juice (such as apple or grape)
• Boiled sweets
• Clear, fizzy drinks can be drunk but can make you feel bloated.

At 8am take the first sachet of Picolax. Prepare the Picolax by mixing the contents of one sachet in a cup of cold water (approximately 150ml) and stirring for two to three minutes. The solution may become hot. Wait until it has cooled down before drinking. You can flavour it with a clear squash or cordial if you do not like the taste. Some people find it easier to drink it through a straw.

Drink 30mls Omnipaque mixed with water/clear squash.

Continue to drink plenty of clear fluids (aim for one or two glasses an hour).

After two to three hours you should start to experience frequent bowel motions followed by diarrhoea. This will mean that you will need easy access to the bathroom. Some abdominal cramping is expected.

Advice regarding medication can be found within the information booklet. Please avoid taking medication within an hour of taking Picolax.

At 4pm take the second sachet of Picolax and 30mls Omnipaque. Remember to keep drinking plenty of clear fluids for the rest of the day. You will find that your stool (poo) becomes more liquid and clearer each time you open your bowels. By the morning it should be watery and fairly clear.

On the day of the scan, you can have clear fluids up to the time of the scan, but no solid food. After the scan you can eat and drink as normal and you may want to bring a snack with you to have in the department before going home