CT Colonoscopy

This leaflet answers some of the questions you may have about having a Computed Tomography Colonoscopy (CTC) scan. It explains the risks and the benefits of this test, and what you can expect when you come to hospital. It also explains how to prepare. If you have more questions at any time, please do not hesitate to ask a member of staff.

What is a CTC scan?

A CTC scan is a type of x-ray that allows us to take 3D pictures of your large bowel (colon) and abdomen (tummy). It is also known as a virtual colonoscopy.

You lie on a scanning table. You will have scans in two or three positions: on your back, on your side, or laying on your front.

So we can get a good view, we need to pump some air or carbon dioxide into your bowel. This helps to open up your bowel, to make it easier to see on the computer. This is done before your scan. We put the gas in through a small, thin tube that is put into your rectum (bottom).

How long does it take?

The scan usually takes about 20 to 30 minutes but you should expect to be at the hospital for about one hour.

Why do I need this test?

Your hospital specialist has recommended you have this test. You usually have it to help us find the cause of your symptoms and to make a diagnosis. It is important that you understand why you are having this test. If you are not clear about the reasons, please check with the senior radiographer who sees you on the day of your test.

What are the benefits?

• CTC is less invasive than a normal colonoscopy. You might find that you can tolerate this procedure much more easily, as it causes less discomfort and is quicker.

• If you are having a CTC, you will only need to follow a low-fibre diet for one day. Whereas if you are having a normal colonoscopy, you will need to follow the low-fibre diet for three days.

• A CTC can help us to reach a diagnosis to make sure we give you (or you are already on) the best treatment.

What are the risks?

This test is safe and serious complications are rare.

When you have a CTC scan you are exposed to a small amount of x-ray radiation. This is equal to the radiation you get naturally from the atmosphere over about three years. The risk from this radiation dose is very low.

If you are, or think you may be pregnant, you must call the department before your scan on 01843 234565.

• Mild abdominal discomfort and bloating

  You may feel bloated and have tummy discomfort when the gas is put into your colon. We will check you during your procedure to make sure you are not too uncomfortable. The gas is absorbed quickly by your body. The symptoms do not take long to pass when the tubing is taken out of your bottom.

• Dry mouth and blurred vision

  You may be given a drug called Buscopan to relax your muscles and make your scan more comfortable. This can make your mouth feel dry and your eyesight slightly blurred. These symptoms normally last for about 15 to 20 minutes.

  Very rarely, Buscopan can cause eye pain or redness up to 24 hours after your test. If this happens, go immediately to your nearest Emergency Department for a check-up.

• Bowel perforation

  There is a rare risk (about one in 3,000) of damaging your bowel during the test. If this happens, your bowel usually heals without treatment. But you may need to be admitted to hospital and observed in case you need surgery to repair the damage.

If you have any of the following symptoms within four days of your scan, please seek urgent medical advice from your GP. Out of hours, go straight to your nearest Emergency Department.

• Severe abdominal (tummy) pain.

• Painful tummy discomfort that gets worse.

• Sweating and nausea (feeling sick).

• Feeling generally unwell.

Are there any alternatives?

Other tests include a colonoscopy. We cannot take samples with a CTC, so if we find abnormalities you may need a colonoscopy. Discuss with the doctor who sent you for your CTC whether the other tests are more appropriate.

Why do I need to sign a consent form?

All patients must give permission before they receive any type of medical treatment, test, or examination. Consent is usually given when you sign the consent form before your treatment, but we may ask you to give it verbally.

• You must give your consent voluntarily.

• The hospital must give you all the information you need to make a decision about your treatment. This is so you can give us informed consent.  If you have not been given this information, or you have but you still have questions, please speak to a member of staff. 

• You must be capable of giving consent. This means that you understand the information given to you and can make an informed decision.

When we ask you to give consent, please use this time to ask any questions you may still have. For more information, please read NHS: Consent for Treatment. Remember, you can withdraw your consent for treatment at any time.

Is a CTC scan painful?

No, but you may have some mild tummy discomfort and bloating during the test from the gas we put in your colon.

Do I need to stop taking my normal medication?

• Do not take any bran, anti-diarrhoea medication, bulk-forming agents, or iron tablets for four days before your scan.

If you are taking any other medications, you can take these as usual unless your doctor has advised you otherwise.

Please note: if you take an oral contraceptive, it may not work as well during this time. You must take other contraceptive precautions.

How do I prepare for my CTC scan?

We need to get a clear view of the inside of your colon, so it must be as clean as possible. If we cannot get a clear view you may need to have the scan again.

On the day before your scan you need to:

• eat a special diet

• drink a laxative called Picolax, and

• drink a contrast dye called Omnipaque.

Picolax

We will send you two packets of a laxative called Picolax. You mix this with water and take it the day before your scan. It helps to clearly show your colon on the scan. You may need to go to the bathroom more after the first dose, so make sure you are close to a toilet.

Omnipaque

We will also send you a small bottle of contrast dye called Omnipaque. You take this the evening before your scan. This is to help with faecal tagging, which is the labelling of faecal residue in your colon.

The Special diet preparation instructions below explain how and when to take the Picolax and Omnipaque.

If any of the following apply to you, do not take the Picolax or Omnipaque, and contact us on 01843 234565.

• You have tablet-controlled or insulin-dependent diabetes.

• You have ever had an allergic reaction to x-ray dye (contrast medium) containing iodine.

• You have had a biopsy of your large bowel in the last two weeks.

• You have had a biopsy of your prostate in the last two weeks.

• You have sickle cell anaemia.

Special diet preparation

You must follow this diet to clean your colon properly. If there is too much faeces in your bowel we will find it difficult to diagnose or monitor your condition, and you many need to come back at a later date to have the scan again.

Two days before your CTC scan

• You will need to stop eating any food at 10pm. Do not have anything to eat until your test is completed.

• You may drink clear soup and have ice cream or jelly.

The day before your CTC scan

• Step 1

  • You must drink at least 140mls of fluids every hour on the hour during the day.

    You may drink as much fluid as you wish at other times (for example tea, coffee with milk and sugar as desired, water, and squash).

  • If you feel weak or hungry, you can suck barley sugar or other sweets.

• Step 2

  • At 8am dissolve the laxative powder from one of the envelopes of Picolax into four dessert spoonfuls of water. The solution will get very hot.

  • Wait five minutes, then add more cold water to make 140mls of fluid.

  • Then drink it all.

• Step 3

  • At 4pm, repeat step 2 with the second envelope of Picolax.

• Step 4

  • At 8pm mix the 50ml bottle of Omnipaque with 300mls of water and drink it all. Although the bottle of Omnipaque states for 'IV use', for this examination it has to be drunk.

Special diet preparation if you have diabetes (type 1 and type 2)

If you need further advice, please contact your diabetes nurse specialist.

• You are at risk of having a hypo if you go without food for any length of time. To avoid this, please check your blood sugar regularly.

• You can drink clear fluids at any time, including fizzy drinks, fruit juice, and Lucozade.

• If you are diabetic and use insulin, please follow the instructions below.

Preparation using insulin and Picolax

The following advice is for diabetics who are insulin-controlled only. All other patients should follow the instructions listed above. This preparation starts one day before your CTC scan.

Make sure you have a morning appointment for your procedure.

Continue taking your insulin throughout the day and evening.

On the day before your examination at 2pm

• Dissolve one sachet of Picolax in four dessert spoonfuls of water. The solution will get hot.

• Wait five minutes, then add cold water to make up 140ml of fluid.

• Then drink it all.

You must drink plenty of fluids once you have taken the Picolax. You should be prepared for frequent bowel movements within three hours of taking Picolax. You may have some cramp-like discomfort.

If you have any questions or queries, please contact us on 01843 234565, and select option 3.

What happens before my CTC scan?

• Before your scan, staff will ask your name and date of birth and for you to confirm your address. If we do not ask these questions, please ask us to check. Ensuring your safety is our primary concern.

• You will be asked to change into a hospital gown. You can bring a dressing gown to wear if you like.

• Before you go into the scan room, you may have a cannula (thin plastic tube) put into a vein in your arm. This is so we can give you a muscle relaxant called Buscopan during your scan. This helps to reduce spasms in your bowel wall, and can make the examination more comfortable.

• We may also use the cannula to inject a special x-ray dye (contrast medium) into your vein, so we can get a better look at your colon. The dye usually causes you to feel a warm ‘flush’ pass around your body.

What happens during my scan?

• When you go into the scanning room, we will ask you some questions and explain the procedure to you. You can ask us questions at any time.

• We will ask you to lie on your side on the scanning table.

• You may feel like you need to go to the toilet or pass wind. This is normal, but try to keep in as much gas as you can.

This short video gives an overview of what a CT Colonoscopy is and what to expect on the day of your appointment. Please note this video may not be exactly what happens for all patients; your healthcare professional will advise for your personal requirements.

How will I feel after the scan?

After your scan you may feel bloated, have stomach pains, and pass wind. This does not last long. Once this has passed you can eat and drink normally again.

When will I get my results?

The hospital consultant / specialist looking after you will contact you to discuss your results.

Can I drive myself home after my scan?

If you have an injection during your scan (which is usual), we advise that you have somebody drive you home afterwards. If you do not have someone who can take you home, you must remain in the hospital for a few hours after your scan.

Who can I contact with queries and concerns?

If you have any questions, please contact us on 01843 234565.

This leaflet has been produced with grateful acknowledgement from King’s College Hospital NHS Foundation Trust.