Having a CT Colonography Scan

Your doctor or nurse has recommended that you have a CT Colonography (CTC) scan. Please read all of this leaflet, it explains why you are having a scan and what is involved. It is very important that you have your CTC scan as soon as possible. If you can, please accept the soonest appointment that you are offered. You are having this test following an appointment with a doctor or nurse. If your health has got worse since that appointment, please contact the radiology department before you come for your scan.

What is CT Colonography?

CT Colonography (also known as a CTC scan) is a way of looking inside your bowel. It is normally used to rule out or diagnose bowel cancer. A CT machine uses x-rays and computers to create detailed images. We then look at these images to check the health of your bowel. Your scan will be carried out by a male or female radiographer who specialises in CTC scans. The examination usually takes around 30 minutes. If something unusual is seen on the scan you may need to have an endoscopy at a later date. This is so that a sample (biopsy) can be taken for further investigation. Your doctor or nurse will discuss this with you if it is needed.

Before your CTC scan

We need to make sure that the images of your bowel are as clear as possible. This means that your bowel will need to be clear of faeces (poo) before the scan takes place. You will need to take a mild laxative, which we call ‘bowel preparation’. You will also only be able to eat certain types of food during the days before the scan. You will be given a separate leaflet with instructions on what you can eat and when to take the bowel preparation. Please follow these instructions very carefully to help make sure that your scan is successful.

Existing Medication

• If you take any medication that cause bulk in your bowels (Fybogel or Normacol for example) please stop taking these 5 days before your appointment.
• If you take iron tablets, please stop taking these 5 days before your appointment.

The contraceptive pill

If you are taking the contraceptive pill you are advised to take additional precautions. This advice starts from when you first take the bowel preparation and for seven days after the test.

Diabetic patients:

How you manage your diabetes when taking the bowel preparation and fasting will depend on whether you take diabetic tablets or insulin. Please contact your usual diabetic care provider if you have any questions or require more advice. You should continue to take all your other medication and tablets as normal unless you have been advised not to by your doctor or nurse.

During your CTC scan

A specially trained Radiographer will perform your CTC scan. They will explain what will happen and look after you during your appointment. They may need to ask you further questions before they perform the scan. Please let them know if you have had any problems with taking your bowel preparation or fasting. You will also be able to ask any questions that you need to.

You have the right to have a chaperone with you during your CTC scan, as it is an intimate examination. Where possible, the chaperone will be the same gender as you. However, during very busy periods it may not be possible to have a chaperone as the same gender as you. If this would prevent you from having the CTC scan, please call the radiology department as soon as possible to discuss.

You will be asked to change into a hospital gown and use the toilet before your CTC scan. A member of staff will insert a small cannula (needle) into a vein in your arm. This may be used to give you an x-ray dye and/or a bowel muscle relaxant (Buscopan) during the test. The Buscopan will reduce any discomfort or colic. The dye is sometimes used to improve the detail of the images that are taken during the scan.

In the examination room, you will be asked to lie on the scan table on your left-hand side. A thin flexible tube (about the size of a little finger) will then gently be inserted into your bottom. The tube allows us to slowly and gently fill your large bowel with carbon dioxide gas. This helps us to get a better view of your bowel. The gas will be stopped at the end of the examination. You might feel some bloating and discomfort in your abdomen due to the gas.

The Radiographer will then ask you to lie in at least two different positions on the table. This is so that they can get the best possible images of your bowel. The Radiographer will leave the CT room whilst the scanner is in use. However, they will be able to see you through the scanner room window and hear you. You will be able to talk to them through an intercom system. When the scan starts you will be asked to hold your breath for a few seconds. You will then feel the table move slowly into the scanner. If for any reason you want the scan to stop, you can tell us. We will stop the procedure as soon as it is safe to do so.

After your CTC scan

At the end of the scan, we will gently remove the tube from your bottom. We will then ask you to go to the toilet before getting dressed. The Radiographer may ask you to wait while they check that no more images are needed. They will also check that there is no sign of allergic reaction to any dye you may have been given via the cannula. The carbon dioxide used to fill your bowel will be absorbed quite quickly by your body. You might experience some discomfort for the rest of the day, but this should be mild. You might wish to rest at home for the rest of the day, although most people are able to resume their normal daily activities. You can eat and drink as normal after the scan and resume any medication that you stopped ahead of the CTC scan. Please drink plenty of fluids after the scan, to make sure that you stay well hydrated.

Your scan results

A specialist will look at the images from your scan. They will send a report to the doctor or nurse who requested you have the test. This doctor or nurse will contact you to discuss the results. The person who performs your scan is not allowed to discuss the results of the scan with you.

Risks of having a CTC scan

There are some risks to having a CT scan. You have been recommended to have this scan because your doctor thinks that the benefits of the scan far outweigh any of the risks. There are risks associated with having a CTC scan whilst pregnant. If you are pregnant or think you might be pregnant, please contact the radiology department as soon as possible to discuss.

A CTC scan uses x-rays, which are a type of medical radiation which does carry a very small risk of causing cancer many years after the scan. The radiation that you receive during a CTC scan is about the same as few years of natural background radiation (from your surroundings). The risk of this is considered to be low. The department monitors radiation doses very carefully and always uses the lowest dose needed to take good quality images.

There is a small risk of damage to the bowel wall. This happens to less than 1 in every 3000 patients having a CTC scan. A small number of patients may have an allergic reaction to the x-ray dye. This is very rare, and severe allergic reactions happen to less than 1 in every 2500 patients. Most allergic reactions occur within the 60 minutes after the injection, and we will monitor you during this time. There is a very small risk that the x-ray dye can affect your kidneys. To minimise this risk, we will check your kidney function before the scan. There is also a small risk that the x-ray dye may leak out of the vein into the surrounding skin. This can cause swelling and a bruise. It happens to less than 1 in 100 patients.

Remember that you have been recommended to have a CTC examination because your doctor thinks that the benefits of the scan far outweigh any of these risks.

Common side effects of having a CTC scan

X-ray dye

During the procedure you may have been given X-ray dye to improve the quality of the images. This would have been given through a small cannula (needle) in your arm. You may experience the following side effects 30-60 minutes after being given X-ray dye:

• A warm or hot feeling
• A metallic taste in your mouth
• A feeling of needing to urinate
• Feeling sick
• Itching
• Rash

After your CTC scan, you might wish to rest at home for the rest of the day, although most people are able to go about their normal daily activities. You can eat and drink as normal after the scan. Please make sure that you drink plenty of fluids. The carbon dioxide gas that was used to inflate your bowel will be absorbed quite quickly by your body. You might experience some mild discomfort for the rest of the day. This is very normal and should ease with time.

Re-starting Medications

You may have been asked to stop taking some of your existing medications before your CTC scan. Please start your usual medications as normal when you get home from your scan.

Common Side Effects of Having a CTC Scan

X-ray Dye

During the procedure, you may have been given X-ray dye to improve the quality of the images. This would have been given through a small cannula (needle) in your arm. You may experience the following side effects 30-60 minutes after being given X-ray dye:

• A feeling of warmth, as if you have passed urine (wee).
• A metallic taste in your mouth
• Nausea (feeling sick)
• Vomiting (Being sick)
• Itchy rash
• A bruise where you had the injection.

Bowel Preparation Medication

Before coming to your appointment, you will have taken some medication to prepare your bowels for the scan. You may experience the following side effects after taking bowel preparation medicine:

• Headaches
• Nausea (feeling sick)
• Vomiting (being sick)
• Proctalgia (pain and spasm of the back passage).
• Diarrhoea
• Dehydration

Carbon Dioxide Gas

Carbon dioxide gas will have been used during the procedure to inflate your bowel. This was so that images could be taken of your whole bowel. You may experience the following side effects after being given carbon dioxide gas:

• Bloating in your abdomen (tummy) during and after the scan. This should slowly improve with time.

Buscopan

It is likely that you were given a medicine called Buscopan during the scan, via a cannula (needle) in your arm. This was to relax your bowel muscles to help us to take better images. You may experience the following short-term side effects after being given Buscopan:

• Dry mouth
• Temporary blurred vision (this should wear off within 30-60 minutes)
• Tachycardia (fast heart rate)
• Dizziness (this should wear off within 30-60 minutes).

If you experience blurred vision, please do not drive until your vision has returned to normal. In very rare cases, Buscopan can also cause urinary retention (being unable to pass urine) in some patients with underlying medical conditions. Please contact your GP or local accident and emergency department urgently if you suddenly develop symptoms of being unable to pass urine.

Rare but Important Side Effects Relating to Your Eyes

If you have a rare form of glaucoma (called narrow or closed-angle glaucoma) it is possible that using Buscopan can lead to high pressure within your eye. This reaction is very rare. However, if it does happen you MUST immediately seek help. If the symptoms are treated early, the side effects can normally be managed with no long-term effects to your vision. If left untreated there is a risk of vision loss. Please note that most patients with glaucoma in the UK have open angle glaucoma. This means they are not at risk of this reaction.

Symptoms to Watch For

Please seek help using the instructions below if you experience the following symptoms after your CTC scan:

• Eye pain or brow ache together with any of the following:
  • Halos (bright, colourful circles that appear around lights)
  • Reduced vision (please note that many people have some blurring of vision after receiving Buscopan. However, this usually wears off after 30-60 minutes and is not associated with eye pain).
  • Red eye – the white part of your eye looking red or ‘blood-shot’.
  • Persistent nausea (feeling sick) or vomiting – please note that nausea is also a common side effect of other medications used during a CTC scan. However, this usually passes quickly. Persistent nausea or vomiting together with other symptoms listed above may be related to high pressure in your eyes.

How to Seek Help with Eye Symptoms

You can get emergency advice from some local opticians through the NHS Community Urgent Eyecare Service. This is free of charge if you are registered with a Greater Manchester or East Cheshire GP Practice. You can find information about the service by visiting this link: https://primaryeyecare.co.uk/ You will need to use the website to find your closest optician who offers this service. Contact the optician to make an appointment before visiting. Take this leaflet with you to your appointment.

If you have symptoms outside of working hours, you cannot get a same-day appointment or you are not registered with a GP practice, please seek emergency eye care via:

• Manchester Royal Eye Hospital Eye Emergency Department (24h)
• Stepping Hill Hospital A&E (24h)
• Bolton Royal Hospital A&E (24h)
• Rochdale Infirmary Urgent Care Centre (24h)

Emergency eye care can also be accessed at Royal Albert Edward Infirmary A&E between the hours of 9am and 5pm.

Other Side Effects That Require Urgent Medical Advice

Most side effects following a CTC are mild and should ease with time. Please seek urgent medical advice from your GP, NHS 111 or your local accident and emergency department if necessary.

Please visit the emergency department if you experience any of the following symptoms during the 4 days after the procedure:

• Severe abdominal (tummy) pain that does not get better.
• Continued sweating, nausea (feeling sick), or vomiting.

Your Scan Results

A specialist will look at the images from your scan. They will send a report to the doctor or nurse who requested you to have the test. This doctor or nurse will contact you to discuss the results.

How can I provide feedback?

We want to hear your feedback about your CTC scan. We have a feedback form, which you can access using the QR code below. Alternatively, you can ask for a paper version of the form when you are at your appointment.

Last modified 18th September 2025 08:30:41 am