CT Colonography Information For Patients

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CT Colonography is a way of looking inside your bowel and abdomen. This information explains how it is done, what to expect, and the risks involved.

What is CT Colonography?

CT Colonography involves using a scanner to produce two and three dimensional images of the whole of the large bowel (colon and rectum).

The scanner uses X-rays to produce images of a “slice” through a part of the body. This is called Computed Tomography or CT. 

During CT Colonography, gas (carbon dioxide) will be used to inflate your bowel via a thin flexible tube placed in your back passage. Then CT scans will be performed with you lying on your back and either your front or side. After the scans, doctors will look at your images for polyps and signs of cancer. If anything unusual is seen on the images, or if further information is needed, you may be offered further tests.

CT Colonography also provides information about the other structures inside your abdomen.

Are there alternatives to CT Colonography?

Endoscopy is the standard way of examining the large bowel. In this a thin tube with a camera on the end (colonoscope) is passed into the back passage and moved up and around the bowel. The procedure is more invasive than CT colonography and usually requires sedation. However, it does allow tissue to be removed for testing (biopsy) or polyp removal if needed. 

Important information

If you need an interpreter please inform the CTC service on 07826 513567 when we book your appointment or the doctor who requested the scan so that it can be organised before your appointment date. Relatives and friends are not permitted to assist with translation.

You should continue to take your prescribed medications as normal, except iron tablets which should be stopped three days before your CT Colonography.

Please let us know when you arrive for your test if you have any of the following:

  • Diabetes.
  • Kidney problems.
  • Prostatism.
  • Anginaor other heart problems.
  • You have had a reaction to iodine based intravenous contrast medium (X-ray dye) if you are not sure about this, please ask us.
  • Myasthenia Gravis.

Frequently asked questions and answers

Q. I have already had a colonoscopy that was difficult; how is this test different?
A. This test will be easier and more comfortable than trying to pass the endoscopearound your bowel.

Q. I have diabetes; can I still take the bowel preparation?
A. Yes. You have also been provided with an information sheet with additional guidance for patients with diabetes.

Q. Is this test just for my bowel or will it show anything else?
A. With this test it is possible to get informationabout other structures within your abdomen; the amount of information will vary for each patient, depending on thetechnique used.

Q. This test involves radiation; how much radiation will I receive and is it dangerous?
A. We use as little radiation as we are able to, whilst making sure that the scan is of adequate quality. The amount of radiation needed will depend upon various factors including the reason why the scan is being performed and if additional scans are required. 

Q. Will I have sedation for this test and will I be able to drive home afterwards?
A. Sedation or pain relief is not needed for this test. Most people find that it can be a little uncomfortable, but as soon as the test is finished the discomfort will ease. Because there is no sedation, this test will not affect your ability to drive.

Q. What happens if an abnormality is found in my bowel?
A. Usually you will get the result of your scan from the doctor who asked us to perform it. You and your doctor will then decide what to do next if any treatment is needed. However, sometimes if further tests are required we may try to organise them for the same day, especially if this means you do not have to have another bowel preparation.

Q. If polyps are found in my bowel, will I have to have them removed.
A. Your doctor will discuss this with you. Generally, polyps measuring 1cm or more will be removed at endoscopy, but smaller polyps may be left and monitored by follow up scans. This decision is made on an individual basis and will not be the same for everyone.

Q. Is this test as accurate as colonoscopy?
A. A large study has been performed, comparing this test to other bowel tests. This test has been shown to be as accurate as colonoscopy for identifying polyps over 6mm in size.

Q. Can anybody have this test?
A. As this test uses radiation, we try to avoid performing this test on anyone under the age of 40, however we treat every case individually and there will always be exceptions.

Q. What if I don’t want this test or cannot attend?
A. Please let us know as soon as possible so we can book another patient who is on our waiting list on 07826 513567. Please leave a message if we are unable to answer your call.

On the day of your test

Please attend the Radiology (X-ray) department at the hospital where you have been appointedand report to the CT reception desk. Your appointment letter will state which hospital you need to attend.

You will be greeted by a radiology assistant or radiographer and guided to the preparation area to get changed into a gown.

If you need help with changing you may bring someone with you to help you. 

What happens during CT Colonography?

  • The radiographer will explain the test and answer any questions,beforeasking for your consent. Please let them know if you had any problems with your bowel preparation.
  • The procedure usually takes about 15-20 minutes.
  • You may have a small tube, called a cannula, inserted into one of the veins in your arm.
  • A muscle relaxant will normally be injected via the cannula in your arm to avoid bowel spasm.
  • You may be given an iodine-based intravenous contrast medium via the cannula.
  • You will be asked to lie down on the scanner table on your left side.
  • The radiographer will pass a small flexible tube into your back passage.
  • Gas (carbon dioxide) will be gently introduced into your bowel through the tube in your back passage. This is done at a controlled rate by a machine specifically designed for the purpose.
  • Despite the muscle relaxant, you may still feel some bloating and mild discomfort in your abdomen like “bad wind”.
  • Once the radiographer is satisfied with the amount of gas in your bowel, CT scans will be taken with you lying in 2 positions.
  • Sometimes the radiographer may need to take extra scans to ensure we can fully see your entire bowel. Occasionally we will perform a scan of your chest at the same time for additional information.

Are there any risks?

CT Colonography is generally regarded as a very safe test.

Problems can occur, but they are rare. Problems which might occur are similar to those which can happen with other methods of examining the large bowel. These include:

  • Abdominal discomfort.
  • “Faint-like” reactions.
  • Allergic reaction to the injected contrast.
  • Damage to the bowel wall (there may be a small tear in the lining of the colon or rectum; this happens in less than one in 3000 tests and is called a bowel perforation).
  • Dehydration or an electrolyte imbalance caused by the bowel preparation. It is important that you drink plenty of fluids – your leaflet explaining the preparation for CT Colonography will give you this information.

If you feel very unwell after taking your bowel preparation, please do not take any more and contact us or your doctor (or out of hours GP service for weekends/evenings).

What happens after the test?

A specialist radiologist will review the images from your CT Colonography and send a report to the doctor who requested your scan.

Same-day endoscopy

Most patients will go home immediately after the test. We may occasionally be able to offer some patients a ‘same-day’ endoscopy when further information about the bowel is needed. When this happens, we will need you to stay in the hospital (or be available on a phone) fasting, for up to two hours after your CT Colonography test while we fully review your scan and arrange the endoscopy appointment. If same-day endoscopy is offered, you will be informed about what this examination will involve and escorted to the Endoscopy Unit.

Who should I contact if I want further information?

If you have internet access, you can find out more about CT Colonography on the National Institute of Clinical Excellence website: https://www.nice.org.uk/guidance/ng151

Contact details

If you have questions about the time or date of your appointment, please phone our appointment desk:

Monday to Friday: 8.30 a.m. to 4.00 p.m. on 07826 513567

If you have questions about the procedure, please contact us on the following number:

Monday to Friday: 8.30 a.m. to 4.00 p.m. on: 07770 784911 

If your call cannot be answered, please leave a message including your name, hospital number, your contact phone number and a brief message and we will return your call as soon as possible.

Additional information for patients with diabetes

This information is in addition to the instructions you may have additionally received for bowel preparation. Please follow the instructions for bowel preparation carefully.

With diabetes you are at an increased risk of having a ‘hypo’ (low blood sugar-symptoms include sweating, shakiness, blurred vision, light-headedness) when not eating for any length of time. To avoid this, we recommend you follow the instructions as below and please regularly check your blood sugar if able. Please make sure you have additional glucose drinks/glucose tablets at home. If you are concerned about the preparation for your test please contact your GP or the X-ray department.

Examples of suitable glucose drinks include; Lucozade, fizzy drinks, and clear fruit juices (but not diet or non-sugar versions).

Two days before your test

Take all diabetes medication as normal.

Day before your test

  • Follow dietary instruction.
  • Take Insulin/Diabetes tablets with any of the listed items on the diet sheet (i.e. clear soup, jelly, ice cream etc).
  • But reduce your Insulin doses by half. Continue taking Diabetes tablets.
  • You can continue drinking plenty of fluids right up to the procedure. Make sure you have glucose drinks regularly (i.e. 100 ml glucose drink every 2 hours).
  • Check blood sugar if able.

Day of your test

Morning of your appointment:

  • DO NOT take Insulin/Diabetes tablets.
  • Recheck blood sugar if able prior to arrival to hospital.
  • You can continue drinking plenty of fluids right up to the procedure. Make sure you have glucose drinks regularly (i.e. 100 ml glucose drink every 2 hours).
  • Bring Insulin/Diabetes tablets and a snack/drink with you to the hospital to have after the procedure if needed.

After your appointment:

  • Eat normally, but continue to drink plenty of fluids for the next couple of days.
  • Recheck your blood sugar if you are able to.
  • Take all medication as normal, unless advised otherwise during the scan appointment.

General Trust Information

Patient Advice and Liaison Service (PALS)

PALS is a confidential service for people who would like information, help or advice about the services provided by any of our hospitals. Please call 0800 783 4372 between 9.30 a.m. and 4.30 p.m. or e-mail lnwh-tr.PALS@nhs.net. Please note that this service does not provide clinical advice so please contact the relevant department directly to discuss any concerns or queries about your upcoming test.

CT Colonography Information For Patients. Version 4. Produced: May 2011. Latest review: August 2023. Review date: August 2026

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