CT (Computed Tomography) is the name of a technique that allows us to build up a cross sectional picture of the part of your body that is under investigation.
What is a CT?
The CT scanner is a large machine through which you will pass on a moving bed. The scanner uses X-rays and a powerful computer to take thin slice images of your body which can be looked at in any plane. These highly detailed images allow your medical team to help you make informed decisions about your healthcare.
Unlike the MRI Scanner, the hole in the middle of the CT Scanner is much larger and the tube through which you pass is much shorter. Most of the time you can see out of either one side or the other of the scanner and therefore it is less of a problem if you feel claustrophobic.
CT scanning is becoming used increasingly throughout radiology for investigating the whole of the body. It is particularly good at looking at areas that may contain gas (like the bowel or liver) that cannot be looked at with ultrasound. It also acquires its pictures much more rapidly than MRI and is much more available throughout the country than MRI and is therefore often the investigation of choice for many conditions, indeed you may find that we recommend a combination of techniques to build the best picture of you that we can.
Are there any Risks?
As CT uses radiation there are risks associated with the technique. Large doses of radiation have been shown to have adverse effects on the body, both in terms of damage to your skin body tissue and also in potential damage to your DNA.
It is important that you know that the techniques used in medical imaging are below the level that is associated with such effects and that the radiology team who care for you will work to ensure that the radiation dose you receive is both appropriate to address the question being asked and as low as it can be.
For female patients, if you are or may be pregnant, you must make sure the doctor referring you or a member of the radiology department knows as soon as possible.
CT is not usually advised in early pregnancy unless there are special circumstances.
What happens during the CT?
Following receipt of your appointment, you will often be asked to come to the department up to one hour before the investigation. This is to allow time for you to drink some dye, which enables the radiologist to see the bowel more clearly. This needs time to pass through as far as the colon. For investigations of bones or the chest, often you will come just shortly before your appointment time. Many of the investigations that are undertaken now also require the injection of dye into the arm. This dye contains iodine, it is not radioactive, but shows up as white areas on the scans, helping the radiologist to tell the difference between blood vessels and other structures. You will be asked about allergies and your tablets, to ensure that there is no risk of allergies or interactions.
When the radiographers are ready to scan you, you will be taken into the CT room and asked to lie on the couch.
How long will it take?
The scans themselves are often very quick, taking between 10 and 20 minutes to acquire. Whilst the pictures are being taken, we need you to lie as still as possible. For many of the investigations, you will also be given clear instructions on when to hold your breath. Many patients are worried about whether they will be able to lie still and hold their breath long enough. Don't worry about this, you will be given clear instructions to help you with any problems.
Unlike the MRI scanner, the CT scanners are often quite quiet.
Are there any side effects?
If you do receive an injection of contrast (dye) during the investigation, this will often make you feel warm, you may feel a metallic sensation in the mouth and some people feel as though they wish to pass water. Don't worry, you won't, it just gives you that sensation and these feelings pass quickly.
Do I need to have any special preparation?
As metal buckles and buttons can cause problems with the pictures, you will often be asked to either remove these items or put them in a position where they are not in the area to be scanned.
When you arrive
Please go to the reception desk detailed in your appointment letter. After this you will be shown where to wait until collected by a radiographer or other member of staff.
Can I bring a relative/friend?
Yes, but for safety reasons they may not be able to accompany you into the scan room, unless there are special circumstances.
Who will I see?
When you arrive, you will meet one of our receptionists. The scan will be performed by a specialist CT radiographer. Their training was initially as a radiographer and they will have subsequently spent specialist time training in CT scanning, working closely with the radiologists. They will ensure that you have had the correct preparation and often will ask you a number of questions to ensure that it is safe then perform the scan.
Can I eat and drink afterwards?
Yes you can.
When will I get the results?
At the end of the procedure, the computers collect all the information and start to process it. Whilst the radiographer can reassure you that the appropriate images have been obtained, they will usually not be able to give you any idea of the results at that time.
When the computer has manipulated all the images, the radiologist will look at the scan. As there can be in some cases be in excess of 1,000 images, the reports are not available immediately. The doctor who initially referred you should receive the report within the next few days or up to a week.
We hope your questions have been answered here but remember that this is only a starting point for discussion about your examination. Make sure you are satisfied that you have received enough information about the examination, before you sign the patient questionnaire and consent form and feel free to ask us any questions either via this site or via your referrer. We are here to help you.
Other sources of Information
Royal College of Radiologists
For health advice and information, visit the NHS website: