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Having a CT scan

Computerised tomography

We have CT scanning facilities at Guy's Hospital, the Cancer Centre at Guy's and St Thomas' Hospital. Please remember to check your appointment letter before you come for your scan. 


What is a CT scan?

CT stands for computerised tomography. A CT scan uses x-rays to take detailed pictures of the inside of your body. It helps us find the cause of your problem and the best treatment options for you. A standard x-ray does not give the same level of detail as a CT scan.

  • Preparing for your scan

    Check your letter for any specific information about preparing for your CT scan.

    If you are taking medicines for diabetes, eg metformin, these may need to be altered around the time of the scan. As soon as you receive your appointment letter, call us for advice on 020 7188 5542.

  • Are there any risks?

    CT scans use radiation, however the dose used is very small. The benefits of the scan are thought to outweigh any risks.

    Sometimes we need to give you an injection of contrast dye before the scan, to help us see your internal organs better. This contains iodine, which some people are allergic to. Before your scan we will check whether you have had any previous allergies.

  • Giving your consent

    The radiographer will ask you if you are happy for the scan to go ahead. This is called verbal consent and may only involve the radiographer checking you are booked for the correct scan. If you do not wish to have the scan or are undecided, please tell the radiographer.

    It is your decision and you can change your mind at any time. Please bear in mind that not having the scan may delay your diagnosis as the doctors may not have all of the information that they need. Please remember that you can ask the radiographer any questions you have at any time before, during or after your scan.

    Please have a look at our consent policy for more information.

  • What happens during a CT scan?

    Radiographer operating a CT scannerThe radiographer will ask you to lie on a motorised bed, which will move slowly through the scanning machine. Unlike some machines, the CT scanner is not enclosed.  

    You will need to lie very still while each picture is taken, to avoid blurring the images. You may also be asked to hold your breath for a moment.

    You should not feel any pain during the scan. The most difficult part is keeping still. If you find it difficult or uncomfortable lying still, please tell the radiographer.

    A scan usually takes 10-20 minutes, depending on the area of your body that is being scanned. If any preparation is needed, you may need to come to hospital one hour before your scan.

    Please be advised if you need an injection of contrast dye one of the CT staff will insert a small needle into a vein in the back of your hand. When it is injected, you might feel a hot flush and get a metallic taste in your mouth. Sometimes people have a sensation that they are wetting the bed (but they don't actually do it). These sensations are normal and pass within minutes.

    If we are scanning your abdomen, we may need to give you a drink which has contrast dye (or sometimes water). Try to avoid passing urine until your scan is over.  

  • What happens after the scan?

    In most cases, you will be allowed to go home or back to the ward if you are an inpatient. You can eat, drink and go back to your normal activities straight away.

    If you have had a contrast dye injection, you may need to wait 10 minutes before you can go.

    Your results will be sent to your referring consultant or GP within 2 weeks. A follow up appointment should be made with with your referrer of obtain the results of the scan.

    If you are an inpatient, the results will be given to the doctors looking after you on the ward.