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MRI service

Magnetic resonance imaging 

What is an MRI scan?

MRI stands for magnetic resonance imaging. A combination of strong magnet and radiowaves produce detailed pictures of the inside of your body. Unlike x-rays and CT (computerised tomography) scans, MRI scans do not use radiation.

An MRI scan to help us find the cause of your problem and the best treatment options for you. MRI scans are particularly good at identifying problems in the spine, brain and joints. A standard x-ray does not give the same level of detail as an MRI scan.

Where to find us

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


Having a scan

  • How to prepare for your scan

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

    The scanner is a short tunnel, so if you suffer from claustrophobia (fear of enclosed spaces), please let us know before you come for your scan. 

    Please wear clothes that are easy to remove as you will be required to change into a hospital gown and trousers before you have your MRI scan.

    No metallic items, such as coins, watches, mobile phones or cards with a magnetic strip, such as credit or oyster card, can go through the scanner. Lockers are provided for your clothes and valuables.

  • 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.

  • Are there any risks?

    An MRI is a very safe procedure, but patients with heart pacemakers and certain surgical implants, eg cochlear implants, cannot be scanned. You will be asked to complete a safety questionnaire before your scan to make sure it is safe for you to be scanned. If you cannot have an MRI scan, you may be able to have a CT or ultrasound scan instead.

    Sometimes we need to give you an injection of contrast dye before the scan. This contains gadolinium, which some people are allergic to. Very rarely it can cause an allergic reaction which is similar to hay fever (runny nose and itchy eyes).

    If you are pregnant, national safety guidelines recommend that we do not carry out an MRI scan unless it is clinically urgent. The doctor who refers you for the scan will decide with the radiologist (doctor who uses x-ray to diagnose and treat illnesses) if your scan is necessary. Many pregnant women have had MRI scans with no reported problems. For further information call the number at the top of this page.

  • What happens during a scan?

    MRI scannerThe radiographer will ask you to lie on the scanner bed and position you correctly. You will need to keep very still during the scan to avoid blurring the pictures. 

    If we are scanning your chest or abdomen, we may ask you to hold your breath for a moment.

    The scan should be completely painless. The most difficult part is keeping still. However, it makes a loud banging noise. We will give you headphones to reduce the noise. You can listen to music, so please bring in a CD.

    Listen to the noise you will hear during your scan.


    A scan usually takes 20-30 minutes, depending on the area of your body that is being scanned.

  • What happens after the scan?

    As soon as the scan is finished, you can go home or back to your ward if you are an inpatient.

    You can eat, drink and resume normal activities straightaway.

    The results will be sent to the doctor who referred you and a follow up appointment should be made for you to receive the results within the time specified by your doctorFor urgent problems, the results will be available sooner.

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


St Thomas' Hospital
Tel: 020 7188 9033

Guy's Hospital
Tel: 020 7188 5526

Cancer Centre
Tel: 020 7188 9033 or
020 7188 5526

Access guides

Accessibility information about the Cancer Centre at Guy's