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MRI scan

MRI is a special technique that uses powerful magnets, radio waves and computers to produce detailed images (or scans) of the inside of your body. MRI stands for magnetic resonance imaging. 

There are many reasons your doctor might suggest you have an MRI scan. It might be to diagnose or monitor a disease or to find out more about your medical condition to help plan your treatment

The images taken in an MRI scan are very detailed. They’re taken in thin 'slices' through your body and can be taken from various directions. The images show your bones, soft tissues such as muscle, skin, nerves and blood vessels, and organs such as your brain and heart. The pictures created by an MRI scan can help show the differences between healthy and unhealthy tissue. 

An MRI scan can often show things that can’t be seen on an X-ray or in other tests such as an ultrasound. Unlike X-ray machines and CT scanners, an MRI scanner doesn’t use radiation. 

An MRI scan isn’t suitable for everyone. The magnetic field from an MRI scan affects some types of metal, such as surgical clips or pins. If you have any of this metal inside your body, the magnets can make it move, which might harm the nearby tissues. The metal may also interfere with the scanner getting a good picture.

The magnetic field may also affect some implanted electronic devices (like pacemakers) so they don’t work properly or even heat up. You can’t usually have an MRI scan if you have: 

  • a heart pacemaker or defibrillator (a device that keeps your heart rhythm regular)
  • an inner ear hearing aid (cochlear implant)
  • an aneurysm clip (a metal clip on an artery in your brain) 

If you’re pregnant, there’s no evidence that MRI scans can harm your baby. However, just to be safe, you wouldn't usually be offered an MRI scan if you’re pregnant, particularly in the first three months. If you’re pregnant, or think you might be, tell your radiographer before your MRI appointment. If you need to have an MRI scan while you are pregnant, the scan will be done in a way that minimizes any risk to your baby. 

We’ve given a general overview here of what you can expect if you’re having an MRI scan. But the exact details about the procedure may differ depending on your own circumstances. You can discuss this more with the health care staff responsible for your care.
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An image showing a person having an MRI scan

Details

  • Preparation Preparing for an MRI scan

    An MRI scan is usually done in the outpatient department of your hospital. This means that you have the scan and go home the same day. 

    You should eat, drink and take your medicines as you normally would before your scan unless you’re told otherwise. If there’s anything particular you need to do before your scan, you will be told in plenty of time. You may, for instance, be asked not to eat for an hour before your scan. 

    If you have claustrophobia, you should tell your doctor when he or she suggests that you have the scan. You should also contact the hospital before the day of your scan to tell the radiographer who performs the test. For more information about what can be offered to help prevent claustrophobia during an MRI scan see our FAQs. 

    Sometimes a special dye (contrast medium) is used during an MRI scan to produce more detailed images. If you have kidney problems, you may need a blood test before your scan to check how well your kidneys are working. If your kidneys aren’t working well enough you may not be able to have the contrast medium. 

    At the hospital, your radiographer will ask you to complete and sign a safety questionnaire. You will be asked about any medical conditions you have. You’ll also be asked if you have any metal or electronic implants in your body as these might cause problems during your scan. To help you think about this your radiographer will give you a checklist of metal items that might be inside your body. They will go through this with you. If you’re not sure whether you have any metal objects or fragments inside you, you might need an X-ray before your MRI scan to check. Having something metallic in your body doesn’t necessarily mean you can’t have an MRI scan. But your radiographer does need to know so a safe decision can be made. 

    Before you go into the scanning room, you’ll probably be asked to undress down to your underwear, and put on a hospital gown. You should take off any clothes that contain metal, for example zips, clasps, metallic threads or underwiring (in bras). You’ll also need to remove any jewellery (including piercings) or metal objects such as hairclips, your watch or dentures with metal parts. You should even remove any nail polish which contains metallic glitter. Don't take any electronic or metal items, such as your keys, mobile phone or credit cards, with you into the scanning room. You may be able to have a friend or relative stay with you during the scan. He or she will also have to leave any metal or electronic items behind and complete and sign a safety questionnaire. 

    Young children having an MRI may be offered a sedative or a general anaesthetic. This means they will be drowsy or asleep during the procedure, which will help them to lie still.

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  • Alternatives What are the alternatives to an MRI scan?

    Other investigations that produce images of the inside of your body include the following.

    These techniques have different uses and your doctor will recommend the test which they consider best for you.

  • The procedure What happens during an MRI scan?

    An MRI scan is a painless procedure which allows your doctor to see detailed images of the inside of your body. You will have the scan in a hospital, but you can usually go home the same day. 

    An MRI scan usually takes between 30 and 50 minutes. However, some scans may last for an hour to an hour and a half. You’ll be told beforehand how long your scan will take. 

    Your radiographer will ask you to lie on your back on a table, which slides inside a cylinder-shaped machine. They may use foam pads or straps to adjust your position and help you to stay still. Your radiographer will make sure that you are comfortable and any equipment around you is in a safe place. 

    Usually, the part of your body being scanned is placed in the middle of the scanner. The machine is open at either end so you won't be completely enclosed at any time. 

    Your radiographer will operate the scanner from behind a window and will be able to see and hear you during the scan. They’ll talk to you during the scan to reassure you and remind you to be as still as you can. You will be shown a buzzer to press if you need to talk to your radiographer. 

    It can take up to several minutes for each image to be taken, so it's important to lie very still and breathe gently. If you move, it could mean you’ll need to have parts of the scan repeated.

    Your radiographer may ask you to hold your breath at certain times during the scan. The MRI scanner makes loud knocking or clanging sounds while an image is being taken. Your radiographer will usually give you earplugs or headphones to wear, and you may be able to listen to music during your scan. Sometimes a special dye (contrast medium) is used to give more detailed pictures. This will be discussed with you before your scan. If you’re having this dye, it will be injected into a vein in your hand or arm. You may feel a warm sensation after the dye is injected, which lasts for a short time. A very small number of people may be allergic to the dye. Tell your radiographer before your scan if you have any allergies.

  • MRI scans

    At our Bupa Health Centres, we offer self-pay health services for a wide range of conditions, including MRI scans.

  • Aftercare What to expect afterwards

    You’ll usually be able to go home when you feel ready after your MRI scan. If you haven’t had a sedative you can go back to your normal routine immediately afterwards. 

    If you have had a sedative during the scan, it can take up to 24 hours to completely clear from your body. This means you shouldn’t drive, drink alcohol, operate machinery or make important decisions for 24 hours afterwards. If you're in any doubt about driving, contact your motor insurer so that you're aware of their recommendations, and always follow your doctor's advice. You will also need to arrange for someone to drive you home. Try to have a friend or relative stay with you for the first 24 hours after your scan. 

    A radiologist (a doctor who specialises in using imaging methods to diagnose medical conditions) will examine your MRI scans. The results will be sent to the doctor who requested your test.

  • Risks What are the risks?

    MRI scans are commonly performed and generally safe. However, in order to make an informed decision and give your consent, you need to be aware of the possible side-effects and the risk of complications of this procedure.

    Side-effects

    Side-effects are the unwanted but mostly temporary effects you may get from the test. You may feel slightly claustrophobic and uncomfortable from being inside the scanner. If you're worried about this, talk to your radiographer.

    Complications

    Complications are when problems occur during or after the procedure. Most people aren't affected. An MRI is a very safe test and there are no known complications or side-effects from the magnetic field at the strength used during the scan. 

    It's possible you may have an allergic reaction to the contrast medium used, although this is very unlikely. If you have any sweating, rash or difficulty breathing during the scan, tell your radiographer immediately. They will know what to do, and a doctor will be available to treat the allergic reaction. 

    The exact risks are specific to you and will differ for every person, so we haven't included statistics here. Ask your radiographer to explain how these risks apply to you.

  • FAQs FAQs

    Can I have an MRI scan if I have metal or gold fillings in my teeth or a titanium dental implant?

    Answer

    Tooth fillings and braces aren't affected by the magnetic field in an MRI scan. However, they may affect the quality of the images if you're having your head scanned.

    Explanation

    It's safe to have an MRI scan if you have tooth fillings or braces. However, these can affect the images produced during the scan.

    If you have any fillings, dental implants or braces, let your radiographer know about them before your scan. If your dental implants are easily removable (for example, some braces can be taken out and put back in) your radiographer may ask you to remove them for the scan.

    I'm having an MRI scan but I'm scared of enclosed spaces – what should I do?

    Answer

    If you're anxious about being in an enclosed space, tell your radiographer before having the scan. There are several things that can be done to make the scan easier for you.

    Explanation

    If you have claustrophobia, or think you may get anxious inside the scanning machine, contact the radiography department where your scan will take place. You should do this when your appointment comes through rather than waiting until the day of the scan. This allows your radiographer enough time to make arrangements to help you during the scan. 

    MRI scanners are open at either end so you won't be completely enclosed at any time. 

    Your radiographer will be able to see and hear you during the scan. If you feel worried during your scan, tell your radiographer straight away. You will be shown a buzzer to press if you need to talk to the radiographer. 

    There are several things that can make the scan more comfortable for you. Some hospitals play music to help you relax. And you may be able to have a friend or relative sit with you during your scan. If so, they’ll also have to remove all their metal items. 

    If you're very anxious, you may be offered a sedative to help you relax during the scan. If you have a sedative, you’ll need to arrange for someone to drive you home. You should try to have a friend or relative stay with you for the first 24 hours after the scan. If your claustrophobia is severe, it may be possible to have the scan performed in a special type of scanner called an 'open' scanner. This is less enclosed than a conventional machine. However, these aren’t routinely available on the NHS. Availability will depend on the area where you live.

    What can an MRI scan be used for?

    Answer

    MRI scanners can be used to look at almost any part of your body and the results can help your doctor to diagnose or monitor your condition.

    Explanation

    Magnetic resonance imaging (MRI) can show a lot of detail in many different types of body tissues. It produces images that show differences between healthy and unhealthy tissues. It’s particularly good at looking at soft tissues, such as breast tissue and organs such as your brain, liver and heart. MRI scanning can also be used to examine your blood vessels, nerves, muscles and bones. 

    MRI can also be used to diagnose or monitor: 

    For some parts of your body and for some types of tissue, an MRI can produce clearer results than a CT scan. In other circumstances, a CT scan will be more suitable. Your doctor will know which type of scan is best for you.

  • Resources Resources

    Further information

    Sources

    • Kumar, P, Clark, M. Clinical medicine. 8th ed. Edinburgh: Saunders; 2012
    • Safety guidelines for magnetic resonance imaging equipment in clinical use. Medicines and Healthcare Products Regulatory Agency (MHRA), 2014. www.mhra.gov.uk
    • Magnetic resonance imaging. PatientPlus. Patient.co.uk/patientplus.asp, published 25 January 2013
    • Magnetic resonance imaging. Merck. www.merckmanuals.com, published August 2013
    • Magnetic resonance imaging (MRI). RadiologyInfo.org. www.radiologyinfo.org, published 12 February 2014
    • Patient safety - magnetic resonance imaging (MRI). RadiologyInfo.org. www.radiologyinfo.org, published 13 June 2013
    • MRI scans. Brain & Spine Foundation. www.brainandspine.org.uk, published July 2013
    • MRI scans. British Heart Foundation. www.bhf.org.uk, accessed 25 November 2014
    • MRI scan. Cancer Research UK. www.cancerresearchuk.org, Published 13 August 2013
    • MRI (Magnetic Resonance Imaging). U.S. Food and Drug Administration (FDA). www.fda.gov, published 4 June 2014
    • Anaesthesia explained – third edition. The Royal College of Anaesthetists, 2008. www.rcoa.ac.uk
    • Anesthesia. RadiologyInfo.org. www.radiologyinfo.org, reviewed 7 October 2014
    • NHS imaging and radiodiagnostic activity in England: 2012/13 release. NHS England, 2013. www.england.nhs.uk 
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    Reviewed by Pippa Coulter, Bupa Health Content Team, February 2015. 

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