Most MRI scans don't need any special preparation. However, if you're having a scan of your abdomen (tummy) or your pelvis, you may be asked to drink extra fluids before the scan. This is to help your stomach and bowel show up better on the scan. Your radiographer will tell you if you should drink 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 tell the radiographer before the day of your scan. You can have a sedative to help you relax during the scan, but this will need to be arranged in advance. If your claustrophobia is severe, it may be possible to have the scan performed in a special type of scanner called an 'open' scanner which is less enclosed than a conventional machine. For more information see our frequently asked question.
Young children may also be offered a sedative or a general anaesthetic. This means they will be drowsy or asleep during the procedure.
An MRI scan is usually done in the out-patient department of your hospital. This means that you have the scan and go home the same day.
At the hospital, your radiographer will ask you to complete and sign a safety questionnaire.
You will probably be asked to take off your outer clothes 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). Also remove any jewellery or metal objects such as hairclips, your watch or dentures with metal parts. Don't take any electronic or metal items, such as your keys, mobile phone or credit cards, with you into the scanning room.
You can ask for a friend or relative to 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.
Other investigations that produce images of the inside of your body include the following.
- X-ray. This uses radiation to produce an image.
- Ultrasound. This uses sound waves to produce an image.
- Computerised tomography (CT) scan. This is a test that uses X-ray equipment and computer software to create images.
Talk to your doctor about which procedures are most suitable for you.
An MRI scan usually takes between 20 and 40 minutes to complete. However, some scans may last for an hour to an hour and a half. You will 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. He or she may use pillows or straps to adjust your position and help you to stay still. An open frame that contains a radio aerial may need to be placed around the part of your body being scanned to help improve image quality.
Usually, the part of your body being scanned is placed in the middle of the scanner. The machine is open ended 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. He or she will talk to you during the scan and remind you to be still. You will be given a call button to hold during the scan, and you can press this button to talk to your radiographer in an emergency. He or she will let you know what is happening during the scan and what you need to do before and during the examination.
The MRI scanner makes loud knocking or buzzing sounds throughout the scan. Your radiographer will usually give you earplugs or headphones to wear, and you can listen to music during the scan. You may be able to bring your own choice of music with you.
It can take several minutes for each image to be taken, so it's important to lie very still and breathe gently. Any movement can blur the scan. Your radiographer may ask you to hold your breath at certain times during the scan.
Sometimes a special dye (contrast medium) is used during the scan to produce more detailed images. If you have kidney problems, tell your radiographer when booking the MRI scan appointment. The dye is 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.
You will usually be able to go home when you feel ready.
If you have a sedative during the scan, it can temporarily affect your co-ordination and reasoning skills, so you must not drive, drink alcohol, operate machinery or sign legal documents 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.
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 are the unwanted but mostly temporary effects you may get after having 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 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 used during the scan.
It's possible to have an allergic reaction to the contrast medium used, although this is very unlikely. If you have any itching or shortness of breath during the scan, tell your radiographer immediately. Medicines are 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.
Can I have an MRI scan if I have metal or gold fillings in my teeth or a titanium dental implant?
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.
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?
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.
If you have claustrophobia, or think you may get anxious inside the scanning machine, contact the radiography department where your scan will take place the day before. Getting in touch before your appointment allows your radiographer enough time to make arrangements to help you during the scan.
MRI scanners are open ended so you won't be completely enclosed at any time. The newer scanners are much shorter and wider than older ones, have a light inside and a slight breeze flowing through them.
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 given a call button to hold during the scan, which you can press to talk to the radiographer. Some radiography departments may be able to supply you with special viewing glasses that allow you to see out of the scanner and show the rest of the room.
There are several things that can make the scan more comfortable for you. Some hospitals play music to help you relax or you may be able to take some music with you for them to play.
If you're very anxious, you may be offered a sedative to help you relax during the scan. If you have a sedative, you will 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.
What can an MRI scan be used for?
MRI can be used to look at almost any part of your body and it can help your doctor to diagnose or monitor your condition.
Magnetic resonance imaging (MRI) can show a lot of detail in soft tissues, such as breast tissue, organs such as your brain, liver and heart and your blood vessels and nerves. MRI scanning is particularly good at showing diseases or injuries of the spine, head and neck and muscles and bones.
MRI can also be used to diagnose or monitor:
- conditions that affect the brain, for example, dementia, stroke, multiple sclerosis and meningitis
- heart conditions, for example, valve problems or narrowing of your blood vessels
- liver or kidney disease
- conditions or injuries that affect your bones and joints, for example, arthritis or sports injuries
- bowel disease
For some parts of your body and for some types of tissues, an MRI can produce clearer results than a CT scan. In other circumstances a CT scan will give better images. Your doctor will know which type of scan is best for you.
- Royal College of Radiologists
- MRI of the body. American College of Radiology and the Radiological Society of North America. www.radiologyinfo.org, published 24 April 2012
- The MRI machine. Royal College of Radiologists. www.goingfora.com, accessed 22 July 2012
- MRI scan. Cancer Research UK. www.cancerresearchuk.org, published 16 November 2011
- Magnetic resonance imaging. Merck Manuals. www.merckmanuals.com, published April 2008
- Magnetic resonance imaging: information for patients. International Society of Magnetic Resonance in Medicine. www.ismrm.org, accessed 22 July 2012
- Royal College of Radiologists
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