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MRI scan

An MRI scan creates pictures using magnetism and radio waves. 

MRI stands for magnetic resonance imaging. It produces pictures from angles all around the body and shows up soft tissues very clearly.

Why you might have it

MRI can be used on most areas of the body. For some parts of the body and for some types of tissues, it can produce clearer results than a CT scan.

An MRI scan can be used to:

  • find a tumour
  • stage a cancer, to find out how big it is and whether it has spread
  • measure blood flow

You might have an injection of a special dye before the scan to help make the pictures clearer.

MRI is particularly good for some types of:

  • brain tumours
  • primary bone tumours
  • soft tissue sarcomas
  • tumours affecting the spinal cord

MRI instead of CT scans

In some situations, your doctor may suggest MRI if a CT scan hasn't been able to give all the information they need.

In some early cancers, such as cervix or bladder cancer, MRI is better than CT at showing how deeply the tumour has grown into body tissues. It can be particularly useful for showing whether the tissue left behind after treatment is cancer or not.

Preparing for your MRI scan

Before you go to your appointment, or when you arrive, you fill in a safety checklist. This asks about:

  • any operations you’ve had
  • whether you have any metal implants or other metals in your body

An MRI scan uses strong magnetism which could affect any metal in your body. This includes:

  • pacemakers or an implantable defibrillator (to treat abnormal heart rhythms)
  • surgical clips, pins or plates
  • cochlear implants (for deafness)
  • metal fragments anywhere in your body – for example from an injury

You can still have an MRI scan if you have some metals in your body, but your doctor and radiographer decide if it’s safe for you. Tell the scanner staff about any metals in your body.

Some people feel claustrophobic or closed in when they’re having an MRI scan. Contact the department before your test if you’re likely to feel like this. The hospital staff can take extra care to make sure you’re comfortable and that you understand what’s going on. Your doctor can give you medicine to help you relax if you need to.

Tell the department staff beforehand if you think you’re pregnant. An MRI is generally safe during pregnancy. But as a precaution, you usually won’t have one during the first 3 months of your pregnancy.

What to expect

When you arrive at the scan department

The radiographer might ask you to change into a hospital gown. You may not have to undress if your clothing doesn’t have any metal, such as zips or clips.

You have to:

  • remove any jewellery, including body piercings and your watch
  • remove your hair clips
  • empty your pockets of coins and keys

In the scanning room

Your radiographer takes you into the scanning room. The MRI machine is large and shaped like a doughnut.

MRI scan

It’s safe to take a relative or friend into the scanning room with you. But check with the department staff first. Your friend or relative has to remove any metal items.

You lie on a couch that can slide into the MRI machine. You usually lie down on your back.

You might have an injection of a dye called contrast medium. This helps to show up your body’s organs more clearly. Some people are allergic to contrast medium, so your radiographer will ask about any medical conditions or allergies you have.

You have the injection through a small plastic tube (cannula) into a vein in your arm.  

Tell the radiographer if you feel unwell at any point during or after your scan.

Having your MRI scan

You need to lie as still as possible. The scan is painless but it can be uncomfortable to stay still.

Once you’re in the right position on the couch, the radiographer leaves the room. They can see you on a TV screen or through a window from the control room.  You can talk to each other through an intercom.

The couch moves through the MRI scanner. It takes pictures as you move through it.

During the scan

The scanner makes a very loud clanging sound throughout the scan. You’ll wear earphones or headphones to protect your hearing. You can also listen to music. Keeping your eyes closed can help.

Your radiographer might ask you to hold your breath at times. Tell them if you are getting stiff and need to move.

This 1 minute video shows you what happens when you have an MRI scan.

After your scan

When the scan is over, your radiographer comes back into the room and lowers the couch so you can get up.

You might stay in the department for about 15 minutes so staff can make sure you’re OK. If you had a cannula, your radiographer removes the tube from the vein in your arm.

You should then be able to go home or back to work and also eat and drink normally.

Getting your results

You should get your results within 1 or 2 weeks. 

Waiting for results can make you anxious. Ask your doctor or nurse how long it will take to get them. Contact the doctor who arranged the test if you haven’t heard anything after a couple of weeks.

You might have contact details for a specialist nurse and you can contact them for information if you need to. It may help to talk to a close friend or relative about how you feel.

For information and support, you can contact the Cancer Research UK nurses on freephone 0808 800 4040. The lines are open from 9am to 5pm, Monday to Friday.

Possible risks

An MRI is very safe and doesn’t use radiation. Some people can’t have an MRI but the checklist picks this up beforehand.

The contrast medium injection can cause side effects. But these are usually mild and last for a short time.

They include:

  • feeling or being sick
  • a skin rash
  • a headache
  • dizziness

An allergic reaction to the contrast medium injection is rare. This most often starts with feeling weak, sweating and difficulty breathing. Tell your radiographer straight away if you feel unwell so they can give you medicine.

There is a risk that the contrast medium will leak outside the vein. This can cause swelling and pain in your arm but it’s rare. Tell your radiographer if you have any swelling or pain. Let your GP know if it doesn’t get better or starts to get worse when you’re at home.

Tell the department staff beforehand if you think you’re pregnant. An MRI is generally safe during pregnancy. But as a precaution, you usually won’t have one during the first 3 months of your pregnancy.

More information

We have more information on tests, treatment and support if you have been diagnosed with cancer.

Last reviewed: 
25 Apr 2015
  • The Royal Marsden Manual of Clinical Nursing Procedures, 9th Professional Edition

    L Dougherty and S Lister (Editors)

    Royal Marsden Manual Series, Wiley-Blackwell, 2015

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