MRI scan

  • MRI (magnetic resonance imaging) is a type of scan that uses magnetism and radio waves to take pictures of inside the body.
  • The scan takes between 15 and 90 minutes.
  • You might have one to find out whether you have cancer and if you do to measure how big it is and whether it has spread. You might also have one to see how well treatment is working.
  • It is a safe test. If you have an injection of contrast dye it can cause a headache, dizziness or a warm flushed feeling

An MRI is a type of scan that creates pictures using magnetism and radio waves. MRI scans produce pictures from angles all around the body and shows up soft tissues very clearly. 

MRI stands for magnetic resonance imaging.

They take between 15 and 90 minutes. 

Why do I need an MRI scan?

An MRI scan can be used to look at 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 can be used to:

  • find a tumour
  • find out how big it is and whether it has spread (stage a cancer)
  • measure blood flow
  • to check how well treatment is working

You might have an injection of a special dye (contrast medium) before the scan. This is to help make the pictures clearer.

MRI scans are particularly good for:

  • brain tumours
  • primary bone tumours
  • soft tissue sarcomas
  • tumours affecting the spinal cord
  • tumours in the pelvic organs (prostate, bladder, uterus and ovaries)

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 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 metal 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, dental fillings and bridges 

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

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.

Tell the department staff beforehand if you think you’re pregnant. 

What to expect

When you arrive at the scanning department, the radiographer might ask you to change into a hospital gown. You might 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

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 will also need to remove any metal they have on them.

In the scanning room

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

Photograph of an MRI scanner

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

You might have an injection of a dye (contrast medium) through a small plastic tube (cannula) into a vein in your arm. This helps to show up your body’s organs more clearly. Some people are allergic to the dye, so your radiographer will check first about any medical conditions or allergies you have.

After the dye injection you may:

  • feel sick
  • have a headache
  • feel warm or flushed
  • have a metallic taste in your mouth
  • feel a little dizzy

These effects are usually mild and last for a short time. Tell your radiographer if you feel unwell at any point during or after your scan.

Having the MRI scan

You need to lie as still as possible. The scan is painless but it can be uncomfortable to stay still. Tell the radiographer if you're getting stiff and need to move. 

The scan can take between 15 and 90 minutes. It depends on the area that they need to scan and how many images they need. 

Once you’re in the right position on the couch, your radiographer leaves the room. They can see you on a TV screen or through a window at all times from the control room. You can talk to each other during the scan, usually through an intercom. You will have a button you can press if you want them to stop the scan immediately if you feel claustrophobic.

The couch moves through the MRI scanner. It takes pictures as you move through it. Your radiographer might ask you to hold your breath at times. 

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

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

After your MRI scan

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

You usually stay in the department for about 15 minutes after your scan if you've had the dye. This is in case it makes you feel unwell.  

Your radiographer removes the cannula from the vein in your arm before you leave.

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

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. Your doctor and radiographer make sure the benefits of having the test outweigh any possible risks.

Some of the possible risks include: 

Bruising and swelling

You might get a small bruise around the area where they put the needle in for the cannula. 

There's 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.

Allergic reaction 

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 to control the reaction.

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 who you can contact for information if you need to. It may help to talk to a close friend or relative about how you feel. You may want them to go with you to get the results for support.

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

More information

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

  • The Royal Marsden Manual of Clinical and Cancer Nursing Procedures (10th Edition)
    S Lister, J Hofland and H Grafton (Editors)
    Wiley-Blackwell, 2020

  • Safety Guidelines for Magnetic Resonance Imaging Equipment in Clinical Use
    Published by the Medicines and Healthcare products Regulatory Agency, February 2021

  • Guidance on gadolinium-based contrast agent administration to adult patients
    The Royal College of Radiologists, April 2019

  • Safety in Magnetic Resonance Imaging
    The Society and College of Radiographers and the British Association of MR Radiographers, February 2019

  • Iodinated Contrast Media Guideline
    The Royal Australian and New Zealand College of Radiologists, March 2018

  • The information on this page is based on literature searches and specialist checking. We used many references and there are too many to list here. Please contact patientinformation@cancer.org.uk with details of the particular issue you are interested in if you need additional references for this information.

Last reviewed: 
31 Oct 2022
Next review due: 
31 Oct 2025

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