MRI Scan - Tests & Treatments - NHS Inform

About an MRI scan

Magnetic resonance imaging (MRI) is a type of scan that uses strong magnetic fields and radio waves to produce detailed images of the inside of the body.

An MRI scanner is a large tube that contains powerful magnets. You lie inside the tube during the scan.

An MRI scan can be used to examine any part of the body.

The results of an MRI scan can be used to:

• help diagnose conditions
• plan treatments
• assess how effective previous treatment has been

Before an MRI scan

On the day of your MRI scan, you should be able to eat, drink and take any medication as usual, unless you’re advised otherwise.

In some cases, you may be asked not to eat or drink anything for up to 4 hours before the scan. Other patients may be asked to drink quite a large amount of water beforehand. This depends on the area being scanned.

When you arrive for your scan, you’ll be asked to fill in and sign a questionnaire about your health and medical history. This helps to ensure that it’s safe for you to have the scan.

As the MRI scanner uses strong magnetic fields, it’s important to remove any metal objects from your body. These include:

• watches
• jewellery, like earrings and necklaces
• piercings, like ear, nipple and nose rings
• dentures (false teeth)
• hearing aids
• wigs (some wigs contain traces of metal)
• hairpins
• medicine patches (like nicotine or hormone patches)
• glucose monitors
• tethered or patch insulin pumps

You should avoid bringing valuables along with you to your MRI scan. However, any valuables you do bring can usually be stored in a secure locker.

Depending on which part of your body is being scanned, you may need to wear a hospital gown during the procedure.

If you don’t need to wear a gown, you should wear clothes without metal zips, fasteners, buttons, underwire (bras), belts or buckles.

Is an MRI scan safe?

An MRI scan is a painless and safe procedure. Extensive research has been carried out into whether the magnetic fields and radio waves used during MRI scans may pose a risk to the human body. No evidence has been found to suggest there’s a risk, which means MRI scans are one of the safest medical procedures available.

Some patients occasionally experience a tingling sensation or feel hot from being in the MRI scanner. These effects only last a short while and should ease as soon as the scan is over.

You’re given a squeeze alarm which can alert the Radiographers if you have any concerns during your scan.

MRI scans may not be recommended for patients with certain implants or foreign bodies. If you have any metal in your body, you should tell the person referring you for the scan,. This can then be looked into before your scan.

Read more about who can and can’t have an MRI scan.

Contrast agents

Some MRI scans involve having an injection of a contrast agent. This makes certain tissues and blood vessels show up more clearly and in greater detail.

Sometimes the contrast agent can cause side effects, like:

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

These side effects are usually mild and don’t last very long.

It’s also possible for contrast agents to cause tissue and organ damage in people with severe kidney disease. You may be given a blood test to determine how well your kidneys are functioning and whether it’s safe to go ahead with the scan.

You should let the staff know if you have a history of allergic reactions or any blood clotting problems before having the injection.

Anaesthesia and sedatives

An MRI scan is a painless procedure, so anaesthesia (painkilling medication) isn’t usually needed.

If you’re claustrophobic, you can ask for a mild sedative to help you relax. You should ask your GP or consultant well before having the scan.

If you decide to have a sedative during the scan, you’ll need to arrange for a friend or family member to drive you home afterwards, as you won’t be able to drive for 24 hours.

Babies and young children may be given a general anaesthetic before having an MRI scan. This is because it’s very important to stay still during the scan, which babies and young children are often unable to do when they’re awake.