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MRI (magnetic resonance imaging)

Whakaahua orooro autō

Magnetic resonance imaging (MRI) is a type of scan that produces three-dimensional images of the inside of your body. It uses strong magnets and radio waves to generate signals from your body. These signals are then picked up by a radio antenna and processed by a computer to produce images.

An MRI scan can be done to help diagnose conditions, plan treatments and check how effective previous treatment has been.

The MRI takes 15 to 90 minutes depending on which part of your body is being scanned.

Before your scan

It's important to tell the radiology staff about any metal you have in your body, including possible metal fragments in your eye and metal foreign bodies. Objects that have been implanted in your body need to be discussed ahead of the MRI scan as they may cause harm or be damaged. These include pacemakers, aneurysm clips, heart valve replacements, neurostimulators, cochlear implants, magnetic dental implants and drug infusion pumps.

If you have a fear of small or enclosed spaces (claustrophobia) and think you might not be able to cope with the scan, talk to your doctor or the radiology service when you receive your appointment letter. You may be given some techniques to help keep you calm or medicine to help you relax (a sedative).

During your scan

You'll be asked to lie on a motorised table. The table will slide through the opening of the scanner, which is shaped like a large tunnel with a ring. The scanner is very noisy as it works, so you'll be given ear plugs and headphones to wear.

The person doing the scan will be able to see and hear you at all times and you'll be able to communicate with them through an intercom. It's important to stay as still as you can throughout the scan.

Sometimes, you'll need an injection of contrast dye to make the scan easier to read.

After your Scan

A specialist doctor (radiologist) will view the images and write a report about what the scan shows. They will send their report to the health professional who asked for the test, who will then discuss the test results with you during a follow-up appointment, over the phone or by email or text message.

Risks of the scan

MRI is very safe and uses no ionised radiation.

If you need a contrast dye injection, a small plastic tube will be put in a vein in your arm. There is a small chance of an allergic reaction. This is usually mild, but if you have a more severe reaction, the MRI staff will treat it.

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Written by HealthInfo clinical advisers. Last reviewed December 2022.

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