What is magnetic resonance imaging (MRI)?

Magnetic resonance imaging (MRI) is a scanning procedure that uses strong magnets and radiofrequency pulses to generate signals from the body. These signals are detected by a radio antenna and processed by a computer to create images (or pictures) of the inside of your body.

The MRI scanner is generally shaped like a large, covered box with a tunnel passing through it. A table, on which you lie, slides into the tunnel. Both ends of the scanner are open and will not close. The tunnel has lights in it and sometimes a mirror. Some of the MRI scanners have wider tunnels or are partially open (more like a ‘C’, rather than an ‘O’).

How do I prepare for a MRI?

To ensure it is safe for you to have an MRI, you will be required to complete a safety questionnaire. Sometimes a questionnaire is mailed to you that you will need to complete and take with you to the appointment. If a friend or relative will be in the scanning room with you, they will also need to complete a safety questionnaire.

If you have a pacemaker or other implants, it is important to tell the radiology practice before having the scan. An alternative test might need to be arranged.

Objects in your body that can cause particular harm or be damaged include: pacemakers, aneurysm clips, heart valve replacements, neurostimulators, cochlear implants, metal fragments in the eye, metal foreign bodies, magnetic dental implants and drug infusion pumps. Some of these implants, particularly more recent devices, might be safe to go into the MRI scanner, but have to be accurately identified for the scan to proceed.

You will not be able to take anything with you into the scan room, and there are usually lockers available. It is easier if you leave objects such as watches, jewellery, mobile phones, belts, safety pins, hairpins and credit cards at home.

If you are pregnant, please discuss this with your doctor and tell the radiology practice before having the scan.

If you are claustrophobic (a fear of small or enclosed spaces) and think you might not be able to proceed with the scan, advise your doctor or the MRI facility when making your appointment. Sedative (calming) medication can be given. If this happens, you will not be able to leave the facility until you are fully awake and someone else will need to drive you home.

There is music attached to the MRI scanner. You can take ask to listen to anything you would like while you are having the scan.

How long does an MRI take?

The scan can take between 10 minutes to over an hour to complete. This depends on the part of the body being imaged and what type of MRI is required to show the information. Before the scan begins, the radiographer will tell you how long the scan takes, so you know what to expect. Occasionally, you might need to return for delayed scans, usually after 1 or 2 hours, mostly with scanning of the liver.