MRI scan

An MRI (magnetic resonance imaging) scan uses a strong magnet and radio waves to make detailed pictures of the inside of the body. It is especially good at showing soft parts such as the brain, spinal cord, nerves, muscles, ligaments and tendons. You lie on a bed that slides into a large tube-shaped scanner. Sometimes a contrast dye is given into a vein to make parts show up more clearly.

A doctor may ask for an MRI to find the cause of symptoms, to look closely at the brain, spine or a joint such as the knee, or to follow a condition. A brain scan can help find the cause of a stroke, bleeding, infection, a tumour, or problems with thinking and memory such as dementia. A spine scan is used for back pain that does not improve, leg weakness or numbness, and trouble controlling the bladder.

Answer the safety form fully, because the magnet can pull on metal and affect some devices.

1. The radiographer goes through your safety form with you. You remove metal items, and if dye is needed it goes into a vein in your arm.
2. You lie on a padded bed and are given earplugs or headphones, because the scanner is loud.
3. The bed slides into the scanner. The radiographer works from another room, and you can speak to them through an intercom at any time.
4. You lie still, because movement blurs the pictures, and may be asked to hold your breath for short spells.

The scan often takes 15 to 60 minutes, and sometimes longer.

You can usually eat, drink and carry on as normal. If you had dye, you may be asked to wait up to 30 minutes to check for a reaction. After a relaxing medicine, someone should take you home and you should not drive for 24 hours. A radiologist writes to the doctor who asked for the scan, usually within 1 to 2 weeks.

MRI uses no radiation, and no harm from the magnetic fields or radio waves has been reported. The main risks come from the magnet, which can affect pacemakers and some other implants and can move metal in the body.

Dye may cause a small bruise, sickness or a headache. Allergic reactions are rare, so tell staff at once if you feel unwell. Some dyes can cause a rare serious reaction in people with severe kidney failure, so tell the team about kidney disease. If you are pregnant, tell the team before the scan.

The doctor who asked for the scan explains the result and may arrange a follow-up visit.

What an MRI cannot do: pictures blur if you move, so people who cannot lie still, such as young children, may need medicine or anaesthesia. A CT scan takes less time and is often chosen when time matters.