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An MRI scanner uses strong magnetic fields and radio waves to take detailed pictures.

An MRI scanner uses strong magnetic fields and radio waves to take detailed pictures.
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MRI scan

2-minute read

A magnetic resonance imaging (MRI) scan takes detailed pictures of the inside of your body. It is useful for diagnosing tumours, joint or spinal injuries or diseases, soft tissue injuries or diseases of internal organs such as the brain or heart. It can show up problems in your veins and arteries without the need for surgery. It is also useful for planning some treatments of the same areas.

What is an MRI scan?

An MRI scanner uses strong magnetic fields and radio waves to generate signals from the body. These are picked up by a radio antenna and processed by a computer to create pictures of the soft tissue inside of your body.

The benefits include:

  • very detailed pictures
  • no X-ray radiation
  • no pain.

When is an MRI scan used?

An MRI scan can be used to examine the:

  • brain and spinal cord
  • bones and joints
  • breasts
  • heart and blood vessels
  • internal organs, such as the liver, womb or prostate gland.

MRI is generally used for investigation, diagnosis and planning of treatment of:

  • tumours
  • joint injury or disease
  • soft tissue injury
  • internal organ damage.

Things to consider

Having an MRI is thought to be safe in pregnancy, but discuss this with your doctor. You must lie still in a confined space, which some people find difficult. It can last as little as 10 minutes, but most are longer. An MRI scan can last as long as two hours or more.

People with certain implants such as a pacemaker and other devices cannot have an MRI scan. Metal interacts with the magnet and can cause serious harm.

The process of having an MRI scan

Preparing for the scan:

  • You may need to go without food beforehand (fast).
  • You might or might not need to be injected with dye to help the tissues show up.
  • Staff will ask about metal in your body, such as pacemakers and metal plates, screws or pins.
  • If you might be pregnant, or have kidney troubles, or do not like closed spaces, talk to the staff beforehand.

During the scan:

  • You lie on a bed that is moved in and out of a cylindrical tube. You won’t feel anything.
  • Radiological staff sit in a different room, but you can talk to them at all times.
  • The MRI scanner is very noisy. You can ask for headphones or earplugs.
  • Young children and babies may need a general anaesthetic to keep them still.

Side-effects and complications of an MRI scan

There are no known side-effects of MRI, aside from implants or objects that must not go in the scanner.

Complications may include:

  • physical harm if safety procedures regarding metal are not followed
  • allergic reaction to the contrast dye
  • worsening of kidney function after contrast dye.

MRI scan alternatives

Alternatives to an MRI scan include other imaging such as X-ray, CT scan or ultrasound.

Last reviewed: June 2017

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