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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

5-minute read

What is an MRI scan?

A magnetic resonance imaging (MRI) scan takes detailed pictures of the inside of the body. It can show up problems in the soft tissues without the need for surgery. It is also useful for planning some treatments of the same areas.

When you have an MRI, you usually lie on a table that slides through a tunnel in the middle of the MRI scanner. The 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 detailed pictures.

The benefits of an MRI are that it produces very detailed pictures, does not use x-ray radiation, and is painless.

When is an MRI scan used?

An MRI is used to show certain problems, such as an injury, or in combination with other tests to diagnose a condition.

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

Is an MRI safe?

An MRI is a very safe procedure, but there are some things you should consider before the scan.

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 2 hours or more.

If you are afraid of small or enclosed spaces, make sure you tell the doctor first. It may be possible for you to have medication to keep you calm during the scan. Sometimes you will be able to take a CD or DVD into the scan with you to keep you occupied. Young children and babies may need a general anaesthetic to keep them still.

Some people cannot have an MRI, for example, people with a pacemaker or certain implants. This is because metal interacts with the magnet and can cause serious harm to the patient.

Make sure you tell the doctor who orders the scan and also the radiology practice if you have a:

  • pacemaker
  • aneurysm clip
  • heart valve replacement
  • neurostimulator
  • cochlear implant
  • metal fragments in the eye
  • metal foreign bodies
  • magnetic dental implant
  • drug infusion pump

If you have one of these implants, it may still be possible to have an MRI scan. But sometimes your doctor will need to order an alternative type of scan.

Make sure you do not wear any make up or hairspray when you have your MRI scan, as these may contain tiny metal particles that may interfere with the scan, heat up or even burn you.

Having an MRI is thought to be safe in pregnancy, apart from in early pregnancy, but discuss this with your doctor.

Where can I get an MRI scan?

MRIs are done in most public and private hospitals as well as in radiology practices.

The scan is conducted by a radiographer who is specially trained. The images are then shown to a radiologist, a specialist doctor who can interpret the findings and provide a report to your doctor.

What happens during an MRI scan?

Before the scan, you may be asked to fast (go without food). You will be asked about any metal in your body. If you might be pregnant, or have kidney problems, or do not like closed spaces, talk to the staff beforehand.

You will be asked to change into a gown and put your personal items in a safe locker. Depending on the scan, you might or might not need to be injected with dye to help the tissues show up.

You will then lie on a table and be given a buzzer to hold. When you press the button, you will be able to talk to the radiographer, who is in a different room. You will also be given earplugs or headphones to protect your ears, as the MRI scanner is very noisy.

Depending on the scan, you will have leads placed on your chest to monitor your heartbeat, a plastic tube attached to your finger to check your breathing and heartrate, or a needle inserted into a vein if any medication is needed during the scan.

The part of the body that is being scanned will be put into position and gently secured. Special coils are placed around it, usually in a pad or frame, to pick up signals from your body so the computer can create the images.

The table will then be moved in and out of the tunnel in the MRI scanner.

What does an MRI scan feel like?

An MRI scan is painless. Some people may feel warm during the scan. If this happens, make sure you tell the radiographer.

Are there side effects or complications of an MRI scan?

There are no known side-effects of MRI, apart from problems with implants or objects that must not go in the scanner. After the scan, you will be able to carry on with your day as normal.

If you needed sedation or medication during the scan, you might experience side effects or feel drowsy. The staff will tell you what you need to do, and whether or not you should drive.

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

Are there alternatives to an MRI scan?

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

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Last reviewed: May 2021


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