MRI Scan

What is an MRI scan?

MRI stands for magnetic resonance imaging. An MRI scan uses a strong magnetic field and radio waves to create pictures on a computer of tissues, organs and other structures inside your body.

How does an MRI scan work?

Your body contains millions of hydrogen atoms. When you are in an MRI scanner:

• A strong magnetic field aligns particles called protons which are within the hydrogen atoms. All the protons line up in parallel to the magnetic field like tiny magnets. (Normally the millions of protons all lie in random directions.)
• Then, short bursts of radio waves are sent from the scanner into your body. The radio waves knock the protons from their position.
• When the burst of radio waves stops, the protons realign back into place. As they do so they emit radio signals. The protons in different tissues of the body realign at different speeds. Therefore, the signal emitted from different body tissues varies. So, for example, softer tissues can be distinguished from harder tissues on the basis of the signals sent.
• These signals are detected by a receiving device in the scanner.
• The receiving device transmits the signals to a computer. The computer creates a picture based on the radio signals emitted from the body.

What does an MRI scan involve?

The MRI scanner is like a tunnel about 1.5 meters long surrounded by a large circular magnet. You lie on a couch which then slides into the scanner. A 'receiving device', like an ariel, is placed behind, or around, the part of the body being examined. This detects the tiny radio signals emitted from your body. When each 'picture' is being taken you need to keep still for a few minutes otherwise the scan picture may be blurred.

The scan itself is painless. The whole procedure can take 15-40 minutes. It may be a little uncomfortable lying still on the couch for this time. Small children may need a general anaesthetic to keep them still long enough for the pictures to be taken. In some cases an injection of a special contrast dye is given into the bloodstream via a vein on the arm. This helps to give clearer pictures of certain tissues or organs being examined.

The radiographer sits in the control room next to the scanner and observes through the window. However, you can talk to them, usually via an intercom, and you will be observed at all times on a monitor.

The scanner is noisy so you will be given some headphones or earplugs to protect your ears from the noise. Quite often you can listen to the radio through the headphones or bring a CD to listen to.

What is an MRI scan used for?

An MRI scan can create clear pictures of most parts of the body. So it is useful for all sorts of reasons where other tests (such as X-rays) do not give enough information required. It is commonly used to get detailed pictures of the brain and spinal cord, to detect abnormalities and tumours. Even torn ligaments around joints can be detected by an MRI scan. So, it is being used more and more following sports injuries.

What preparation do I need to do before an MRI scan?

Usually very little. But there are certain safety procedures as you will be inside a strong magnet. You have to fill in a safety questionnaire (when you attend) that asks about things that may contain metal such as pacemakers, hearing aids, etc. Try not to wear anything with metal in. Fixed bits of metal in your body such as an artificial hip or screws used to fix fractures are usually fine after eight weeks, but you should tell the radiographer if you have any metal inside your body. (There will be a section on the safety questionnaire about this for you to fill in.)

Are there any possible complications?

MRI scans are painless and safe. Unlike X-rays and some other imaging tests, an MRI scan does not use radiation. However:

• Rarely, some people have reactions to the contrast dye which is sometimes used.
• Pregnant women are usually advised not to have an MRI scan unless it is urgent. Although the scan is thought to be safe, the long-term effects of strong magnetic fields on a developing baby are not yet known.

What can I expect after the scan?

There are no after-effects from the scan. You can return to your normal activities as soon as the scan is over.

The pictures from the scan are studied by an X-ray doctor (a radiologist) who sends a report to the doctor who requested the scan.