What is an MRI?

MRI (magnetic resonance imaging) is the name given to a technique, which builds up pictures of an internal cross-section of the part of the body under investigation.

The large machine is about four feet long and the area of interest is positioned in the centre. It uses a magnetic field and radio waves, together with an advanced computer system. It builds up a series of images, each one showing a thin slice of the area being examined. These images are very detailed. They can show both bones and soft tissues in the body and provide a great deal of information. Using the computer, the ‘slices’ can be also be obtained in any direction.

MR images allow physicians to evaluate parts of the body and certain diseases that may not be assessed adequately with other imaging methods such as x-ray, ultrasound, or computed tomography (CT).

What happens during the MRI?

You will be taken into the MRI scan room and made comfortable lying on the couch. Pads and pillows may be used to help you stay still and maintain your position during imaging. You may be given a contrast medium (a dye), which helps to produce more detailed images. The contrast medium will be injected into a vein in your arm, which occasionally causes a warm feeling for a short while. If this is required you may need to have a blood test prior to your scan.

Are there any risks?

As far as is known at present, this is an extremely safe procedure. It does not involve the use of x-rays. You are placed in a very powerful magnetic field. If you have any small pieces of metal inside your body, you should inform the radiographer as in some cases you may not be able to have the examination. If you have a history of metal fragments in your eyes, you may need an x-ray done to prove there are no fragments remaining. If you have a pacemaker, metal heart valves or a metallic clip in your brain, there is a risk that these may be affected during an MRI scan, and a different examination will need to be arranged instead.

For female patients, if you are or might be pregnant, you must make sure the doctor referring you or a member of staff in the radiology department knows as soon as possible. MRI scans are not advisable in early pregnancy unless there are special circumstances.