his is a relatively new and special examination of the human body, which uses electromagnetic waves and sophisticated computers to produce images of the internal organs of the body. For this to be possible, the patient will be placed within the bore of a large magnet, which produces a magnetic field several thousand times stronger than that of the earth.  

Radio waves are used to produce images of the internal structure of the body. This is an excellent non-invasive way of looking into the human body without the need for needles, catheters or operations. Structures as small as one millimeter in diameter can be visualized. Excellent characterization of soft tissue is obtained. It is possible to look at the major blood vessels of the body without injection of contrast medium. The structure and function of the heart can also be assessed. The images that are obtained will be viewed by the radiologist to look for evidence of disease. There is no radiation involved and there is no known risk to children or adults.  

There are several different types of MR scanners. Those that use a stronger magnet generally produce better images. The MR scanner comprises a magnet with a hollow center called the bore. The patient will be placed within the bore of the magnet. The bore has a variable diameter some of which may be as small as 60 cm. The length of the bore is approximately 1.5m. However there are MR scanners which have an open magnet, where there is no bore. This would be suitable for patients who may not be able to tolerate being in the closed space of the narrow MR scanners. Interventional procedures under MR guidance is also possible using the open magnet MR scanner.

The majority of patients can undergo an MRI scan. It is safe for women who are more than four months pregnant to undergo this examination. Those who are less than four months pregnant should discuss the need for the examination with their doctor and the radiologist who will be supervising the examination.  

Patients weighing more than 140 kilograms cannot be scanned. MRI can cause serious injury and even death in those with metal embedded in their bodies. Patients with the following objects inside the body generally cannot undergo an MRI examination:

• Pacemaker

• Metallic foreign bodies

• Metallic implants

• Heart valves

• Surgical staples

• Shrapnel

• Aneurysm clips

• Vascular coils and filters

Depending on which part of the body is to be examined, the patient may be required not to drink or eat for at least six hours before the examination. At the time of examination, female patients should not use any facial make-up as this may interfere with the image. The patient will be required to change into a hospital gown and remove all removable metallic objects (e.g. jewellery, belt, buckles, pins etc) before entering the MR scan room. After interviewing the patient, a radiographer will position the patient on the scanner bed.

Close relatives are usually allowed to be in the scanner room with the patients during the examination, if it is required. Earplugs are supplied to patients, as there will be a loud knocking noise during the examination. This scanner bed will then be moved into the magnet tunnel. It is very important for the patient to lie still during the examination. Sedation may be required for children and for patients who are irritable or agitated. In a few MRI units, scanning is done under general anaesthesia in children.

It will be possible to communicate with the radiographer via an intercom throughout the procedure. The radiographer will be able to observe the patient through a glass window from the control room or through a TV monitor via a camera positioned in the scanner. The radiologist may decide to give the patient an injection of a special dye for MRI scanning. This may sometimes cause a feeling of warmth for a short while. The total duration of the examination varies from 30-90 minutes depending on the part of the body being examined. Generally, there are no side effects from the examination.

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Last Updated:
Thursday, 21 August, 2003