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Magnetic Resonance Imaging (MRI) - What Does MRI Mean?
Magnetic resonance imaging (MRI) is a modern and accurate medical tool available to physicians for the sectional imaging of the inner body. This "magnetic view" provides physicians with a host of detailed information on the location, size and composition of the body tissue to be examined. This knowledge may be decisive in helping to establish a fast and accurate diagnosis.
MRI does not make use of X-ray. In fact, as the name indicates, the procedure is based on the magnetic properties of atoms which make up all matter - including the human body. In a strong magnetic field, such as the one produced by the MRI scanner, electrical signals are emitted by atomic nuclei in the body tissue. These signals are intercepted by a circular antenna surrounding the patient. Signal intensity varies according to tissue type. A computer assigns the signals to the corresponding points on the body areas under examination and transforms them into an image on a screen.
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Preparatory Measures
Clothing need not to be removed, as is the case in most X-ray examinations, however, patients are asked to remove all objects which may interfere with the imaging process, especially those containing metal. This includes not only ear-rings, brooches, necklaces, wrist watches, but also ball-point pens and keys. Patients should also take out any removable dental plates and inform the physician if they have any other metallic implants or foreign objects including:
heart pace-maker
artificial heart valve
vascular prosthesis ("stent")
artificial limb
metallic nail or plate
metal splinter or shrapnel
intra-uterine device (for birth control/contraception)
The examining physician should be informed if you are pregnant.
For the examination, patients are assisted onto a padded recliner in the centre of the MRI scanner. It is important they find a comfortable position right from the start and remain as calm and quiet as possible during the actual examination as any physical movement can interfere with the accuracy of the measurements or distort the test results.
Patients can help by:
not drinking any coffee or tea on the day of the examination.
not using any make-up or hairspray as this could interfere with the imaging.
wearing loose fitting clothes without zips or metal fasteners.
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A Word about Safety
Since magnetic resonance imaging does not involve the use of X-rays, there is no need for the kind of precautionary measures necessary for X-ray examinations. According to current scientific knowledge, the magnetic field strength necessary to obtain accurate test results (up to 2 Tesla = 20,000 times the Earth's magnetic field) has no detrimental effect. In fact, in the past few years several million examinations have been performed without any known side effects arising - either during or after the examination. MRI examinations can generally not be performed in patients with a heart pace-maker.
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What Happens During the Examination?
During the examination patients lie in the centre of the tunnel-like opening of the MRI-scanner. This is neither dangerous nor painful. However, if patients don't like the 'closed in' feeling or suffer from claustrophobia, it may be helpful, on consulting the physician, to take a mild sedative.
Each MRI examination takes 5-15 minutes. At the time of the examination patients will hear a tapping noise. That's nothing to worry about, it's just the normal functioning of the MRI-scanner.
If several images need to be taken, the recliner will automatically be moved to the appropriate position. The patient should continue to remain as still as possible. Depending on the type of examination, the entire procedure could take up to 60 minutes.
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Using a Contrast Medium
In some cases a specially designed MRI contrast medium is injected to improve the image quality and enhance the reliability of the diagnosis. These contrast agents are fundamentally different from the iodine-based contrast agents used in X-ray examinations; they are extremely well-tolerated by patients.
During the entire examination patients are in the constant and direct care of specially trained personnel under the direction of a doctor.
If you have any questions about MRI or contrast media, your physician will be happy to discuss them with you.
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