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An MRI (magnetic resonance imaging) scan is a fairly new technique that has been used since the beginning of the 1980s. The MRI scanners use magnetic and radio waves, meaning that there is no exposure to X-rays or any other damaging forms of radiation.
The patient lies inside a large, cylinder shaped magnet. Radio waves 10,000 to 30,000 times stronger than the earth’s magnetic fields are then sent through the body. This affects the body's atoms, forcing the nuclei into a different position. |
As they move back into place they send out radio waves of their own. The scanner then picks up the signals and a computer turns them into a picture.
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What does an MRI scan show?
Using an MRI scanner it is possible to make pictures of almost all the tissue in the body. The tissue that has the least hydrogen atoms (such as Bones) shows up dark; tissue that has many hydrogen atoms (such as fatty tissue) looks much brighter. By changing the timing of the radio wave pulses it is possible to gain information about the different types of tissues that are present. An MRI scan is also able to provide clear pictures of parts of the Body that are surrounded by bone tissue, so the technique is useful when examining the brain and spinal cord.
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How does an MRI scan differ from a CT scan?
With an MRI scan it is possible to take pictures from almost every angle, whereas a CT scan only takes pictures horizontally (slices). Also there is no radiation involved in producing an MRI scan. MRI scans are generally more detailed and the difference between normal and abnormal tissue is often clearer on an MRI scan than on a CT scan.
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How is an MRI scan performed?
An MRI scan can often be carried out as an out-patient procedure, which means that the patient can go home straight after the test. During a scan it is important to lie completely still. Since you're exposed to a powerful magnetic field during the MRI scan, it is important not to wear jewellery or any other metal objects.
| It is also important for a patient to inform staff if they use electrical appliances, such as a hearing-aid or pacemaker, or have any Metal in their bodies such as surgical clips. Orthopaedic materials such as artificial hips or bone screws are not normally a problem.
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Is an MRI scan dangerous?
There are no known dangers or side-effects connected to an MRI scan. The test is not painful, you cannot feel it. Since radiation is not used, the procedure can be repeated without any problems. There can be a small risk to a fetus within the first 12 weeks of pregnancy and therefore MRI scans are not usually performed on pregnant women during this time.
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 | Because patients have to lie inside a large cylinder while the scans are being made, some people can get a little claustrophobic during the test. Patients who are afraid that this might happen should talk to the doctor beforehand, in some cases they may be given medication to help them relax.
The machine also makes a banging noise while it is working, which might be unpleasant. Is important to remember that this is only a loud noise and although unpleasant will not harm you. Patients can ask the technician to provide earplugs if they feel the noise may be a problem. |
