Medical Questions » Radiology Questions » Question No. 842
| Question: | What is involved in an MRI scan? I have seen numerous doctors about my headaches and fainting, and now a neurologist wants me to have one of these tests. |
| Answer: | Magnetic resonance imaging (MRI), or nuclear magnetic resonance (NMR) as it is sometimes called, is a new technique of scanning the body. It is based on the fact that living tissues give off their own special electromagnetic signals, depending largely on their water content, and if the tissues are exposed to a magnetic field the signals can be picked up and read. Hence, a very strong magnetic field is created by special magnets, and different areas of the body absorb different amounts of magnetism according to their water content. A magnetic absorption photograph is then built up, and can be seen and analysed, slice by slice, on a computer screen in much the same way as a CT scan. MRI is particularly useful as it ignores bones (which contain little water) and shows up soft tissue, which is the opposite of X-rays.
MRI is especially helpful in diagnosing diseases in the brain and spinal cord. The picture obtained by MRI of the brain clearly shows the difference between the white matter (nerve fibres) and the grey matter (nerve cells). Tumours that are not appatent on a CT scan ate sometimes revealed by MRI, not only in the brain but in organs deep within the abdomen such as the liver.
MRI is completely safe. Its main disadvantage is that the equipment is enormously expensive (approximately twice as expensive as a CT scanner) and must be housed in a special magnetically sealed room. As a result, high fees must be charged for its use, and not all of these arc covered by Medicare or private health insurance.
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