Click: MRI stands for magnetic resonance imaging.  Rather like a CAT scan it can take a picture of
a  thin slice of brain - think of a meat slicer in a delicatessen - followed by a picture of the next slice, and the next.

The stack of pictures are combined in a computer to create an accurate  model -
a blueprint of the brain - that can be used to locate abnormalities and plan an operation.

Unlike the meat slicer, they are non-invasive technologies: CAT scans use radiation, MRI's use radio waves and measure the response from each individual atom [explain briefly how it works in later section]. MRI's are particularly useful for areas of soft tissue, such as the liver, the kidneys and... the brain. They can even distuinguish between areas of diseased and healthy tissue, such as a tumour growing on a gland.

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