TIM BEDDOW / SCIENCE PHOTO LIBRARY TIM BEDDOW / SCIENCE PHOTO LIBRARY
Positron emission tomography (PET) scan of the brain (basal ganglia level) of a normal human subject. The colour-coded scan through this cerebral layer shows brain activity: from low (blue) to high (yellow). PET scanning relies on a radioactive tracer, injected into the bloodstream, to reveal metabolic activity in the brain. As seen here, normal brain metabolic activity produces a roughly symmetrical pattern in the yellow areas of left and right cerebral hemispheres. In many brain dysfunctions (such as Alzheimer's disease, epilepsy and schizophrenia), PET scans are useful in pinpointing specific brain areas which are metabolically affected by disease.
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