TIM BEDDOW / SCIENCE PHOTO LIBRARY TIM BEDDOW / SCIENCE PHOTO LIBRARY
Positron emission tomography (PET) scan series of the brain of a patient with senile dementia (Alzheimer's disease). The colour-coded scan through different cerebral layers gives brain activity: from low (blue) to high (yellow). PET scanning relies on an injected radioactive tracer to reveal variations in metabolic activity in the brain. Normal brain metabolic activity produces a roughly symmetrical pattern in the yellow areas of left and right cerebral hemispheres. The patchy appearance of this scan indicates degeneration of brain tissue. Symptoms of Alzheimer's disease include memory loss, personality changes, and dis- orientation. There is no known cure.
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