Functional Brain Imaging

If your structural imaging is normal but your doctor suspects that you might have Alzheimer's disease or another type of degenerative condition, he or she might also recommend a single photon emission computed tomography (SPECT) scan or a positron emission tomography (PET) scan. Rather than producing a picture of brain structure, these imaging techniques look at how the brain is functioning. SPECT traces perfusion (blood flow), and PET maps glucose metabolism. Decreased perfusion or energy metabolism in the temporal and parietal regions of the brain is the functional "signature" of Alzheimer's disease. Other brain disorders produce distinctive functional imaging patterns. These scans can reveal abnormalities even when an MRI appears normal.

Functional MRI (fMRI) is a newer imaging methodology that is being used extensively in research to determine which brain regions are activated during different types of cognitive processing. It uses conventional MRI technology, but it acquires a series of images so rapidly that they can be analyzed to reveal subtle changes in blood flow during performance of a specific cognitive task. In all likelihood, fMRI will soon gain acceptance as another useful diagnostic clinical tool.

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