Imaging local brain function with emission computed tomography.

Positron emission tomography (PET) using 18F-fluorodeoxyglucose (FDG) was used to map local cerebral glucose utilization in the study of local cerebral function. This information differs fundamentally from structural assessment by means of computed tomography (CT). In normal human volunteers, the FDG scan was used to determine the cerebral metabolic response to controlled sensory stimulation and the effects of aging. After stroke, regional brain dysfunction is more extensive than had been suspected on the basis of CT scans. Cerebral metabolic patterns are distinctive among depressed and demented elderly patients. The FDG scan appears normal in the depressed patient, studded with multiple metabolic defects in patients with multiple infarct dementia, and in the patients with Alzheimer disease, metabolism is particularly reduced in the parietal cortex, but only slightly reduced in the caudate and thalamus. The caudate is markedly hypometabolic in Huntington disease, even in the absence of caudate atrophy, and possibly may be mildly hypometabolic even before the appearance of symptoms. The interictal FDG scan effectively detects hypometabolic brain zones that are sites of onset for seizures in patients with partial epilepsy, even though these zones usually appear normal on CT scans. The future prospects of PET are discussed.