Abstract
Nβacetylaspartate (NAA) is found exclusively in neurons and their processes in the adult brain. Since the regional distribution of NAA may be imaged using magnetic resonance spectroscopic imaging (^1^HβMRSI), a regional measure of neuronal density may be noninvasively obtained. The technique may be particularly useful in the diagnosis of diseases where neurons are selectively injured, since these diseases do not result in definitive changes on conventional imaging studies. The goal of this study was to determine whether ^1^HβMRSI measurement of NAA detects neuronal loss following global ischemia. ^1^HβMRSI was performed in rats 24 h after global ischemia was induced by bilateral carotid occlusion plus hypotension. ^1^HβMRSI showed that NAA was decreased by 29β74% in vulnerable regions, including the cortex, striatum, hippocampus, and, to a lesser extent, the thalamus. No change was observed in the brain stem or cerebellum. Regions where ^1^HβMRSI observed NAA was decreased also had histological evidence of selective neuronal necrosis and showed marked increase of lactate and alanine. These results show that ^1^HβMRSI detected loss of NAA in brain regions with selective neuronal loss, suggesting that ^1^HβMRSI measurements of NAA could detect neuronal loss in a variety of disease states where there is selective neuronal necrosis.