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In this issue of The Journal of Nuclear Medicine, Tsuchida et al. (1) report 2 interesting relationships that they observed between proton magnetic resonance spectroscopy (MRS) measurements and measurements of hemodynamics and oxygen metabolism with PET in 11 patients with severe occlusive carotid artery disease. First, they report that the ipsilateral-contralateral ratios of N-acetyl-aspartate to the sum of creatine and phosphocreatine (NAA/ Cr) measured in hemispheric white matter correlated significantly with ipsilateral-contralateral cortical blood flow and with cortical oxygen metabolism. Because NAA is generally assumed to be restricted to neurons, this finding can be interpreted as indicating neuronal loss in the white matter distal to carotid artery occlusive disease that parallels the reduction in cortical blood flow and metabolism in the same hemisphere. Such an interpretation is consistent with previous pathologic findings of selective neuronal necrosis in both human and animal brains subjected to focal ischemia (2). Findings of incomplete brain infarction have also been reported on the basis of reduced uptake of the central benzodiazepine radioligand [^sup 123^I]iomazenil (3) in noninfarcted areas of brain or failure of cerebral oxygen metabolism to improve in noninfarcted brain after extracranial-intracranial bypass surgery (4). Second, Tsuchida et al. report that the ipsilateral-contralateral ratio...