Changes in metabolites and tissue water status after focal ischemia in cat brain assessed with localized proton MR spectroscopy

Localized proton spectroscopy was used to monitor changes in metabolism and the biophysical status of tissue water in cat brain induced by occlusion of the middle cerebral artery. Changes in the intensity of N‐acetyl‐aspartate (NAA), total creatine (tCr), and lactate (Lac) signals in localized volumes of interest in the ischemic hemisphere were quantified relative to the preischemic signal. Changes in the apparent diffusion coefficient (ADC), T₁‐ and T₂‐relaxation times of water in those volumes were also quantified. Lactate was shown to increase rapidly in the first 0.5−2.0 h of ischemia and stabilized afterwards. The ADC of water started to decrease from 0.64 × 10⁻⁹ m2/s to 0.54 × 10⁻⁹ m2/s in the first minutes following occlusion, as was shown in two cases where ADC was measured with high temporal resolution, and stabilized after approximately 3 h at 0.38 × 10⁻⁹ m2/s (n = 6). NAA and tCr decreased by 35% (P< 0.0001) and 30% (P< 0.005), respectively, in the first 8 h of ischemia in comparison with the preischemic control levels. T₁ and T₂ gradually increased with 0.3 s (P< 0.0001) and 5.2 ms (P< 0.0001), respectively, during the same time span.