Heterogeneity evaluation of multi-high b-value apparent diffusion coefficient on cerebral ischemia in MCAO rat

PURPOSE: To assess brain damage in a rat model of cerebral ischemia based on apparent diffusion coefficient (ADC) data obtained from multi-high b-values and evaluate the relationship between Aquaporin 4 (AQP4) expression and ADC. METHODS: Thirty eight male Sprague–Dawley rats were randomized into two groups: (1) sham controls (n = 6) and (2) cerebral ischemia (successful model, n = 19). All rats underwent diffusion-weighted imaging (DWI) with both standard b-values and multi-high b-values (2,500–4,500 s/mm(2)) using a 3.0-T device. Standard ADC (ADC(st)) maps and multi-high b-value ADCs (ADC(mh)) were calculated, respectively. Aquaporin 4 expression was quantified using Western blot. Relative values of ADC(st) and ADC(mh), AQP4 expression were compared between the sham group and the ischemia group. Correlations between ADC values and AQP4 expression were evaluated. RESULTS: At 0.5 h after suture insertion, the value of ADC(mh) on the lesion was obviously decreased, and there was no difference in lesion volume when compared with ADC(st). After reperfusion, besides similar regions where ADC(st) values decreased, we also found additional large values on ADC(mh) within the cortex of the ipsilateral side or surrounding the lesion. The lesion evolution of the large value on ADC(mh) was quite different from other indicators. But the total ADC(mh) values were still significantly associated with ADC(st). The AQP4 protein expression level was appreciably increased after middle cerebral artery occlusion (MCAO), but there was no correlation between AQP4 expression either with ADC(mh) or ADC(st). CONCLUSION: We found the large values on ADC(mh) during the progression of cerebral infarction is varied, but there was no correlation between ADC(mh) values and AQP4 expression. ADC(mh) may indicate the heterogeneity of ischemia lesions, but the underlying pathological basis should be further explored.