Secondary decline in apparent diffusion coefficient and neurological outcomes after a short period of focal brain ischemia in rats

This study was designed to characterize the initial and secondary changes o f the apparent diffusion coefficient (ADC) of water with high temporal reso lution measurements of ADC values and to correlate ADC changes with functio nal outcomes. Fourteen rats underwent 30 minutes of temporary middle cerebr al artery occlusion (MCAO). Diffusion-, perfusion-, and T2-weighted imaging was performed during MCAO and every 30 minutes for a total of 12 hours aft er reperfusion (n = 6). Neurological outcomes were evaluated during MCAO, e very 30 minutes for a total of 6 hours and at 24 hours after reperfusion (n = 8). The decreased cerebral blood flow during MCAO returned to normal aft er reperfusion and remained unchanged thereafter. The decreased ADC values during occlusion completely recovered at 1 hour after reperfusion, The reno rmalized ADC values started to decrease secondarily at 2.5 hours, accompani ed by a delayed increase in T2 values. The ADC-defined secondary lesion gre w over time and was 52% of the ADC-defined initial lesion at 12 hours. Hist ological evaluation demonstrated neuronal damage in the regions of secondar y ADC decline. Complete resolution of neurological deficits was seen in 1 r at at 1 hour and in 6 rats between 2.5 and 6 hours after reperfusion; no se condary neurological deficits were observed at 24 hours. These data suggest that (1) a secondary ADC reduction occurs as early as 2.5 hours after repe rfusion, evolves in a slow fashion, and is associated with neuronal injury; and (2) renormalization and secondary decline in ADC are not associated wi th neurological recovery and worsening, respectively.