Diffusion Weighted Imaging In Acute Brain Ischemia Of Rats With Monoexponential And Biexponential Models

Purpose:To evaluate the value of diffusion weighted imaging in acute ischemia by observing the changes in MR parameters derived from monoexponential and biexponential analysis in middle cerebral artery occlusion (permanent ischemia and reperfusion) model during24h of ischemia.Materials and Methods:Eight mature male wistar rats were taken in control group and22in MCAO group, the MCAO group was divided into permanent ischemia group (11) and reperfusion after1.5h (11) group. The sequences included coronal T2WI, T1WI, tradition DWI (b=1000s/mm2) and multi-b value DWI (b=0、20、50、100、200、400、600、800、1000、1200、1600、2000、2400、2800、3200、3600、4000s/mm2), which were performed before and l0min,30min,1h,3h,6h,12h and24h after MCAO. ADC maps were created using b-values of0and1000s/mm2, ADCsiow, ADCfast and Afast were created by applying the biexponential model using the b-values above1000s/mm2. The rats were decapitated after24h of MRI examination. TTC stain was used to determine the infarction size. EB stain was performed in4rats with permanent ischemia and after reperfusion, after3h and6h of MCAO to determine whether the BBB was broken down at that time.Results:(1) In permanent ischemia group, the volume of hyperintensity in DWI gradually increased and reached its maximum at24h. In reperfusion group, the volume of hyperintensity in DWI was reduced after1.5h reperfusion, then gradually increased and reached its maximum at24h and the volumes were similar to that before reperfusion, but smaller than the permanent ischemia group at24h.(2) In permanent group, ADC, ADCslow and Afast deceased at first and reached to the minimum value at6h, then they increased slightly. ADCfast deceased after the ischemia and maintained at a low level. In reperfusion group, the ADC, ADCslow, Afast and ADCfast deceased after the occlusion and significantly increased after1.5h of the reperfusion, then they decreased gradually to the lowest level at24h. These values were similar to that in the permanent group at24h.(3) Beside24h, there were significant differences in ADC, ADCsiow and Afast between permanent ischemia group the reperfusion group. There was a significant difference in Afast only at3h between the two groups.(4) EB extravasations were observed in the ischemia lesion of the brain tissue in both permanent group and reperfusion group at3h and6h.Conclusion:The ischemic penumbra (IP) existed in acute ischemia stroke, which could be partially saved after timely reperusion. The BBB opened at3h after the occlusion both in permanent ischemia group and reperfusion group. The parameters of ADCslow, ADCfast and Afast created by the biexponential model had the ability to distinguish the difference of the restriction of water between intra and extracellular space in the process of the ischemia and reflect the movement direction of water molecules.