Diffusion-Perfusion MR Imaging of Hyperacute Cerebral Infarction Penumbra: An Experiment in Rats

Objective To experimentally study hyperacute cerebral infarction in rats produced by occluding the middle cerebral artery (MCA) with diffusion weighted imaging-perfusion imaging (DWI-PI) technique, to compared imaging findings with pathologic results and to evaluate DWI-PI combination in diagnosing ischemic penumbra in hyperacute cerebral infarction.Materials and Methods Fifty SD rats were randomly and equally divided into five groups. Group A received sham-operation and was used as control group, and DWI-PI scanning was carried out at 30min, 1h, 3h and 6h interval. Groups B, C, D and E received occlusion of the left middle cerebral artery with thread and DWI-PI scanning was carried out at 30min, 1h, 3h and 6h interval, respectively. Apparent diffusion coefficient (ADC), cerebral blood volume or flow (CBV or CBF) and mean transition time (MTT) topographic maps were obtained on a workstation. The relative value (ratio of studied side value to opposite side value) of ADC, CBV, CBF and MTT was calculated. The results were compared with TTC stain and pathologic findings.Results (1) Neither signal intensity alteration on DWI or PI nor pathologic changes were found in the group A rats. (2) In the group B, C, D and E, no difference in perfusion defect extent due to CMA occlusion was seen, which showed high signal on DWI, and ADC ratio was decreased (65.2%) with the D group being the lowest (32.2%) and the E group being almost unchanged (29.9%). On ADC topographic maps the lesion extent increased with the time, and, finally, the extent became basically the same as the abnormal signal area on PI (in the group E). (3) No significant difference in the demonstrated extent of hyperacute cerebral infarction existed between high signal area on DWI and TTC stain area (t test, P0.1). (4) In hyperacute cerebral infarction, DWI-PI unmatched area, the ischemic penumbra, showed no marked pathologic changes, and it was decreased with time.Conclusion In hyperacute cerebral infarction, PI can demonstrate the perfusion defect zone. ADC ratio is decreased, and the lesion's extent is gradually enlarged. High signal area on DWI is in accord with the abnormal staining area on TTC stain. DWI-PI combination can well show the ischemic penumbra and its changing occurred in hyperacute cerebral infarction.