| [Objective] Cerebral ischemic stroke was a disease of hLgh incidence, high mortality and high deformity, which was a hotspot in clini玞al and basic studies. The evolvement of ischemic stroke could be monitored Tby serial MR scans. High signal intensity on T1WI was found in subacute infar-ction or after transient ischemic attacks, but the neurological symptom did not deteriorate. Our study was to realize the specific signal after cerebral ischemia by establishing the rat model of middle cerebral artery occlusion (MCAO) and prrovide useful information for clinical treatment.[Materials and Metheds] A total of 56 adult male Wistar rats weighing 250 g~300 g were used in this study. They were divided into two groups randomly, experimental group (Tl group, n=49) and contrast group (TO group. n=7). The rat model of MCAO was performed according to the intraluminal filament technique modified by Zea-Longa. In contrast group, the occluding filament was inserted only 15mm above the carotid bifurcation. Reperfusion was accomplished by gently withdrawing the occluding filament about 10mm according to different ischemic time. Tl group was divided into 4 subgroups furth ermore: Tl-a subgroup (n=13), 15 minute's MCAO; Tl-b subgroup (n=12). 30 mLnute's MCAO: Tl-c subgroup (n=12), 60 minute's MCAO; Tl-d subgroup (n=112). permanent MCAO. SPIO (superparamagnetic iron oxide) perfused T2WI was used toestimate whether the operation of rat model was succeed.MR studies were performed on a 1.5T unit using a temporomandibular coil. T2 weighted fast spin-echo(FSE)images and pre-and post-contrast Tl weighted SE (spin-echo) MR images were obtained. 3, 5, 7, or 14 days after operation, each group was examined by serial MR scans to observe whether the short Tl signal appeared. After the last MRI examination they were executed respectively to observe the corresponding pathological change . The images were evaluated by two experienced radiologist to observe the position and the time that the short Tl signal appeared. The signal intensities of ischemic side(SL) and contralateral tissue(ST) on T1WI were measured using a 1mm2 ROI(region of interest) respectively. Contrast ratios(CR) of lesion to normal contralateral tissue was determined as follows: CR= ( SL-ST) /ST. Related statistical analysis was performed.[Results] In TO group, no short Tl signal was observed in bilateral cerebral hemispheres, and the corresponding pathological examination was normal. In Tl-a subgroup, short Tl signal was observed at the 14th day , H&E staining showed laminar cortical necrosis, microhemorrhage and fat-laden vacuoles. Slight breakage of the blood brain barrier (BBB) was found in electronic examination. In Tl-b, Tl-c and Tl-d subgroups, high signal intensity on Tl weighted imaging appeared at the 3th day's MRI examination. It mainly located in cortical region of the ischemic side. Histological changes was whole cortical necrosis, regional hemorrhage, glial proliferation and fat-laden vacuoles. In electronic examination, injury of the BBB was present, floccule outside the cell increased, neurons was destroyed or appeared ischemic change, cellular fragment was formed, the axis was injuried, and the glial cells proliferated.The value of Tl signal intensities obtained was analyzed with statistical methods. The signal intensity of the lesion on T1WI was higher than that of the contralateral side (.PO.05). The intensity of short Tl signal at different ischemic time was different. It was most prominent at the 5th day. which had a lower trend at the 7th day. The appearance of short Tl signal was markedly related to the time of ischemia-reperfusion (.PO.05). The time of short Tl signal appeared likely hadassociated with the different ischemic time (P = 0.05).(Conclusion] In the study of local cerebral ischemia, the appliance of SPIO perfused T2WI may become the standard to verify the success of animal model. The pathological result suggested that short Tl signal after cerebral ischemia was induced by hemorrhage, fat-laden vacuoles, and myelino...
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