急性脑静脉闭塞磁共振扩散张量成像的实验研究

Experimental Study on MR Diffusion Tensor Imaging in Acute Cerebral Venous Occlusion

目的对急性脑静脉闭塞模型进行磁共振扩散张量成像(DTI),观察脑实质损害的扩散规律及脑白质纤维束的完整性。材料与方法取家猫30只随机分为手术组(n=24)和假手术组(n=6)。手术组制备急性脑静脉闭塞动物模型,假手术组仅行开颅上矢状窦暴露。术后采用常规MRI和DTI对各组模型脑实质损害病灶进行连续动态观察,测量病变区的平均扩散系数(ADCav)和各向异性分数(FA)值,计算病变区与健侧区的ADCav、FA比值,用纤维示踪技术(FT)显示脑白质纤维束的完整性,并与病理学对照。结果手术组24只猫,9只常规MRI检查为阴性;15只猫脑实质出现异常信号,术后1 h ADCav值较健侧降低,3 h后ADCav值较健侧逐渐增高,12 h后增高明显。FA值于术后各时间点均降低。各时间点病变区与健侧ADCav、FA值差异有统计学意义(P<0.05)。各时间点ADCav、FA比值差异有统计学意义(F值分别为62.07、9.37,P<0.05)。术后1 h,FT显示脑白质纤维束移位和穿过病灶区,6 h后脑白质纤维束断裂、破坏,12 h后脑白质纤维束于病灶边缘处中断。术后1 h病灶区出现细胞毒性脑水肿,3 h后以血管源性水肿为主,12 h后出现静脉性脑梗死、脑出血。假手术组未见上述异常表现。结论DTI能清楚显示并定量判断急性脑静脉闭塞脑实质损害的动态变化规律,FT能更好地显示脑白质纤维束的受损和移位。

Objective To evaluate a model of acute cerebral venous occlusion with MR diffusion tensor imaging （DTI） , and to observe diffusion regularity of the brain parenchymal lesions caused by the occlusion and the integrity of white matter fiber tracts. Materials and Methods Thirty cats were randomly divided into 2 groups, operation group （ n = 24） and sham operation group （n = 6 ）. Craniotomy was performed and the cellulose acetate polymer （CAP） solution was injected into the superior sagittal sinus （ SSS ） to prepare a model of acute cerebral venous occlusion in operation group. Craniotomy was performed only to exposure SSS in sham operation group. Conventional MRI and DTI were continually performed at an interval of 1, 3, 6, 12, 24 and 48h after operation for each group to observe the brain parenchymal lesions. Parametric maps were reconstructed, average diffusion coefficient （ADCav） and fractional anisotropy （FA） were measured in the lesions and the ratios to the contralateral corresponding regions were calculated. The integrity and continuity of white matter tracts were showed by fiber tractography （FT）. MR data was compared with pathologic examination. Results In operation group, the brain parenehymal lesions were detected in 15 cats. Compared with contralateral corresponding regions, ADCav values decreased in 1h, increased in 3h and increased obviously in 12h. FA values were decreased at each time point after operation. ADCav and FA values of the lesions showed significant difference （ P 〈 0.05 ）. The ADCav ratio and FA ratio showed significant difference （ F = 62.07 and 9.37 respectively, P 〈 0.05 ）. FT maps showed displacement of white matter fiber tracts and running through the lesions in lh, damage or disruption in 6h and breaking in the edge of the lesions in 12h after occlusion. Pathologic examination： showed cytotoxic edema of the lesions in 1 h, mainly vasogenic edema in 3h, followed by venous hemorrhage and infarction in 12h after occlusion. No abnormal change was observed in sham operation group. Conclusion DTI can clearly depict and assess quantitatively the dynamic changes of brain parenchymal lesions in acute cerebral venous occlusion, FT is better in displaying damage or displacement of white matter fiber tracts than conventional MRI.