磁共振扩散和灌注加权成像对兔早期脑梗死的诊断价值

Diagnostic value of MR diffusion and perfusion weighted imaging to early cerebral infarction in rabbits

目的:评价扩散加权成像(DWI)和灌注加权成像(PWI)在早期脑梗死诊断中的价值。方法:新西兰大 白兔40只随机分为实验组32只和对照组8只。实验组经眶内入路电凝右侧大脑中动脉,对照组仅暴露同侧大脑 中动脉,不予电凝。2组动物分别在术后0.5h、1h、2h、4h、6h、8h、12h和24h进行MRI检查,扫描序列依次为 SE序列T1WI、T2WI、FLAIR序列、DWI和PWI,比较其检出时间、DWI和PWI异常信号体积变化。取各组不同时点 与DWI检查对应的兔脑组织行电镜检查。结果:实验组大脑中动脉阻塞(MCAO)后0.5hDWI上显示异常高信 号,PWI上显示相对高信号,其范围明显大于DWI异常高信号区,2者不相匹配区为缺血半暗带(IP)。DWI上的异 常高信号区随时间推移,逐渐增大,至24h与PWI上的相对高信号范围吻合。MCAO后4hT2WI和FLAIR序列上 开始显示高信号,但在FLAIR序列上病灶显示更清晰,6h后基底节和顶叶皮层在T1WI上出现低信号,与病理学结 果相符合。对照组MRI检查及电镜检查均未见异常。结论:DWI、PWI可在超急性期显示脑梗死的部位和范围,其 诊断价值优于SE序列T1WI、T2WI和FLAIR序列。DWI与PWI相结合能判断IP的存在与否及其范围。

Aim: To evaluate the value of diffusion weighted imaging (DWI) and perfusion weighted imaging (PWI) in diagnosing early cerebral infarction. Methods: A total of 40 New Zealand rabbits were randomly assigned into experimental group (n=32) and control group (n=8). In experimental group, transorbital electrocoagulation was carried out to occlude the right middle cerebral artery. For control group, operation was performed only to expose the right middle cerebral artery, and not to occlude it. Both groups were examined with MR scanner at 0.5 h, 1 h, 2 h, 4 h, 6 h, 8 h, 12 h,and 24 h after operation, respectively. The scanning sequences were arranged as SE T_1WI, T_2WI, FLAIR sequence, DWI as well as PWI. Specimens of brain tissue which was obtained for DWI scan at each time point were observed under electron microscope. The finding time of cerebral infarction was compared.The volume change of abnormal signal intensity on DWI and PWI was analyzed.Results: In experimental group, the infarction area showed abnormal high signal intensity on DWI and relatively high signal intensity on PWI 0.5 h after middle cerebral artery occlusion(MCAO), whereas the area of the relatively high signal intensity on PWI were larger than that on DWI, and the mismatched region was indicated as ischemic penumbra (IP). The area of abnormal signal on DWI enlarged with time and matched the relative high signal region on PWI by 24 h after MCAO. Abnormal high signal initially occurred in the basal ganglia and cortical areas on both T_2WI and FLAIR sequence 4 h after MCAO, and low signal in that area could be found on T_1WI 6 h after MCAO. Abnormal signals were demonstrated more clearly on FLAIR sequence than on SE sequence. No abnormality was found in control group. Conclusion: DWI and PWI can detect the position and extent of the cerebral ischemia at the superacute stage, and are superior to SE T_1WI, T_2WI and FLAIR sequence in diagnosing superacute cerebral infarction. DWI combined with PWI can detect IP and its extent.