缺血再灌注模型大鼠脑白质扩散张量成像研究

目的:利用MR弥散张量成像(DTI)技术对脑缺血再灌注大鼠的大脑行动态观察,研究其扩散变化规律。方法:将24只成年雄性SD大鼠随机分为假手术组和模型组各12只,假手术组只分离血管,模型组根据线栓法制备缺血2h再灌注模型。术后24h、7d、14d用改良神经功能缺损评分(mNSS)评价大鼠神经功能缺损情况;行T2加权成像(T2WI)、DTI扫描,观察脑梗死体积与相关脑区平均弥散率(MD)和各向异性分数(FA)。结果:模型组较假手术组大鼠缺血再灌注后24h、7d和14d的mNSS评分均升高(均P<0.01),且缺血再灌注后7d的mNSS评分低于上一时间点(P<0.05)。T2WI成像显示,模型组大鼠梗死部位呈异常高信号,随时间推移高信号区域面积减少。DTI结果显示,缺血后24h,模型组较假手术组患侧所有脑区MD值均显著下降(P<0.01,0.05),7d后呈假正常化,14d均高于假手术组(P<0.01,0.05);缺血后24h,患侧胼胝体、海马及纹状体的FA值均显著下降(均P<0.05),7d时均持续下降(P<0.01,0.05),除了胼胝体,其他脑区在14d达到最低水平(P<0.01,0.05)。缺血后24h,除了感觉皮层,健侧脑区MD和FA值均高于假手术组(P<0.01,0.05);缺血后7d,除了胼胝体和海马,其他脑区MD值均低于假手术组(P<0.01,0.05)。结论:DTI能够反映不同时期缺血再灌注后脑白质损伤的变化特点,患侧白质随着时间的推移演变为不可转逆的结构破坏,健侧白质功能变化可能与交互性半球间抑制作用有关。

Diffusion tensor imaging study of white matter in rat cerebral ischemia-reperfusion models

Objective:To observe dynamically the changes of brain diffusion characteristics in cerebral ischemiareperfusion rats by magnetic resonance diffusion tensor imaging(DTI).Methods:Twenty-four male Sprague-Dawley rats were randomly assigned to sham operation group(sham group)and ischemia-reperfusion group(model group),with 12 rats in each group.In the sham operation group,only vessels were separated.The middle cerebral arteries of the rats in model group were occluded for 2 h.At 24th h,7th day and 14th day after surgery,rats were assessed with modified Neurological Severity Scores(mNSS),and scanned with MRI for T2-weighted image(T2WI)and DTI,and the infarct size,mean diffusivity(MD)and fractional anisotropy(FA)were recorded.Results:Compared with the sham group,the scores of mNSS were significantly increased thin the model group at 24th h,7th day and 14th day after surgery(all P<0.01),and the MNSs scores in the model group at 7th day after ischemia-reperfusion were significantly lower than those at the previous time point(P<0.05).T2WI showed that a high signal at the infarct site,and the area of high signal decreased as time passed.In the ischemic side of the brain,the MD values of all brain regions in the model group were significantly lower than those in the sham group at 24th h after ischemia(P<0.01,0.05),and were pseudonormalized at 7th day,higher than those in the sham group at 14th day(P<0.01,0.05);At 24th h after ischemia,the FA values of the corpus callosum,hippocampus and striatum decreased significantly(all P<0.05),and decreased continuously(P<0.01,0.05)at 7th day.The lowest level was found in other brain regions at 14th day,except the corpus callosum(P<0.01,0.05).In the contralateral brain area,at 24th h after ischemia,except for the sensory cortex,the MD and FA values in other brain areas were significantly higher than those in the sham group(P<0.01,0.05);At 7th day after ischemia,except the corpus callosum and hippocampus,the MD values of other brain regions were significdantly lower than those in the sham group(P<0.01,0.05).Conclusion:DTI can reflect the changes of white matter injury after ischemia-reperfusion in different periods.The white matter on the affected side evolves into irreversible structural damage over time,and the white matter on the contralateral hemisphere may be related to reciprocal inter hemispheric inhibition.