大鼠脑缺血再灌注的磁共振扩散加权成像研究

目的：采用磁共振扩散加权成像（DWI）评价大鼠脑缺血早期再灌注的动态变化,观察缺血早期再灌注对脑梗死的保护作用。方法：选取16只SD雄性大鼠,采用线栓法制作右侧大脑中动脉闭塞（MCAO）脑缺血模型,随机分为缺血再灌注组（缺血2h后再灌注）及对照组（永久性缺血）,每组8只。分别于制作MCAO模型后30min、2h、6h、12h及24h行MRI扫描。计算并比较缺血再灌注组与对照组大鼠每次扫描的脑梗死体积、脑梗死体积的增长率、脑梗死最大层面梗死区域的ADC值和rADC值。磁共振检查结束后处死大鼠,断头取脑行HE染色,并与DWI结果进行比较。结果：缺血再灌注组和对照组大鼠MCAO后DWI均显示右侧大脑中动脉供血区异常高信号,ADC图上为低信号。MCAO后2h、6h、12h及24h的DWI图上缺血再灌注组体积增长率均低于对照组,仅12h及24h时差异有统计学意义（P〈0.05）。MCAO后30min缺血再灌注组与对照组梗死区ADC值及rADC值差异均无统计学意义（P〉0.05）,但2h、6h、12h及24h时缺血再灌注组梗死区ADC值及rADC值均明显小于对照组（P〈0.05）。缺血再灌注组与对照组大鼠MCAO后HE染色均显示脑梗死灶体积与相应DWI层面差异无统计学意义（P〉0.05）。结论：DWI是评价超早期脑梗死再灌注的敏感方法,为脑梗死的疗效评价提供客观依据。

Study of reperfusion on MR diffusion-weighted imaging in rat models with cerebral ischemia

Objective：Using MR diffusion-weighted imaging（DWI） to investigate the dynamic changes of cerebral ischemia after early reperfusion in rat models with acute cerebral infarct.Methods：Sixteen male SD rats were chosen,cerebral ischemic models were established by right middle cerebral artery occlusion（MCAO） with floss embolization.The SD rats were randomly divided into reperfusion group（reperfusion 2h following MCAO） and control group（permanent ischemia after MCAO）,with 8 rats in each group.DWI was performed 30min,2h,6h,12h and 24h after MCAO.The infarction volume and the increased rate of infarction of each group displayed on DWI were calculated and compared as well as the apparent diffusion coefficient（ADC） values at the level with the largest infarct area.All the rats were sacrificed after MR scanning protocols were finished and the cerebral ischemic tissues were examined by histopathology with hematoxylin and eosin（HE） staining and compared with DWI findings.Results：All of the two groups showed abnormal hyperintensity in the right cerebral ischemic region on DWI and reduced signal on ADC maps after MCAO.The increased rate of infarcted volume in reperfusion group was lower than that of permanent ischemia group 2h,12h and 24h after MACO respectively,yet it showed statistical differences only at 12h and 24h after MACO（P0.05）.No statistic differences were existed on ADC value and rADC value in the infarcted areas of the reperfusion group and control group at 30min after MCAO（P0.05）,while the ADC values and rADC values in the reperfusion group at 2h,6h,12h,24h were all obviously lower than that of control group（P0.05）.The infarction volumes after MACO on HE staining were in consistent with that on DWI in the two groups with no statistical differences（P0.05）.Conclusion：DWI could sensitively demonstrate early reperfusion after cerebral infarction,it was very helpful in evaluating the therapeutic effect.