大鼠急性脑梗死后不同区域扩散和灌注成像的变化特点

Characteristics of diffusion and perfusion-weighted MRI in different cranial infarction areas of acute stroke in a rat model

目的探讨急性脑缺血后不同区域的PWI和DWI随时间变化的规律及其病理基础,确立评估急性脑缺血可逆性梗死的MRI特异指标及标准。方法利用线栓法建立实验大鼠急性脑缺血模型。应用随机数字表法进行随机分组,A组(单纯脑缺血组):①1.5h(3只),②3h(6只),③6h(3只),④9h(5只)。另设立假手术组作对照组(B组,5只,仅分离颈总动脉)。对上述各组大鼠在规定的时间内行MRI检查,重点测量梗死中心区、梗死边缘和皮质区的表观扩散系数(ADC)、相对血流量(rNEI)、相对峰值时间(rTTM)、信号强度时间曲线的相对上升斜率(rMSI)和信号强度时间曲线的相对下降斜率(rMSD)。将结果与TTC染色、光镜、电镜、免疫组化和激光扫描共聚焦显微镜(LSCM)的结果进行对照。结果A组于缺血1.5h后梗死中心区ADC降低(0.29×10-3mm2s),不同时间组间差异无显著性(P>0.05)。梗死边缘区ADC随时间延长进一步降低,其ADC于脑缺血后1.5h与9h、3h与9h之间存在显著差异(P<0.05)。脑缺血后1.5h,梗死中心区、皮质区之间ADC差异显著(P<0.05),ADC位于皮质区与梗死边缘之间差异无显著性(P>0.05)。对照病理结果和LSCM结果,ADC大于0.51×10-3mm2s,rNEI大于70%和rTTM小于120%,提示脑组织的损伤轻微或可逆。结论急性脑缺血后其DWI、PWI参数值随时间、空间变化,DWI、PWI的半定量化分析,可以鉴别脑缺血发生后脑缺血不同区域的变化,为我们鉴别缺血半影区的存在及范围提供新的方法。

Objective To investigate the Characterization of DWI and PWI during cranio-ischemia in assessment of reversible ischemic penumbra in rats. Methods All 22 rats were randomly divided into 2 groups, group A （ n = 17） . The left middle cerebral arteries were occluded with filaments for 1.5 hours （ n = 3） , 3 hours （ n = 6）, 6 hours （ n = 3） , 9 hours （ n = 5） respectively： group B （ n = 5） with sham operation was set up for control study. The DWI and PWI were performed when rats experienced neurologic deficits. Their apparent diffusion coinfficient （ADC）, relative negative enhancement integral （rNEI）, relative time to minimum （rTFM）, relative max slope of increase （rMSI） , relative max slope of decrease （rMSD） were measured at areas of ischemic core, ischemic margin, and cortex. Two rats of each sub-group were performed with TTC staining, histopathology, immunocheministry and laser scanning confocal microscope （ISCM） for control study. Results ADC values significantly decreased in the ischemic core （0.29 × 10^-3mm^2/s） compared with ischemic margin （0.51 × 10^-3mm^2/s）） and cortex （0.59 × 10^-3mm^2/s） （P 〈 0.05） at 1.5 hours. Over 3 hours, the ADC values in the ischemic margin continued to decrease according to the former time sets gradually, with significantly difference （ P 〈 0.05）. Of all perfusion parameters, the rNEI and rTTM were more sensitive than rMSI and rMSD in detecting perfusion deficit. In short, ie, 0.51 ×10^-3 mm^2/s for ADC, 70% for rNEI and 120% for rTFM would be the optimal standard suggesting the mild cranial tissue damage or with reversible tissue damage. Conclusions Semi-quantitative parameters based on DWI and PWI of acute cranial ischemia can provide us new modalities for distinguishing and confirming the existanees and extent of ischemic area.