脑梗死前期脑局部微循环障碍CT灌注成像的实验研究

CT perfusion imaging on the disturbance of regional cerebral microcirculation in a pre-infarction period : an experimental study

目的 从微循环的角度探讨脑梗死前期CT灌注成像表现及其病理基础 ,以及星形细胞与脑局部微循环的关系。方法 建立大鼠脑局部低灌注模型和脑局部星形细胞水肿模型 ,在动态CT脑灌注成像检查后处死 ,分别作灌注CT参数图、红四氮唑 (TTC)染色、电子显微镜 (简称电镜 )和光学显微镜 (简称光镜 )观察。脑局部低灌注模型作了局部脑血流量 (regionalcerebralbloodflow ,rCBF)、局部脑血容量 (regionalcerebralbloodvolume ,rCBV)、平均通过时间 (meantransittime ,MTT)和最大峰值时间 (time to peak ,TTP)比值 (病侧 健侧 )测量。结果 大鼠脑局部低灌注模型实验组的rCBF和MTT参数图显示病变侧低灌注区 ,rCBV和TTP参数图未见异常。rCBF、rCBV、MTT和TTP的比值范围分别为 :0 3 9～ 0 55、0 92～ 1 0 0、1 2 0～ 1 50和 1 0 0～ 1 0 0。电镜见星形细胞水肿 ,肿胀的星形细胞足板挤压毛细血管使管腔狭窄或闭塞 ;神经元表现正常或有轻度可逆损伤。假手术组各个参数图、TTC染色、电镜以及光镜未见异常。大鼠脑局部星形细胞水肿模型实验组 4只大鼠的rCBF和MTT参数图均见星形细胞水肿所造成的局部低灌注带和局部MTT延长区域 ,其中 3只rCBV参数图显示异常低灌注区 ,2只TTP参数图显示TTP异常延长区域。rCBF、rCBV。

Objective To investigate the CT perfusion imaging and the pathological features on the disturbance of regional cerebral microcirculation in a pre-infarction period, and to evaluate the relationship between the astrocytes and regional cerebral microcirculation. Methods Dynamic CT perfusion imaging of the models with regional cerebral hypoperfusion and astrocytic swelling in rats was performed to assess the presence or absence of the disturbance of regional cerebral microcirculation. Then, the histopathologic examination was made for both models, respectively. The ratios of side-to-side were measured at hypoperfusion areas in the models of regional cerebral ischemia. Results Regional hypoperfusion was revealed by regional cerebral blood flow (rCBF) and mean transit time (MTT) maps in the group of hypoperfusion for 6 hours. Regional cerebral blood volume (rCBV) and time-to-peak (TTP) maps were normal in that group. The ratios of rCBF, rCBV, MTT and TTP were 0 39-0 55, 0 92-1 00, 1 20-1 50 and 1 00-1 00 respectively. Astrocytic swelling pressing the capillary wall was obvious and subtle neuronal reversible degeneration was occasionally found. TTC stain was normal. In the tACPD group of astrocytic swelling, the abnormal hemodynamic regions on rCBF and MTT maps were found. The rCBV maps of 3 rats in the tACPD group showed the area of reduced rCBV. In 2 rats of tACPD group, the areas of delayed TTP were also found. The ratios of rCBF, rCBV, MTT and TTP were 0 25-0 44, 0 70-1 01, 1 20-2 00 and 1 02-1 45 respectively. TTC stain was negative. Electron microscope study revealed remarkable swelling of astrocytes, especially endfoot processes of astrocytes around capillaries. The abnormal hemodynamic region on rCBF and MTT maps matched with abnormal extent on histopathologic examination. The rCBV and TTP maps appeared normal. Conclusion The astrocytes can react in a way faster than the neurons in the pre-infarction period, viz. astrocytic swelling. The swelling of astrocytic foot, which pressed capillary vessel, induced the disturbance of regional cerebral microcirculation, and then aggravated hypoxic ischemic state in regional brain parenchyma. Perfusion CT and its parameters' analysis may play an increasing role to delineate the reversible hypoperfusion areas in pre-infarction period. Analyzing the relationship of rCBF and rCBV is very helpful to know the status of the capillary vessels in regional cerebral hypoperfusion area.