超急性期脑缺血静息态脑功能磁共振网络信号变化的实验研究

Functional connectivity analysis of superacute cerebral ischemia in rats： a resting-state functional MRI empirical study

目的 应用低频血氧水平依赖振荡（LFBF）信号和功能连接分析方法探讨大鼠脑缺血超急性期静息态脑功能磁共振信号的变化.方法 选择SD大鼠28只,吸入麻醉后以线栓法制作大鼠大脑中动脉栓塞模型（MCAO）,模型制作前及制作成功后1、2 h分别置入7.0 T的小动物磁共振仪进行磁共振成像扫描,采集鼠脑解剖及功能成像数据;分别以缺血侧皮质和对侧脑相应部位为感兴趣区,计算感兴趣区内的LFBF信号平均强度;同时以功能连接分析方法对各兴趣区之间、兴趣区和全脑之间的脑功能数据进行功能相关性分析.结果 （1）缺血后缺血区皮质LFBF信号强度低于对侧皮质信号强度,也低于造模前的皮质信号强度;（2）缺血区皮质与种子区之间的功能相关性减低,2 h后边缘有所恢复;而对侧正常皮质与种子区之间的功能相关性增高,以2 h时为明显;缺血皮质和对侧皮质之间的平均相关系数差异有统计学意义（P＜0.05）.结论 应用LFBF信号变化及功能连接分析法研究缺血早期状态的脑功能可能对局限性脑缺血早期诊断、判断脑神经活动生理变化及评估脑缺血预后提供了一种新的方法.

Objective To investigate the change of low-frequency blood-oxygenation-leveldependent fluctuation （LFBF） after cerebral ischemia by functional connectivity analysis in the resting state.Methods Superacute stroke rat-models with middle cerebral artery occlusion （MCAO） were employed in this study. Spontaneous fluctuations were recorded using a series of gradient-recalled echo-planar imaging （EPI） images before creation of the MCAO, and the same scan protocols were duplicated at the time of 60min, 2 h after creation of the MCAO. FMRI signal time series from the different ROIs of ischemic cortex and normal cortex were preprocessed and low pass filtered. After preprocessing, the serial fMRI data was obtained by fast Fourier transformation to calculate the amplitude of the low-frequency fluctuations.Meanwhile, time course signal changes from a seed voxel of normal cortex were correlated with every voxel in the brain. Statistical analysis was performed across all rats to determine the extent of spatial correlation between regions. Results The amplitude of LFBF in the ischemic cortex between 0. 01 and 0. 1 Hz was lightly decreased during the superacute ischemic stroke. Howerever, the amplitude of LFBF in contralateral cortex was increased after 2 hours. Spatial distribution of LFBF, from cross-correlation analysis, indicates that the substantial inter-hemispheric synchrony of ischemic region was decreased and of contralateral cortex was enhanced during the superacute ischemic stroke. Conclusion The contrast behavior of the resting state BOLD signal fluctuations and a intra-hemispheric symmetry in the LFBF with similar phase characteristics in most other regions during superacute ischmic stroke can be implied a new approach to detect the physiological activity functions and the distinct resting neural networks after the acute ischemic stroke takes place.