Dynamic Evolution Of Focal Cerebral Ischemia Observed By Optical Imaging

Focal cerebral ischemia is one of a common brain blood vessel disease with very high disabled and death ratio. It's very important to study the pathology mechanism and the prevention and cure method of the disease. Optical imaging method can in vivo examine the dynamic process of focal cerebral ischemia at real time. Thereinto, as a brain functional imaging technique in vivo, the optical imaging based on intrinsic signals (OISI) offers the highest spatial resolution and proper temporal resolution thus far obtained. Moreover, laser speckle contrast imaging (LSCI) shows its advantage on measuring the blood flow with high spatiotemporal resolution. It can be used to investigate the focal cerebral cortical blood flow. By studying the dynamic process of focal cerebral ischemia, we can get to know the pathobiology mechanism of the ischemic damage. It's instructive for us to make the diagnosis, therapy and prognosis. In this thesis we apply the OISI to examine the spontaneous spreading depression (SD) waves during the focal cerebral ischemia, the character of optical signals are used to reflect the ischemic penumbra and its dynamic development. We apply the LSCI to investigate the dynamic changes of blood flow during ischemic reperfusion of focal cerebral ischemia and post-ischemia hypoperfusion to study the development rule of cortical ischemic region. The overall review and conclusions of the thesis are listed as following: (1) The optical intrinsic signal imaging (OISI) at 550nm was applied to examine the parietal cortex of focal cerebral ischemia rats with the left middle cerebral artery occlusion (MCAO). A series of spontaneous spreading depression (SD) waves (10.3±4.6 times) were observed during the next 4 hours after MCAO. In the earlier 2 hours, the SD waves usually spread across the whole left parietal cortex, however, the optical signals showed significant regional differences. During the later 2 hours, the waves were restricted in the central parietal cortex, and the propagated area decreased reversely with the increasing times of SD waves. The baseline intensity in the lateral area increased steadily, up to 8.4±1.2% at the end of 4 hours. By TTC staining, the lateral area proved to infract focus. The results suggested the optical imaging supplied an effective method to identify the ischemic penumbra and monitor its dynamic evolution. (2) LSCI was applied to investigate the dynamic changes of blood flow during ischemic reperfusion of focal cerebral ischemia and post-ischemia hypoperfusion. The effect of various ischemic duration on post-ischemic and reperfusion cerebral blood flow has been studied. During 60 min MCAO ischemia, perfusion of cerebral blood flow decreased to 20±3% of baseline while perfusion of cerebral blood flow decreased to 35±3% during 30 min MCAO ischemia. After the occlusion was released , there was a brief period(10～15 min)of post-ischemic hyperemia, perfusion recovered to 80±10% and hypoperfusion maintained at low level of 60～70%. The result showed that hypoperfusion in 60 min group was approximately 10% less than that in 30 min group. And the result demonstrated the status of hypoperfusion is dependent on the duration of cerebral ischemia. The longer is the ischemia, the later is the onset of hypoperfusion and the lower of hypoperfusion. Monitoring the dynamic changes of cerebral blood flow help us to understand and investigate the hemodynamic mechanism of hypoperfusion damage after ischemia.