Laser Speckle Contrast Imaging And Its Biomedical Applications

Monitoring of microcirculation blood flow is an important medical diagnose and surgical tool, which can reflect the functional activities and decease pathology of biotissue. Laser speckle contrast imaging (LSCI) provides full-field and real-time investigation of microcirculation blood flow in vivo with high spatiotemporal resolution, including several advantages, such as non-contact, noninvasive and high speed imaging. Therefore, LSCI is a well suited for the measurements of capillary diameter, capillary density, blood flow velocity and blood perfusion. The potential application could be involved in inflammation, hemorrhage, oedema, irritability, shock, cancer, burn assessment, frostbite and radiation damage. The feasibility of mapping flow or perfusion with LSCI would be a powerful in disease diagnoses, pathography analysis and therapy. In this thesis we present basic principle and the system of LSCI, which are applied in real-time investigation of photodynamic therapy (PDT) induced vascular damage and real-time investigation of capillary flow and diameter changes during ischemic reperfusion of focal cerebral ischemia and post-ischemia hypoperfusion. The overall review and conclusions of the thesis are listed as following: 1) The compositions and performance of LSCI system has been studied. Theory and model experiments were carried out to obtain the relationship between contrast of time-varying speckle, correlation time and exposure time. It is found that the best exposure time for time-varying speckle measurement is larger than 20 ms. Additionally, maximum imaging depth of the system is 1 mm and optimum velocity with best contrast dynamic range is less than 2 mm/s. For spatial statistic analysis of speckle contrast images, a square of 7×7 pixels is an optimized compromise when the speckle size is approximately 1.5 pix/sp. The effect of tissue optical parameter on the measurement has been discussed, showing the independence of speckle contrast on blood oxygen concentration. In term of analysis of laser speckle images, a method is explored to extend the dynamic range of speckle contrast; the spatial statistic and temporal statistic method of speckle images were described and compared in terms of temporal resolution, spatial resolution and complexity of algorithm. Moreover, the application of temporal cluster analysis on speckle images was presented. 2) LSCI has been applied in real-time investigation of photodynamic therapy (PDT) induced vascular damage by use of the model of chick chorioallantoic membrane (CAM). The advantages of CAM model in optical imaging were presented. The experiments were carried out in different light irradiation dose group and different photosensitizer does group. The results demonstrate that the size of vessel shows more change specificity than its type (arteriole or venule). When using blood perfusion instead of vascular diameter as the quantitative assessment, the functional vascular changes and morphological vascular changes can be considered simultaneously. So the damage impact of PDT on the blood vessel can be assessed by monitoring the hemodynamics of peripheral vascular of tumor to confirm the photosensitizer dose and laser light dose of PDT, that can be used to propose the optimized tumor treatment. 3) LSCI was applied in real-time monitor of capillary flow and diameter changes during ischemic perfusion and post-ischemia hypoperfusion. The effect of various ischemic duration on post-ischemic and reperfusion cerebral blood flow has been studied. It is shown that focal cerebral ischemia was induced by using the middle cerebral artery occlusion (MCAO) model, for 30 or 60 min, followed by reperfusion up to 120 min. During 30 min MCAO ischemia, perfusion of cerebral blood flow decreased to 35 ±3% of the baseline. After 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. The vascular diameter decreased to 80 ±3% of the baseline during 60 min ischemia and 90 ±3% during 30 min ischemia, while the vascular diameter was 90% of the baseline during hypoperfusion. The result demonstrated that 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 changes of cerebral blood flow and vascular diameter in ischemic area during ischemia and reperfusion,can not only help treatment of drugs and prevent ischemic stroke, but also help understand and investigate the hemodynamic mechanism of hypoperfusion damage after ischemia.