Correcting the detrimental effects of nonuniform intensity distribution on fiber-transmitting laser speckle imaging of blood flow.

Laser speckle spatial contrast analysis (LSSCA) is superior to laser speckle temporal contrast analysis (LSTCA) in monitoring the fast change in blood flow due to its advantage of high temporal resolution. However, the application of LSSCA which is based on spatial statistics may be limited when there is nonuniform intensity distribution such as fiber-transmitting laser speckle imaging. In this study, we present a normalized laser speckle spatial contrast analysis (nLSSCA) to correct the detrimental effects of nonuniform intensity distribution on the spatial statistics. Through numerical simulation and phantom experiments, it is found that just ten frames of dynamic laser speckle images are sufficient for nLSSCA to achieve effective correction. Furthermore, nLSSCA has higher temporal resolution than LSTCA to respond the change in velocity. LSSCA, LSTCA and nLSSCA are all applied in the fiber-transmitting laser speckle imaging system to analyze the change of cortical blood flow (CBF) during cortical spreading depression (CSD) in rat cortex respectively, and the results suggest that nLSSCA can examine the change of CBF more accurately. For these advantages, nLSSCA could be a potential tool for fiber-transmitting/endoscopic laser speckle imaging.

Simultaneous automatic arteries-veins separation and cerebral blood flow imaging with single-wavelength laser speckle imaging.

Automatic separation of arteries and veins in optical cerebral cortex images is important in clinical practice and preclinical study. In this paper, a simple but effective automatic artery-vein separation method which utilizes single-wavelength coherent illumination is presented. This method is based on the relative temporal minimum reflectance analysis of laser speckle images. The validation is demonstrated with both theoretic simulations and experimental results applied to the rat cortex. Moreover, this method can be combined with laser speckle contrast analysis so that the artery-vein separation and blood flow imaging can be simultaneously obtained using the same raw laser speckle images data to enable more accurate analysis of changes of cerebral blood flow within different tissue compartments during functional activation, disease dynamic, and neurosurgery, which may broaden the applications of laser speckle imaging in biology and medicine.

Investigating the effects of dimethylsulfoxide on hemodynamics during cortical spreading depression by combining laser speckle imaging with optical intrinsic signal imaging.

BACKGROUND AND OBJECTIVES: Cortical spreading depression (CSD) is an important pathological model to study cerebral ischemia and migraine. In pharmacological studies of CSD, dimethylsulfoxide (DMSO) is an efficient solvent for water-insoluble drugs. Previous studies indicated that DMSO could prevent pial arteriolar dilation induced by oxidants. Therefore, it was very important to study the effect of DMSO on hemodynamics during CSD so that optimization of dose of DMSO as solvent can be made. STUDY DESIGN/MATERIALS AND METHODS: DMSO was topically applied on the exposed rat cortex. Single CSD was elicited by controlled injection of KCl. Pial arteriolar diameter, cerebral blood flow, and direct current potential during CSD were monitored by optical intrinsic signal imaging, laser speckle imaging, and electrophysiology method, respectively. RESULTS: Topical application of DMSO (0.1%, 0.4%, 2%, and 4%, v/v) increased arteriolar resting diameter and resting blood velocity at all vascular compartments. In addition, both vasodilation and hyperemic response to CSD were attenuated by DMSO in a dose-dependent manner at doses from 0.1% to 4%. In contrast, the maximum value of blood velocity during CSD was not significantly affected by DMSO. CONCLUSION: The attenuation in hemodynamic response during CSD could possibly be caused by increased baseline value of vessel tone and blood velocity. Our findings suggest that when investigators use DMSO to dissolve water-insoluble, topically applied drugs in the hemodynamic study of CSD, dose of DMSO should be kept below 0.1% in order to avoid false results.

Portable laser speckle perfusion imaging system based on digital signal processor.

The ability to monitor blood flow in vivo is of major importance in clinical diagnosis and in basic researches of life science. As a noninvasive full-field technique without the need of scanning, laser speckle contrast imaging (LSCI) is widely used to study blood flow with high spatial and temporal resolution. Current LSCI systems are based on personal computers for image processing with large size, which potentially limit the widespread clinical utility. The need for portable laser speckle contrast imaging system that does not compromise processing efficiency is crucial in clinical diagnosis. However, the processing of laser speckle contrast images is time-consuming due to the heavy calculation for enormous high-resolution image data. To address this problem, a portable laser speckle perfusion imaging system based on digital signal processor (DSP) and the algorithm which is suitable for DSP is described. With highly integrated DSP and the algorithm, we have markedly reduced the size and weight of the system as well as its energy consumption while preserving the high processing speed. In vivo experiments demonstrate that our portable laser speckle perfusion imaging system can obtain blood flow images at 25 frames per second with the resolution of 640 × 480 pixels. The portable and lightweight features make it capable of being adapted to a wide variety of application areas such as research laboratory, operating room, ambulance, and even disaster site.