Laser Speckle Contrast Imaging (LSCI) plays an important role in studying blood flow, but suffers from limited penetration depth of light in turbid tissue. The strong scattering of tissue obviously reduces the image contrast which decreases the sensitivity to flow velocity. Some image processing or optical clearing methods have been proposed to lessen the deficiency, but quantitative assessment of improvement is seldom given. In this study, LSCI was applied to monitor the blood flow through a capillary embedded within various tissue phantoms at depths of 0.25, 0.45, 0.65, 0.85 and 1.05 mm, and the flow velocity in capillary was controllable from 0 to 4 mm/s. Here, glycerol, a common optical clearing agent, was mixed with Intralipid at different volume ratio to make the reduced scattering coefficient of tissue phantom decrease from 13.00 to 0.50 cm-1. The quantitative analysis demonstrates that the optical clearing method can obviously enhance the image contrast, imaging depth, and sensitivity to blood flow velocity. Comparing the Laser Speckle Contrast Analysis methods and the optical clearing method, we find that for typical turbid tissue, the sensitivity to velocity estimated by the Laser Speckle Temporal Contrast Analysis (LSTCA) is twice of that by the Laser Speckle Spatial Contrast Analysis (LSSCA); while the sensitivity to velocity estimated by using the two analysis methods has a 10-fold increase, respectively, if addition of glycerol makes the reduced scattering coefficient of tissue phantom decrease by 30%. Combining the LSTCA and the optical clearing method, the sensitivity to flow velocity will be further enhanced.
Nephron blood flow dynamics measured by laser speckle contrast imaging
