Improving imaging depth by dynamic laser speckle imaging and topical optical clearing for in vivo blood flow monitoring

Laser speckle contrast imaging (LSI) is a promising non-invasive full-field blood flow monitoring technique. However, it is still far from clinic practice due to insufficient contrast-to-noise ratio (CNR) and limited detection depth. In this study, an in vivo laser speckle imaging visualization system was constructed to observe the blood circulation on a dorsal skin. A dynamic laser speckle imaging (dLSI) scheme, other than traditional laser speckle contrast analysis method, was applied to separate the dynamic light scattering from the static one to increase the image CNR. Based on the theoretical optimization for dLSI, at least two pixels are required for speckle pattern sampling and a spatial window size of 7 × 7 was optimal to balance the spatial resolution and statistical accuracy. The in vivo experiment observation shows that the CNR is improved 8.4 times by dLSI. The blood vessels were more pronounced, and more capillaries can be observed than in traditional laser speckle contrast images. Topical optical clearing technique by thiazone was combined with dLSI to increase the sampling depth from 700 to 1000 μm.