Entropy analysis reveals a simple linear relation between laser speckle and blood flow

Dynamic laser speckles contain motion information of scattering particles which can be estimated by laser speckle contrast analysis (LASCA). In this work, an entropy-based method was proposed to provide a more robust estimation of motion speed. An in vitro flow simulation experiment confirmed a simple linear relation between entropy, exposure time, and speed. A multimodality optical imaging setup is developed to validate the advantages of the entropy method based on laser speckle imaging, green light imaging, and fluorescence imaging. The entropy method overcomes traditional LASCA with less noisy interference, and extracts more visible and detailed vasculatures in vivo. Furthermore, the entropy method provides a more accurate estimation and a stable pattern of blood flow activations in the rat's somatosensory area under multitrial hand paw stimulations.