Directly measuring absolute flow speed by frequency-domain laser speckle imaging

Laser speckle contrast imaging (LSCI) is a simple yet powerful tool to image blood flow. However, traditional LSCI has limited quantitative analysis capabilities due to various factors affecting flow speed evaluation, including illumination intensity, scattering from static tissues, and mathematical complexity of blood flow estimation. Here, we present a frequency-domain laser speckle imaging (FDLSI) method that can directly measure absolute flow speed. In phantom experiments, the measured flow speed agreed well with the preset actual values (10% deviation). Furthermore, in vivo experiments demonstrated that FDLSI was minimally affected by illumination condition changes.