Laser speckle simulation for laser speckle contrast imaging

Abstract

Pulse waveform signals extracted from LSCI (Laser Speckle Contrast Imaging) time series in biological tissue are used to gain information about the vital signs of a person e.g. heart rate and respiration. This technic is also called speckle plethysmography (SPG) and has an advantage over its counterpart, photoplethysmography (PPG, used for pulse oximetry), as it is less sensitive to difference in skin tone. It is not fully understood how the difference in physical phenomena, like light absorption and scattering modulates the SPG and PPG. Here we propose a novel simulation which models the laser speckles observed in a biological tissue with a video camera where we include, camera exposure time, speckle motion with the blood flow as well as the speckle decorrelation time. In addition, we account for absorption and scattering by blood cells which we vary as a function of the blood flow. Using a conventional SPG algorithm, we obtain pulse waveforms which we compare to real measurements in the human finger. While a lot of parameters in the simulation originate from known quantities e.g. blood velocity in microvasculature of the finger, some simulation parameters such as absorption and scattering variation as well as the speckle decorrelation are variables which we can tune in our simulation. Therefore, by tuning the forementioned variables, we gain a better understanding in which bio-physical phenomenon has the most prevalent effect on the speckle dynamics and its consequences on the LSCI signal.