Monte Carlo simulation platform for laser Doppler flowmetry

Monte Carlo simulation of light propagation in turbid media is important in biomedical optics. Most existing platforms simulate light-tissue interactions in backscattering and planar geometries and are voxel-based, which limits their ability to model curved boundaries accurately. Few platforms incorporate Doppler shifts from flowing media, and they allow limited customization of flow profiles and scattering properties. Although laser Doppler flowmetry (LDF) is common in backscattering-based tissue measurements or low-scattering through-transmission setups, the intermediate case of through-transmission measurements in more scattering samples is underexplored. This case is relevant for applications such as flow quantification in lab-on-a-chip systems and inline flow sensors for biological fluids.

To study flow in highly scattering samples (1 to $10{\mathrm{mm}}^{-1}$ ), we developed a voxel-free Monte Carlo simulation platform for through-transmission LDF: MC-Doppler. We compare simulated and experimental Doppler power spectra.

MC-Doppler uses unit vectors and ray tracing to model light propagation, with fully customizable scattering phase functions and flow fields. It was tested with various suspensions of differently sized polystyrene beads, at flow rates ranging from 0 to $15\mathrm{mL}/\min$ , within a 1 mm diameter glass tube.

Simulated and measured Doppler power spectra matched well for scattering coefficients up to $5{\mathrm{mm}}^{-1}$ . Mismatches between the spectra were found near $10{\mathrm{mm}}^{-1}$ .

MC-Doppler accurately simulates light propagation for through-transmission laser Doppler up to moderate scattering coefficients.