Influence of perfusion depth on laser Doppler flow measurements with large source–detector spacing

Laser Doppler flowmetry with a large source–detector spacing has been applied to measure blood perfusion in the deeper regions of tissue. The influence of the depth of perfusion on the Doppler spectrum for the large source–detector spacing is likely to be different from that for the conventional laser Doppler instruments with small source–detector spacing. In this study, the light propagation in a tissue model with a blood perfusion layer is predicted by the Monte Carlo simulation to discuss the influence of the depth of perfusion, blood volume, and source–detector spacing on the spectrum of the Doppler signal detected with large source–detector spacing. The influence of the depth of perfusion on the Doppler spectrum for the large source–detector spacing is different from that for the conventional laser Doppler instruments with small source–detector spacing, although the influence of source–detector spacing and blood volume on the Doppler spectrum for large source–detector spacing is almost the same as that for the conventional laser Doppler instruments. The influence of the depth of the perfusion on the Doppler spectrum depends on the path length that the detected light travels at different depths.