Estimating the Dependence of Differential Pathlength Factor on Blood Volume and Oxygen Saturation using Monte Carlo method

Abstract

Differential Pathlength Factor (DPF) is a vital parameter for the Beer-Lambert law based calculations in estimating tissue perfusion using non-invasive optical techniques. A significant error in the measured concentration of oxyhemoglobin and deoxyhemoglobin has been reported due to the usage of wrong DPF values. The dependence of DPF on blood oxygen saturation and blood volume has never been studied earlier. In this work, a Monte Carlo model of perfused skin tissue was developed and executed at 660 nm and 940 nm optical wavelengths at a reflectance geometry. DPFs were simulated through 1-10 mm source detector separations at different blood volumes and oxygen saturations. Results showed higher DPFs at lower wavelengths and considerable variation with blood volume and oxygen saturation.

Estimation of the Differential Pathlength Factor for Human Skin Using Monte Carlo Simulations

“…Thus, the actual optical pathlength is much larger than source-to-detector separation (optode spacing), and so the differential pathlength factor (DPF) was incorporated into the above equation to relate the actual optical pathlength to the source-to-detector separation [27,28]. Many studies have estimated the optical pathlength and the DPF computationally or experimentally [27][28][29][30]. Studies have shown that the DPF can be estimated directly from direct time-of-flight measurements [27].…”

“…Phase-resolved optical spectroscopy has also been utilized to estimate the DPF [29,31]. Computationally, the Monte Carlo method was utilized to estimate the DPF in reflectance photoplethysmography [28] and blood volume and oxygen saturation [30] for two wavelengths. Moreover, researchers have investigated the DPF's dependence on optode spacing, operating wavelength, and age [32,33].…”