Verification of a two-layer inverse Monte Carlo absorption model using multiple source-detector separation diffuse reflectance spectroscopy

Manu Sharma,Mia K Markey,James W Tunnell,Ricky Hennessy

doi:10.1364/boe.5.000040

Abstract

A two-layer Monte Carlo lookup table-based inverse model is validated with two-layered phantoms across physiologically relevant optical property ranges. Reflectance data for source-detector separations of 370 μm and 740 μm were collected from these two-layered phantoms and top layer thickness, reduced scattering coefficient and the top and bottom layer absorption coefficients were extracted using the inverse model and compared to the known values. The results of the phantom verification show that this method is able to accurately extract top layer thickness and scattering when the top layer thickness ranges from 0 to 550 μm. In this range, top layer thicknesses were measured with an average error of 10% and the reduced scattering coefficient was measured with an average error of 15%. The accuracy of top and bottom layer absorption coefficient measurements was found to be highly dependent on top layer thickness, which agrees with physical expectation; however, within appropriate thickness ranges, the error for absorption properties varies from 12-25%.

Highlights

Diffuse reflectance spectroscopy (DRS) has been used to noninvasively measure tissue properties for skin-related disease diagnosis [1,2,3,4,5]
We present a two-layer Monte Carlo model for skin applications which offers increased utility compared to existing two-layer models as prior knowledge of the top layer thickness is not required
We show that the use of multiple source-detector separation (SDS) increases the range of values where we can accurately predict top layer thickness

Summary

Introduction

Diffuse reflectance spectroscopy (DRS) has been used to noninvasively measure tissue properties for skin-related disease diagnosis [1,2,3,4,5]. The delivered light is both scattered and absorbed by the tissue and is detected by another fiber, which is at a certain distance, known as the source-detector separation (SDS), from the source fiber. An accurate model of light transport in tissue is needed to relate the measured reflectance to tissue optical properties. One method for analyzing diffuse reflectance spectra is the diffusion approximation of the radiative transport equation; the diffusion approximation is not valid for short source-detector separations or in highly absorbing tissues [6,7,8]

Methods

Results

Conclusion