Analytical models for time-domain diffuse correlation spectroscopy for multi-layer and heterogeneous turbid media.

Jun Li,Chien-Sing Poon,Lina Qiu,Ulas Sunar

doi:10.1364/boe.8.005518

Abstract

A novel approach for time-domain diffuse correlation spectroscopy (TD-DCS) has been recently proposed, which has the unique advantage by simultaneous measurements of optical and dynamical properties in a scattering medium. In this study, analytical models for calculating the time-resolved electric-field autocorrelation function is presented for a multi-layer turbid sample, as well as a semi-infinite medium embedded with a small dynamic heterogeneity. To verify the analytical models, we used Monte Carlo simulations, which demonstrated that the theoretical prediction for the time-resolved autocorrelation function was highly consistent with the Monte Carlo simulation, validating the proposed analytical models. Using these analytical models, we also showed that TD-DCS has a higher sensitivity compared to conventional continuous-wave (CW) DCS for detecting the deeper dynamics. The presented analytical models and simulations can be utilized for quantification of optical and dynamical properties from future TD-DCS experimental data as well as for optimization of the experimental design to achieve maximum contrast for deep tissue dynamics.

Highlights

Diffuse correlation spectroscopy (DCS) is an optical technique utilizing the scattering feature of coherent light to probe the dynamical properties of a scattering medium [1,2,3,4,5,6,7]
2.2 time-domain diffuse correlation spectroscopy (TD-DCS) analytical model for a semi-infinite medium embedded with a small dynamic heterogeneity
We have presented analytical expressions for the time-resolved electric-field autocorrelation function for a multi-layer homogeneous turbid media as well as for a semi-infinite medium embedded with a small dynamic heterogeneity

Summary

Introduction

Diffuse correlation spectroscopy (DCS) is an optical technique utilizing the scattering feature of coherent light to probe the dynamical properties of a scattering (or turbid) medium [1,2,3,4,5,6,7]. Apart from the laser source, all the other optoelectronic components in this TD-DCS system were very similar to those used in a typical time-resolved spectroscopy (TRS) measurement This approach is mostly compatible with commonlyused TRS systems, enabling simultaneous measure of optical parameters of absorption and scattering coefficients and dynamic parameter of scattering particle diffusion coefficient. Reflectance geometry is widely adopted in biomedical applications such as brain function monitoring, in which the source and detector are located on the same surface of the sample For this geometry, the commonly used models include homogeneous semiinfinite and multi-layer models as well as a perturbation model in which a small dynamic heterogeneity embedded in a semi-infinite turbid medium [4,5,8]. We demonstrate that these analytical expressions and Monte Carlo simulations can allow optimizing future experimental protocols for improved depth selectivity

Analytical model for TD-DCS

TD-DCS in a multi-layer turbid sample

Verification of the analytical model with the Monte Carlo simulation

Simulation with a 3-layer model

Findings

Discussion and conclusion