Abstract
We present a Monte Carlo (MC) method to determine depth-dependent probability distributions of photon visitation and detection for optical reflectance measurements performed in the spatial frequency domain (SFD). These distributions are formed using an MC simulation for radiative transport that utilizes a photon packet weighting procedure consistent with the two-dimensional spatial Fourier transform of the radiative transport equation. This method enables the development of quantitative metrics for SFD optical sampling depth in layered tissue and its dependence on both tissue optical properties and spatial frequency. We validate the computed depth-dependent probability distributions using SFD measurements in a layered phantom system with a highly scattering top layer of variable thickness supported by a highly absorbing base layer. We utilize our method to establish the spatial frequency-dependent optical sampling depth for a number of tissue types and also provide a general tool to determine such depths for tissues of arbitrary optical properties.
Highlights
The use of spatial frequency domain (SFD) methods for diffuse optical imaging of biological tissues has gained significant traction in the biophotonics community since its introduction in 1998.1 SFD methods combine a measurement of spatially modulated reflectance at multiple spatial frequencies with light transport models to determine optical and physiological properties of the tissue in question
The power of SFD methods is demonstrated most notably in spatial frequency domain imaging (SFDI), where such measurements are made for every pixel in a wide-field image
We provide results of SFD measurements performed on this two-layer phantom system with differing thicknesses of the top layer for comparison with the Monte Carlo (MC) simulation results
Summary
The use of spatial frequency domain (SFD) methods for diffuse optical imaging of biological tissues has gained significant traction in the biophotonics community since its introduction in 1998.1 SFD methods combine a measurement of spatially modulated reflectance at multiple spatial frequencies with light transport models to determine optical and physiological properties of the tissue in question. Understanding the spatial regions that detected photons have sampled, and their sensitivity to source–detector configuration, is crucial in many situations, including the assignment of optical properties to a given tissue volume, accounting for the effects of tissue heterogeneities, measuring layered tissues, and the performance of image reconstruction. While this problem has been extensively studied for spatially/temporally resolved and temporal frequency domain methods,[4,5,6,7,8,9,10,11,12,13,14,15,16] extensive quantitative
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