Abstract
The use of perturbation and differential Monte Carlo (pMC/dMC) methods in conjunction with nonlinear optimization algorithms were proposed recently as a means to solve inverse photon migration problems in regionwise heterogeneous turbid media. We demonstrate the application of pMC/dMC methods for the recovery of optical properties in a two-layer extended epithelial tissue model from experimental measurements of spatially resolved diffuse reflectance. The results demonstrate that pMC/dMC methods provide a rapid and accurate approach to solve two-region inverse photon migration problems in the transport regime, that is, on spatial scales smaller than a transport mean free path and in media where optical scattering need not dominate absorption. The pMC/dMC approach is found to be effective over a broad range of absorption (50 to 400%) and scattering (70 to 130%) perturbations. The recovery of optical properties from spatially resolved diffuse reflectance measurements is examined for different sets of source-detector separation. These results provide some guidance for the design of compact fiber-based probes to determine and isolate optical properties from both epithelial and stromal layers of superficial tissues.
Highlights
There has been significant interest in the noninvasive determination of the morphology and biochemical composition of biological tissues through the measurement of optical properties
This study demonstrated the use of pMC/dMC methods in conjunction with a gradient-based optimization algorithm to process MCsimulated spatially resolved frequency-domain reflectance measurements to provide for the efficient and rapid recovery of optical properties in a layered epithelial tissue model
We provide the results of optical property recovery from SRDR measurements made in 10 different phantoms where s is held fixed and the top layer a is varied between 50 and 400% of the background
Summary
There has been significant interest in the noninvasive determination of the morphology and biochemical composition of biological tissues through the measurement of optical properties. Epithelial tissues are a major target because they represent the site from which more than 85% of all cancers originate.[1] Epithelial tissues line organ surfaces with a single or stratified layer of closely packed cells and are supported by underlying stromal tissue composed primarily of collagen and other extracellular matrix proteins. It is well known that the vast majority of epithelial cancers are preceded by distinct biochemical and morphological changes in both the epithelia and stroma.[2] The thickness of the cellular epithelial layer is typically Շ500 m and lies within the transport regime with respect to optical scattering.[3,4] On one hand, the thickness of the cellular epithelium is of the same order or larger than the single scattering mean free path ls=1 / sof photons in the visible and near-IR, typically ls ϳ 5 to 100 m. When using light to interrogate both the epithelium and the underlying stroma, one will invariably detect photons that have multiply scattered within the tissue; often interacting with
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