Light diffusion in N-layered turbid media: frequency and time domains
ABSTRACT We deal with light diffusion in mismatched N-layered turbid media having a finite or an infinitely thick N'th layer. We focus on time-resolved light propagation in both the frequency and time domains. Based on our results for the steady-state domain, solutions of the N-layered diffusion equations in the frequency and time domains are obtained by applying the Fourier transform technique. Different methods for calculation of the inverse Fourier transform are studied to validate the solutions, showing relative differences typically smaller than 10(-6). The solutions are compared to Monte Carlo simulations, revealing good agreement. Finally, by applying the Laplace and Fourier transforms we derive a fast ( approximately 1 ms) and accurate analytical solution for the time domain reflectance from a two-layered turbid medium having equal reduced scattering coefficients and refractive indices in both layers.
Journal of Physics A Mathematical and Theoretical 06/2015; 48(22). DOI:10.1088/1751-8113/48/22/225201 · 1.69 Impact Factor
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ABSTRACT: We present a near-infrared spectroscopy (NIRS) approach for the optical characterization of two-layered tissuemimicking phantoms. For the data acquisition, we employed a multi-distance frequency-domain system. For the data analysis, we implemented an inversion routine based on a two-layered solution of the frequency-domain diffusion equation as the forward model. Measured quantities were the absorption and reduced scattering coefficients of the first layer (μa1, μ’s1) and the second layer (μa2, μ’s2), and the thickness of the first layer (L). We report measurements on three two-layered liquid phantoms featuring absorption coefficients in the range 0.009-0.017 mm-1, reduced scattering coefficients in the range 0.69-0.92 mm-1, and first layer thickness in the range 8-15 mm. Our method yielded measured values of the optical coefficients and first layer thickness (μa1, μ’s1, μa2, μ’s2, and L) that are within 10% of the true values (optical properties measured in the infinite geometry; and the true first layer thickness). These are promising results toward exploring the potential of this two-layered medium approach in the human head, where the two layers would represent extracerebral and cerebral tissue, respectively.Conference on Optical Tomography and Spectroscopy of Tissue X; 03/2013
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ABSTRACT: The pathogenic process of Alzheimer's disease (AD) begins years before clinical diagnosis. Here, we suggest a method that may detect AD several years earlier than current exams. The method is based on previous reports that relate the concentration ratio of biomarkers (amyloid-beta and tau) in the cerebrospinal fluid (CSF) to the development of AD. Our method replaces the lumbar puncture process required for CSF drawing by using fluorescence measurements. The system uses an optical fiber coupled to a laser source and a detector. The laser radiation excites two fluorescent probes which may bond to the CSF biomarkers. Their concentration ratio is extracted from the fluorescence intensities and can be used for future AD detection. First, we present a theoretical model for fluorescence concentration ratio estimation. The method's feasibility was validated using Monte Carlo simulations. Its accuracy was then tested using multilayered tissue phantoms simulating the epidural fat, CSF, and bone. These phantoms have various optical properties, thicknesses, and fluorescence concentrations in order to simulate human anatomy variations and different fiber locations. The method was further tested using ex vivo chicken tissue. The average errors of the estimated concentration ratios were low both in vitro (4.4%) and ex vivo (10.9%), demonstrating high accuracy. (C) 2014 Society of Photo-Optical Instrumentation Engineers (SPIE).Journal of Biomedical Optics 12/2014; 19(12):127007. DOI:10.1117/1.JBO.19.12.127007 · 2.75 Impact Factor