Browsing by Author "Matcher, S. J."
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Item Open Access Analysis of the Spatial Distribution of Detector Sensitivity in a Multilayer Randomly Inhomogeneous Medium with Strong Light Scattering and Absorption by the Monte Carlo Method.(Springer Science Business Media, 2001-10-01T00:00:00Z) Meglinski, I. V.; Matcher, S. J.The spatial distribution of sensitivity in the domain of detection of a fiber- optic sensor used for spectrophotometric studies of skin and other biological tissues is studied. The method and results of modeling the propagation of optical radiation in multilayer randomly inhomogeneous media with strong light scattering and absorption are presented. Owing to the small distances between the source and detector (100–800 µm), the propagation of radiation in the medium under study is modeled by the Monte Carlo method combining the calculation of true paths and the use of statistical weights. For the same reason, we represent the surface and interfaces of layers of skin as rough randomly periodic surfaces corresponding to the actual structure of human skin. The method presented can be recommended as a means for the optimum selection of an arrangement for radiation incoupling and outcoupliItem Open Access Computer simulation of the skin reflectance spectra(Elsevier Science B.V., Amsterdam., 2003-02-01T00:00:00Z) Meglinski, I. V.; Matcher, S. J.The reflectance spectra of the human skin in visible and near-infrared (NIR) spectral region have been calculated using the Monte Carlo technique, and the specular and internal reflection on the medium surface is taken into account. Skin is represented as a complex inhomogeneous multi-layered highly scattering and absorbing medium. The model takes into account variations in spatial distribution of blood, index of blood oxygen saturation, volume fraction of water and chromophores content. The simulation of the skin tissues optical properties and skin reflectance spectra are discussed. Comparison of the results of simulation and in vivo experimental results are given.Item Open Access Modeling the sampling volume for the skin blood oxygenation measurements(Springer Science Business Media, 2001-01-01T00:00:00Z) Meglinski, I. V.; Matcher, S. J.Abstract The absolute quantified measurement of haemoglobin skin blood saturation from collected reflectance spectra of the skin is complicated by the fact that the blood content of tissues can vary both in the spatial distribution and in the amount. These measurements require an understanding of which vascular bed is primarily responsible for the detected signal. Knowing the spatial detector depth sensitivity makes it possible to find the best range of different probe geometries for the measurements of signal from the required zones and group of vessels inside the skin. To facilitate this, a Monte Carlo simulation has been developed to estimate the sampling volume offered by fibre-optic probes with a small source-detector spacing (in the current report 250 μm, 400 μm and 800 μm). The optical properties of the modelled medium are taken to be the optical properties of the Caucasian type of skin tissue in the visible range of the spectrum. It is shown that, for a small source-detector separation (800 μm and smaller), rough boundaries between layers of different refractive index can play a significant role in skin optics. Wavy layer interfaces produce a deeper and more homogeneous distribution of photons within the skin and tend to suppress the direct channelling of photons from source to detector. The model predicts that a probe spacing of 250 μm samples primarily epidermal layers and papillary dermis, whereas spacings of 400–800 μm sample upper blood net dermis andItem Open Access Monte Carlo modeling of polarized light propagation in biological tissues.(Springer Science Business Media, 2004-01-01T00:00:00Z) Gangnus, S. V.; Matcher, S. J.; Meglinski, I. V.The application of polarization-sensitive optical coherence tomography (PS-OCT) creates new possibilities for biomedical imaging. In this work, we present a numerical simulation of the signal from a PS-OCT interferometer. We explore the possibility to retrieve information concerning the optical birefringence properties of multiple layered tissues from the depth-resolved PS-OCT interferometric signal in the presence of strong elastic light scattering. Our simulation is based on a Monte Carlo algorithm for the propagation of polarized light in a birefringent multiple scattering medium. Confocal and time-gated detection are also included. To describe the polarization state of light, we use the Jones formalism, which reduces the calculation time compared with the full Stokes-Müller formalism. To analyse the polarization state of the partially polarized back-scattered light, we applied a standard method using the Stokes vector, which is derived from the Jones vector. In this work, we examined the Stokes vector variations with depth for different tissue types. The oscillations of the Stokes vector are clearly demonstrated in the case of a uniform birefringent medium. We also investigated a two-layered tissue with a different birefringence of each layer. The Stokes vector variation with depth is compared to the uniform case and used to assess the depth-sensitivity of PS-OCT. Our simulation results are also compared with published experimental results of other groupsItem Open Access Quantitative assessment of skin layers absorption and skin reflectance spectra simulation in the visible and near-infrared spectral regions(Iop Publishing, 2002-11-01T00:00:00Z) Meglinski, I. V.; Matcher, S. J.We have simulated diffuse reflectance spectra of skin by assuming a wavelength- independent scattering coefficient for the different skin tissues and using the known wavelength dependence of the absorption coefficient of oxyand deoxyhaemoglobin and water. A stochastic Monte Carlo method is used to convert the wavelength-dependent absorption coefficient and wavelengthindependent scattering coefficient into reflected intensity. The absorption properties of skin tissues in the visible and near-infrared spectral regions are estimated by taking into account the spatial distribution of blood vessels, water and melanin content within distinct anatomical layers. The geometrical peculiarities of skin histological structure, degree of blood oxygenation and the haematocrit index are also taken into account. We demonstrate that when the model is supplied with reasonable physical and structural parameters of skin, the results of the simulation agree reasonably well with the results of in vivo measurements of skin spectra.