Biomedical subjects

Margarita L Shendeleva

Publications and source records attributed to Margarita L Shendeleva.

4 recordsLinked to original sources

PubMed2006

Diffuse light propagation in a turbid medium with varying refractive index: Monte Carlo modeling in a spherically symmetrical geometry.

We report on the development of Monte Carlo software that can model media with spatially varying scattering coefficient, absorption, and refractive index. The varying refractive index is implemented by calculating curved photon paths in the medium. The results of the numerical simulations are compared with analytical solutions obtained using the diffusion approximation. The model under investigation is a scattering medium that contains a spherically symmetrical inclusion (inhomogeneity) created by variation in optical properties and having no sharp boundaries. The following steady-state cases are considered: (a) a nonabsorbing medium with a spherically symmetrical varying refractive index, (b) an inclusion with varying absorption and scattering coefficients and constant refractive index, and (c) an inclusion with varying absorption, scattering, and refractive index. In the latter case it is shown that the interplay between the absorption coefficient and the refractive index may create the effect of a hidden inclusion.

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PubMed2004

Green functions for diffuse light in a medium comprising two turbid half-spaces.

A review of Green functions for diffuse light in two semi-infinite scattering and absorbing half-spaces separated by a plane interface is presented. The frequency-domain Green functions for an intensity-modulated point source are derived within the diffusion approximation by the Hankel transform with respect to the variable in the plane of the interface. Green functions for a line source and a plane source parallel to the interface are obtained from the three-dimensional Green functions by the method of descent. Green functions for a steady state are obtained as a limit of zero modulation frequency. Connection of the frequency-domain Green functions with the time-domain Green functions is shown by use of the Fourier transform in time. The influence of the relative optical parameters, namely, the ratios of diffusion coefficients, absorption coefficients, and refractive indices of the two media on the shape of the contour lines of the specific intensity, is shown for the continuous and intensity-modulated point sources.

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PubMed2004

Green functions for diffuse photon-density waves generated by a line source in two nonabsorbing turbid media in contact.

Diffuse photon-density waves generated by an instantaneous line source that is parallel to the interface between two semi-infinite turbid media are studied by use of the diffusion approximation. For two nonabsorbing media the Green functions for diffuse light are obtained based on the Green functions for temperature fields that were derived with the Cagniard-de Hoop method. The boundary conditions for diffuse light take into account the discontinuity in the specific intensity at the interface between two media with different refractive indices. The results of the calculations of the specific intensities and the gradient lines for different sets of parameters are presented.

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PubMed2004

Radiative transfer in a turbid medium with a varying refractive index: comment.

In the literature one can encounter at least two different radiative transfer equations for media with spatially varying refractive indices. These are the results of Ferwerda [J. Opt. A Pure Appl. Opt. 1, L1 (1999)] and Tualle and Tinet [Opt. Commun. 228, 33 (2003)]. Accordingly, two different diffusion approximations are derived from these two radiative transfer equations. I reconsider the derivation of the radiative transfer equation in a medium with an inhomogeneous refractive index and confirm the result of Tualle and Tinet. In the diffusion approximation, a simple analytical solution has been found for the steady-state illumination of a non-absorbing turbid medium with a varying refractive index.

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