A new epoxy-resin-based optical phantom system with adjustable subdiffusive scattering parameters is presented along with measurements of the intrinsic absorption, scattering, fluorescence, and refractive index of the matrix material. Both an aluminium oxide powder and a titanium dioxide dispersion were used as scattering agents and we present measurements of their scattering and reduced scattering coefficients. A method is theoretically described for a mixture of both scattering agents to obtain continuously adjustable anisotropy values g between 0.65 and 0.9 and values of the phase function parameter γ in the range of 1.4 to 2.2. Furthermore, we show absorption spectra for a set of pigments that can be added to achieve particular absorption characteristics. By additional analysis of the aging, a fully characterized phantom system is obtained with the novelty of g and γ parameter adjustment.
In this study the formation of a surface layer on top of an Intralipid dilution was studied. By use of spatial frequency reflectance and spatially resolved reflectance the surface layer could be characterized. The influence on the determination of the optical properties assuming a semi-infinite medium in the theory was investigated. By use of an angularly resolved reflectance device the formation even on a horizontally orientated glass slide could be shown.
We present an experimental characterization of an optical phantom system based on epoxy resin using two different kinds of scatterers: TiO2 and Al2O3. A combination of both scattering materials allows adjusting the anisotropy value of the phase function g or the phase function related parameter γ . As part of this work, both scattering agents are extensively studied.
Transmittance and reflectance from spruce wood and bovine ligamentum nuchae as two different fibrous media are examined by time-of-flight spectroscopy for varying source detector separations and several orientations of the fibers in the sample. The anisotropic diffusion theory is used to obtain the absorption coefficient and the diffusion coefficients parallel and perpendicular to the fibers. The results are compared to those obtained with the isotropic diffusion theory. It is shown that for increasing source detector separations, the retrieved optical properties change as expected from Monte Carlo simulations performed in a previous study. This confirms that the anisotropic diffusion theory yields useful results for certain experimental conditions.
The optical properties of the human head in the range from 600 nm to 1100 nm have been non-invasively in-vivo investigated by various research groups using different diffuse optics techniques and data analysis methods.
Time-resolved diffuse optical spectroscopy measurements of phantoms at small source-detector separations yield good results for the retrieved coefficients of reduced scattering and absorption when a hybrid Green’s function of the radiative transfer equation for semi-infinite media is used.
A semi-infinite space Green’s function of the time-dependent radiative transfer equation is derived based upon an exact solution for anisotropic scattering in infinite space and the approximated extrapolated boundary condition. The obtained solution is compared to Monte Carlo simulations and used for retrieving the optical parameters of simulated data in a nonlinear fit. It is shown that the solution performs well for boundaries with mismatched refractive indices. The relative errors in the fitted optical parameters are considerably smaller than by using the diffusion theory.
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