An apparatus for direct determination of the spectrally resolved scattering phase function of suspensions and emulsions is described. The system has a polychromatic xenon lamp as light source and a spectrometer as detector. In combination with a stepper motor the system enables sepctrally and angularly resolved measurements in the range of 450nm to 950nm and 10° to 170°, respectively. A post processing algorithm, which takes the light propagation inside the cuvette within the regime of single scattering and the spectral dimension into account, was developed. This allows a direct determination of the scattering phase function for the indicated spectral and angular range. By comparing measurements on polystyrene microspheres with Mie theory the concept of the presented instrument was validated. Finally, the method was used to determine the scattering phase functions of different types and brands of soybean oil emulsions, a common phantom material in the field of diffuse optics.
A method to correct for surface scattering in spatial frequency domain imaging (SFDI) is presented. The use of a modified analytical solution of the radiative transfer equation allows calculation of the reflectance and the phase of a rough semi-infinite geometry so that both spatial frequency domain reflectance and phase can be applied for precise retrieval of the bulk optical properties and the surface scattering. For validation of the method, phantoms with different surface roughness were produced. Contrarily, with the modified theory, it was possible to dramatically reduce systematic errors due to surface scattering. The evaluation of these measurements with the state-of-the-art theory and measuring modality, i.e., using crossed linear polarizers, reveals large errors in the determined optical properties, depending on the surface roughness, of up to ≈100 % . These results were confirmed with SFDI measurements on a phantom that has a structured rough surface.
Utilizing a modified analytical solution of the radiative transfer equation allows to fit both the spatial frequency domain reflectance and the phase. The additional information then allows to correct for surface reflections.
We demonstrate optical phantom experiments on the phase function parameter γ using spatial frequency domain imaging. The incorporation of two different types of scattering particles allows for control of the optical phantoms’ microscopic scattering properties. By laterally structuring areas with either TiO2 or Al2O3 scattering particles, we were able to obtain almost pure subdiffusive scattering contrast in a single optical phantom. Optical parameter mapping was then achieved using an analytical radiative transfer model revealing the microscopic structural contrast on a macroscopic field of view. As part of our study, we explain several correction and referencing techniques for high spatial frequency analysis and experimentally study the sampling depth of the subdiffusive parameter γ.
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.
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.
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.
Spectrally and angular resolved light scattering from yeast cells was studied with a scattering microscope and a goniometer. Different cell models were investigated with help of analytical solutions of Maxwell's equations. It was found that extraction of precise morphological and optical cellular properties from the measured scattering patterns and phase functions requires more sophisticated cell models than standard Mie theory.
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