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The determination of scattering phase function as a microscopic basic tissue-optic parameter is very important for the theoretical description and practical realization of optical tomography in biomedical engineering. Right now there are only a few publications containing experimental data, measuring arrangements or even theoretical explanations for the realistic scattering phase functions of biological tissue. This is probably due to the very complex structure of biological specimen and some difficulties with the experimental setup. For the important field of radiation propagation simulations the analytical Henyey-Greenstein phase function has been assumed generally. But for the often used numerical modeling by the Monte-Carlo method an analytical representation of the angular scattering behavior is not required; sufficient are individual sample points. The determination of scattering phase functions of biological specimen is pretty difficult because of the several shapes, sizes, and concentrations of scatterers. But their distinguished consideration is necessary for the comparison with different theories of scattering, e.g. Mie theory. In particular the angular distribution of the scattered light intensity for a single scattering event has to be measured. Therefore the angular scattering distribution of tissues has to be evaluated as superpositioned individual scattering phase functions. The main problem with the instrumentation for investigating scattering phase functions is the need for generating and detecting the angular intensity distribution caused by single scattering events and its high dynamics. Because of the multiple scattering properties of tissues almost the entire object is illuminated often. But an intensity distribution caused by multiple scattering events could not represent the scattering phase function. Thus its contribution to the scattering distribution has to be suppressed. Therefore the detector's view field (i.e. the viewable solid angle with regard to the illuminated area) has to be limited to obtain a high angular resolution. This could be done for instance by controlling the detector's aperture, by introducing angular light wave guides or different techniques like polarization evaluation. Eventually the scattering location can be monitored by a built-in microscope.
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