Characterization of Biological Tissues by Polarization Analysis of diffused light

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The scattering properties of a tissue depend on the cell size, cell constituents and cell structure ; therefore, the measurement of scattering light can be useful for tissue characterization, metabolism monitoring and so on. In particular, backscattering is very sensitive to both the size of the subcellular structure and the polarization state. The conventional method employed to study the scattering from biological material involves goniophotometric measurement ; however, the sample for this method should be very thin. Because biological tissues have very strong scattering properties and incident polarized beam becomes diffusive light while passing through very short path.This project aims to propose new method to obtain the 2D angular pattern of polarized backscattering light from small volume of turbid media such as living tissue without pretreatment. The system derives a single scattering component that has a specific angular distribution pattern depending on the constituents and s … More tructures of the scattering substances. We attempt to detect the angular distribution of the backscattered light by using a 2D imaging sensor. We developed a Monte Carlo simulation to estimate the photon propagation behavior of our experimental system. This simulation employed Mie scattering phase function and the results were normalized with incident beam power. The simulation results showed that the characteristic patterns, which contain information on the scattering particles and medium, are due to the scattering phenomenon that occurs only in a very small volume around the incident point. Moreover, the reduced scattering coefficient μs' served as a suitable index for estimating the influence of diffusive multiple scattering on the 2D pattern. The small pinhole system enables the suppression of the diffusive multiple scattering; therefore, the angular distribution of the informative single scattering component can be observed as a 2D image by using our system. We developed a basic experimental system that could obtain the 2D angular pattern of backscattering, and preliminary experiments using suspensions of polystyrene sphere in water were performed. We verified that the proposed system could obtain the 2D angular pattern of backscattered polarized light from even high scattering materials, with a μs' value of 1 mm^<-1>, which was equivalent to that obtained from biological materials. However, difference of intensity due to polarization direction was not clear compare to the predictions by the simulation. The reason of this discrepancy remains unsolved yet. In order to apply our method for tissue characterization, the experimental system should be improved further and new approaches to relate the 2D patterns of angular distribution to the tissue structure and constituents are required. Less