A need exists for the continued development of diagnostic tools and methods capable of distinguishing and characterizing slight differences in the optical properties of tissues. We present a method to estimate the scattering coefficient contribution as a function of particle size in complex mixtures of polystyrene spheres. The experimental method we used is a Mueller matrix imaging approach. The Mueller matrix encodes the polarization-dependent properties of the sample and describes how a given sample will transform an incident light polarization state. A partial least-squares approach is used to form a model around a set of Mueller matrix image-based measurements to accurately predict the individual scattering coefficient contributions in phantoms containing 0.2, 0.5, 1, and 2 µm-diameter polystyrene spheres. The results show individual scattering coefficient contribution errors as low as 0.1585 cm–1 can be achieved. In addition, it is shown how the scattering type (i.e., Rayleigh and Mie) is encoded within the Mueller matrix. Such methods may eventually lead to the development of improved diagnostic tools capable of characterizing and distinguishing between tissue abnormalities, such as superficial cancerous lesions from their benign counterparts.
In this paper we present experimental results demonstrating processing techniques developed in our laboratory that can be utilized to decode or extract useful information from two-dimensional Mueller matrices of turbid media. Through the use of these methods, involving the partial least squares technique, it is shown how scattering coefficient contributions as a function of particle size can be estimated for a given sample. Furthermore, we demonstrate how a spatial selection algorithm known as "chain select" can be used to help facilitate the interpretation of the measured Mueller matrix images. The samples utilized in this investigation were comprised of polystyrene spheres with diameters ranging from 200 nm to 2000 nm and analyzed with 514 nm light. At this wavelength, both Rayleigh and Mie-types of scattering are observed.
In the recent past, optical polarimetry has been shown as a potential method for noninvasive physiologic glucose sensing in the eye. Although the necessary sensitivity and accuracy have been demonstrated experimentally through in vitro studies using a range of media from simplistic glucose doped-water to more complex media such as aqueous humor, the main problem currently hindering long-term in vivo measurements is corneal birefringence coupled with motion artifact. This is due to the inability to distinguish E-field rotation due to glucose from the effects of time varying corneal birefringence. In this investigation, the effect of corneal birefringence will be discussed and a potential method to overcome this problem will be presented with supporting results.
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