Abstract
.Significance: Definitive diagnostics of many diseases is based on the histological analysis of thin tissue cuts with optical white light microscopy. Extra information on tissue structural properties obtained with polarized light would help the pathologist to improve the accuracy of his diagnosis.Aim: We report on using Mueller matrix microscopy data, logarithmic decomposition, and polarized Monte Carlo (MC) modeling for qualitative and quantitative analysis of thin tissue cuts to extract the information on tissue microstructure that is not available with a conventional white light microscopy.Approach: Unstained cuts of human skin equivalents were measured with a custom-built liquid-crystal-based Mueller microscope in transmission configuration. To interpret experimental data, we performed the simulations with a polarized MC algorithm for scattering anisotropic media. Several optical models of tissue (spherical scatterers within birefringent host medium, and combination of spherical and cylindrical scatterers within either isotropic or birefringent host medium) were tested.Results: A set of rotation invariants for the logarithmic decomposition of a Mueller matrix was derived to rule out the impact of sample orientation. These invariants were calculated for both simulated and measured Mueller matrices of the dermal layer of skin equivalents. We demonstrated that only the simulations with a model combining both spherical and cylindrical scatterers within birefringent host medium reproduced the experimental trends in optical properties of the dermal layer (linear retardance, linear dichroism, and anisotropic linear depolarization) with layer thickness.Conclusions: Our studies prove that Mueller polarimetry provides relevant information not only on a size of dominant scatterers (e.g., cell nuclei versus subwavelength organelles) but also on its shape (e.g., cells versus collagen fibers). The latter is directly related to the state of extracellular collagen matrix, which is often affected by early pathology. Hence, using polarimetric data can help to increase the accuracy of diagnosis.
Highlights
Probing the tissue with polarized light has been proven to be an efficient approach for fast noninvasive tissue diagnostics
We found that only the optical model of the dermal layer, which includes both spheres and cylinders distributed in the birefringent host medium (SCB model), can reproduce the effects of anisotropic linear depolarization, linear dichroism, and linear retardance observed in our experiments
We used Monte Carlo (MC) software to model scattering of polarized light within the uniaxial birefringent scattering media and applied the logarithmic decomposition of simulated Mueller matrices to study a dependence of linear retardance, linear dichroism, and depolarization parameters on thickness in transmission configuration
Summary
Probing the tissue with polarized light has been proven to be an efficient approach for fast noninvasive tissue diagnostics. The interpretation of optical data and analytical prediction of the results of polarized light interaction with a biological tissue is not straightforward, as biological tissues are extremely complex objects containing a large number of randomly distributed multidisperse microscopic scatterers and anisotropic microstructures.[1] It has been shown that Mueller matrix formalism is a powerful tool in the study of biological samples.[2,3,4] This phenomenological approach describes the interaction of polarized light with a sample using a model of “equivalent optical circuit” built from the basic optical elements—diatenuators, retarders, and depolarizers. Since human skin equivalents can be produced with less variability compared with real human skin, these tissue models were chosen for our studies
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