Characterization of Turbid Media Using Stokes and Mueller-Matrix Polarimetry

Abstract

In this thesis we present the application of polarized light to characterize porcine liver and phantoms with matched bulk optical properties, correlate the depolarization of tissues with transport albedo and evaluate the severity of liver injury. We have used the Mueller matrix analysis and polar decomposition method for extraction of individual polarization properties in this thesis. We investigated the polarization properties of thick samples (1 cm) of porcine liver, intralipid phantoms and polystyrene micro-spheres phantoms with matched bulk optical properties. Significant depolarization differences between porcine liver and phantoms are observed. Contrary to previously reported results for transmission geometry, our results show the enhanced polarization preservation for porcine liver tissues as compared to fabricated phantoms, particularly in the backscattering detection geometry. Moreover, the intralipid phantoms, polarization behavior is well- approximated with liver tissue as compared to the polystyrene sphere phantoms. Polarized light imaging was employed to investigate the correlation between light depolarization and transport albedo for six different isotropic and anisotropic thick tissues in both transmission and backscattering mode. Total, linear and circular depolarization rates were observed to be dependent on the measured transport albedos, where depolarization increases with transport albedo for all type of tissues independent of detection geometries. Higher depolarization rates were observed for anisotropic tissues as compared to isotropic ones for comparable transport albedos, demonstrating the birefringence-caused depolarization in addition to scattering-caused depolarization. The ex vivo severity assessment of different liver injuries induced by carbon tetra chloride (CCl4) was probed by polarized light in the visible spectral range. Less injured liver samples show higher linear retardance as compared to normal liver tissue, while worse injuries correspond to almost no retardance. Fibrosis is the likely cause at less severe injuries results in higher observed linear retardance whereas more serious injuries destroy any kind of organization and hence yield no retardance. Furthermore, total- linear- and circular-depolarizations were observed to decrease with increased injuries. Most likely causes include change of transport albedo and relative refractive index of extracellular matrix.