Abstract. We present a quantitative study of depolarization in biological tissues and correlate it with measured optical properties (reduced scattering and absorption coefficients). Polarized light imaging was used to examine optically thick samples of both isotropic (liver, kidney cortex, and brain) and anisotropic (cardiac muscle, loin muscle, and tendon) pig tissues in transmission and reflection geometries. Depolarization (total, linear, and circular), as derived from polar decomposition of the measured tissue Mueller matrix, was shown to be related to the measured optical properties. We observed that depolarization increases with the transport albedo for isotropic and anisotropic tissues, independent of measurement geometry. For anisotropic tissues, depolarization was higher compared to isotropic tissues of similar transport albedo, indicating birefringence-caused depolarization effects. For tissues with large transport albedos (greater than ∼0.97), backscattering geometry was preferred over transmission due to its greater retention of light polarization; this was not the case for tissues with lower transport albedo. Preferential preservation of linearly polarized light over circularly polarized light was seen in all tissue types and all measurement geometries, implying the dominance of Rayleigh-like scattering. The tabulated polarization properties of different tissue types and their links to bulk optical properties should prove useful in future polarimetric tissue characterization and imaging studies.

Formalin fixation is a preparation method widely used in handling tissue specimens, such as biopsies, specifically in optical studies such as microscopy. In this note, we examine how formalin fixation affects the polarization properties of porcine myocardium and liver as assessed by optical polarimetry. Spatial maps of linear retardance and depolarization were derived from four myocardial and four liver samples before and after formalin fixation. Overall, linear retardance and depolarization increased after fixation for both myocardium (15% and 23% increase, respectively) and liver (38% and 51%, respectively). The relative increase in retardance was greater in liver compared to myocardium, although the absolute increase in retardance was comparable for both. The effect of fixation on bulk optical properties was also investigated for myocardium where the scattering coefficient increased from 92 to 132 cm(-1) and the absorption coefficient remained constant at 1.1 cm(-1).