Effects of formalin fixation on tissue optical polarization properties

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).