Contrast improvement in scattered light confocal imaging of skin birefringent structures by depolarization detection

Abstract

Here we describe a method for enhancing the contrast in imaging skin birefringent structures. The method relies on polarization-dependent optical properties and is implemented using cross polarized confocal microscopy. The experimental data obtained using ex-vivo and in-vivo measurements on human scalp hairs and human skin demonstrate a significant dependence of the change in polarization of light that interacted with the birefringent hair on the orientation of the incident polarization. The polarization dependent contrast, defined as the ratio of intensity measured for different orientations of the incident polarization when observed using cross polarized confocal microscopy furthermore depends on the hair type/degree of pigmentation and on the focusing depth inside the hair. No such dependence was observed for the upper skin layers, including the stratum corneum and epidermis. We propose a new method for enhancing the contrast between the skin and the birefringent hair by the use of cross polarized confocal microscopy combined with the variation of the polarization of the incoming light. Potential applications of this method include imaging of hairs for assessing the efficacy of hair removal methods and measurement of skin birefringence. The underestimation of the birefringence content resulting from the orientation related effects associated with the use of linearly polarized light for imaging tissues containing wavy birefringent structures could be minimized by this method.