Noninvasive determination of fiber orientation and tracking 2-dimensional deformation of human skin utilizing spatially resolved reflectance of infrared light measurement in vivo

Abstract

We propose a noninvasive method for determining Langer’s tension lines and tracking two-dimensional (2D) deformation of human skin utilizing spatially resolved diffuse reflectance (SRDR) of infrared (IR) light measurement in vivo. The anisotropic light propagation pattern of the skin was measured at several locations on the human body; then, the principal axis (i.e., eigenvector) of the radial plot of equi-distant intensity lines was obtained to determine the orientation of the scattering-induced anisotropic reflectance of IR light. The results indicate the proposed method is able to determine preferential orientation of filamentous fiber with a reasonable degree of prediction accuracy over the entire body. We validated the proposed method by comparing the detected orientations of fiber with a previous scattering model-based light propagation anisotropy analysis method. We measured temperature dependence and tensile stress-induced changes of the spatially resolved reflectance of IR light on the skin. The surface temperature affects the light transmittance almost isotopically on the propagation patterns. The main contribution of this work is tracking the direction of tension causing 2D deformation of human skin without visible markers. The proposed method is applicable to sensing facial gestures or skin movements induced by human motion of skeletal or facial muscles.