Noninvasive light-reflection technique for measuring soft-tissue stretch

A novel, to our knowledge, sensor for measuring the stretch in soft tissues such as skin is described. The technique, which is a modification of two-d imensional polarization imaging, uses changes in the reflectivity of polari zed light as a monitor of skin stretch. Measurements show that the reflecti vity increases with stretch. Measurements were made on guinea pig skin and on nonbiological materials. The changes in reflectivity result from the cha nges that take place in the interface roughness between skin or material la yers and the consequential changes in the diffuse reflective characteristic s of the skin. Conceptually, as the roughness of an interface decreases, a smoother reflecting interface is produced, resulting in a commensurate incr ease in specular reflection. A simple roughness model correctly predicts th e main experimental results. Results can be extended easily to real-time st retch analysis of large tissue areas that would be applicable for predictin g stresses in skin during and after the surgical closure of wounds. (C) 199 9 Optical Society of America.