| A non-invasive polarized light reflection measurement method to measure the stretch of soft tissue, such as skin, is described. The technique utilizes changes in the reflectivity of polarized light intensity as a monitor of skin stretch. Measurements on in-vitro pigskin and in-vivo human skin show that the reflectivity of polarized light intensity increases linearly with stretch over a range. The changes in diffusive reflectivity properties of skin result from the alterations that take place in the roughness across the thickness of the skin layers due to stretch. Conceptually, as the roughness of a layer decreases with stretch, a smoother reflecting media is produced resulting in a proportional increase in the specular reflection. Results can be easily extended to a real time stretch analysis of large tissue areas that would be applicable for mapping the stretch of skin. Simple one- and two-dimensional sinusoidal theoretical surface roughness model correctly predicts the experimental measurements. In-vitro pigskins were also used for the tissue burn experiments and its measured reflectivity slope versus stretch increases with the burn duration up to a limited thermal excitation. Above this limit, the in-vitro sample becomes optically transparent, as its biomechanical properties is thermally altered and a negative reflectivity slope is observed. |
