Abstract: A device and clinical techniques that can help healthcare workers locate and image the general outlines of blood vessels that are located either under or near to tissue or skin surfaces are described. The device involves a substrate formed from a self-cooling polymeric matrix that incorporates at least a thermo-chromic colorant, and can provide a means to distinguish between different temperature regions when applied to a heat-emitting object or body. The device can be used in certain therapeutic or healthcare-related applications.