IMAGING LASER-HEATED SUBSURFACE CHROMOPHORES IN BIOLOGICAL-MATERIALS - DETERMINATION OF LATERAL PHYSICAL DIMENSIONS

We describe a non-contact method using infrared radiometry to determin e lateral physical dimensions of laser heated subsurface chromophores in biological materials. An imaging equation is derived that relates m easured radiometric temperature change to the reduced two-dimensional temperature increase of laser heated chromophores. From measured image s of radiometric temperature change, the lateral physical dimensions o f chromophores positioned in an in vitro model of human skin are deter mined by deconvolution of the derived imaging equation using a non-neg ative constrained conjugate gradient algorithm. Conditions for optimum spatial resolution are found by analysis of a derived radiometric tra nsfer function and correspond to superficial chromophores and/or weak infrared absorption in a laser irradiated biological material. Analysi s indicates that if the infrared attenuation coefficient is sufficient ly small (i.e., less than 10 mm(-1)), infrared radiometry in combinati on with a deconvolution algorithm allows estimation of lateral physica l dimensions of laser heated subsurface chromophores in human skin.