DEPTH PROFILING OF LASER-HEATED CHROMOPHORES IN BIOLOGICAL TISSUES BYPULSED PHOTOTHERMAL RADIOMETRY

A solution method is proposed to the inverse problem of determining th e unknown initial temperature distribution in a laser-exposed test mat erial from measurements provided by infrared radiometry. A Fredholm in tegral equation of the first kind is derived that relates the temporal evolution of the infrared signal amplitude to the unknown initial tem perature distribution in the exposed test material. The singular-value decomposition is used to demonstrate the severely ill-posed nature of the derived inverse problem. Three inversion methods are used to esti mate solutions for the initial temperature distribution. A nonnegative ly constrained conjugate-gradient algorithm using early termination is found superior to unconstrained inversion methods and is applied to i mage the depth of laser-heated chromophores in human skin.