Steady-state directional diffuse reflectance and fluorescence of human skin

We present numerical simulations predicting the directional diffuse reflectance and autofluorescence from human skin. Skin is modeled as a seven-layered medium, with each layer having its own optical properties and fluorophore concentrations. Both collimated and diffuse monochromatic excitation at 442 nm are considered. In addition, the effect of an index-matching cream used to eliminate total internal reflection within the skin is assessed. We compute the intensity distributions of the excitation and fluorescence light in the skin by solving the radiative transfer equation using the modified method of characteristics. It was found that the use of an index-matching cream reduces the directional fluorescence signal while increasing the directional diffuse reflectance from the skin for collimated excitation. On the other hand, both the fluorescence and diffuse reflectance increase for diffuse excitation with an index-matching cream. Moreover, the directional fluorescence intensity obtained by use of collimated excitation is larger than that obtained by use of diffuse excitation light. This computational tool could be valuable in designing optical devices for biomedical applications.