We have combined two optical techniques to enable simultaneous assessment of structure and composition of human
skin in vivo: Pulsed photothermal radiometry (PPTR), which involves measurements of transient dynamics in midinfrared
emission from sample surface after exposure to a light pulse, and diffuse reflectance spectroscopy (DRS) in
visible part of the spectrum. Namely, while PPTR is highly sensitive to depth distribution of selected absorbers, DRS
provides spectral information and thus enables differentiation between various chromophores. The accuracy and
robustness of the inverse analysis is thus considerably improved compared to use of either technique on its own.
Our analysis approach is simultaneous multi-dimensional fitting of the measured PPTR signals and DRS with
predictions from a numerical model of light-tissue interaction (a.k.a. inverse Monte Carlo). By using a three-layer skin
model (epidermis, dermis, and subcutis), we obtain a good match between the experimental and modeling data.
However, dividing the dermis into two separate layers (i.e., papillary and reticular dermis) helps to bring all assessed
parameter values within anatomically and physiologically plausible intervals.
Both the quality of the fit and the assessed parameter values depend somewhat on the assumed scattering properties for
skin, which vary in literature and likely depend on subject's age and gender, anatomical site, etc. In our preliminary
experience, simultaneous fitting of the scattering properties is possible and leads to considerable improvement of the fit.
The described approach may thus have a potential for simultaneous determination of absorption and scattering properties
of human skin in vivo.