Our group has recently presented a novel technique for noninvasive assessment of the structure and composition of human skin in vivo. The approach combines two optical techniques, photothermal radiometry and diffuse reflectance spectroscopy in visible part of the spectrum with numerical modeling of light transport in a four-level model of human skin, and enables assessment of the contents of specific chromophores (e.g., melanin, oxy-, and deoxy-hemoglobin), as well as scattering properties and thicknesses of the epidermis and dermis. In this study, we try to quantitatively validate the described approach by analyzing a series of optically homogeneous skin phantoms with varying concentrations of absorbing dye (Congo red) and optical scatterers. Twelve such phantoms were made from bovine collagen gel and their scattering properties were controlled by adding TiO2 nanoparticles with diameters of 200nm and 490nm, aiming at the range of values typical of human dermis. The applied Monte Carlo model of light transport takes into account the actual diameter and thickness of the phantoms and allows simultaneous assessment of the absorption coefficient as well as the amplitude and spectral power of the reduced scattering coefficient. The obtained values are proportional to the respective concentrations of the absorbing dye and scatterers, but don’t match the theoretical predictions (from a Mie simulator).
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