We have recently introduced a novel methodology for noninvasive assessment of structure and composition of human skin in vivo1. The approach combines pulsed photothermal radiometry, involving time-resolved measurements of midinfrared emission after irradiation with a millisecond light pulse, and diffuse reflectance spectroscopy in visible part of the spectrum (400–600 nm). The experimental data are fitted simultaneously with respective predictions from a fourlayer Monte Carlo model of light transport in human skin. The described approach allows assessment of the contents of specific chromophores (melanin, oxy-, and deoxy-hemoglobin), as well as scattering properties and thicknesses of the epidermis and dermis. In present study we evaluate the potential of this approach for quantitative evaluation of tattoos. For this purpose, we apply a three-layer optical model of skin consisting of epidermis, upper dermis, and bottom dermis which includes the tattoo ink. The study involves healthy volunteer with black tattoo undergoing tattoo removal treatment with Q-switched Nd:YAG laser. The measurements are performed in four tattoo sites and one nearby healthy site before and after laser removal treatment. The results indicate the depth of tattoo, amount of tattoo ink and scattering properties in the dermis. This information can be used to improve our understanding of laser tattoo removal procedure.
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