Objective noninvasive monitoring of laser tattoo removal in a human volunteer: a proof of principle study

Abstract

We explore the potential for noninvasive monitoring of laser tattoo removal treatment by adapting a recently introduced methodology for quantitative assessment of structure and composition of human skin in vivo.1 The approach combines diffuse reflectance spectroscopy in visible part of the spectrum with pulsed photothermal radiometry, involving timeresolved measurements of mid-infrared emission after irradiation with a millisecond laser pulse. The experimental data are fitted simultaneously with the respective predictions of a dedicated numerical model of light and heat transport in tattooed skin. For this purpose we apply a three-layer optical model of skin, consisting of epidermis, upper dermis, and lower dermis which includes the tattoo ink. This proof of principle study involved one healthy volunteer undergoing tattoo removal treatment. One half of the tattoo was treated with 5 ns pulses from a commercial Nd:YAG laser (StarWalker® MaQX, Fotona) at radiant exposure of 3 J/cm2, and the other half with much shorter, "picosecond" pulses at the same wavelength and 1.3 J/cm2. Measurements were performed before and 8 weeks after the first treatment session, as well as 20 weeks after the second treatment. The results show a significant reduction of the ink content and an increase of the subsurface depth of the tattoo layer over the course of treatment with both lasers, in agreement with gradual fading of the tattoo.