Follow-up visualization of in-vivo colored tattoo particles after picosecond laser treatment via multiphoton tomography

Picosecond (ps) lasers have emerged as a promising tool for effectively removing unwanted tattoos. However, data on the in vivo elimination process after ps laser treatment is limited. Multiphoton tomography (MPT) is an established intravital imaging technique and provides high-resolution subcellular visualization of the morphology of tattoos and the skin. The aim of this study is to visualize and characterize the distribution of tattoo particles after ps laser treatment using MPT-FLIM. Patients seeking a laser tattoo removal were recruited and received one to three 532/1064nm ps laser treatment sessions. MPT-FLIM measurements were scheduled six to eight weeks post-treatment. The number and size of tattoo granules decreased with subsequent treatments. Even months after the last ps laser treatment, tattoo pigments were still detectable in the upper epidermal layers and around vessels, indicating a continuous elimination process. Metabolic analysis by calculating the mean fluorescence lifetime (τm) revealed a persistent inflammatory status at follow-up visits. Our study concludes that MPT-FLIM is a suitable non-invasive technique for characterizing tattoo particles after ps laser treatment. Its clinical application enables monitoring and adjustment of treatment based on individual responses.