Comparison of responses of tattoos to picosecond and nanosecond Q- switched neodymium:YAG lasers

Objective: To test the hypothesis that picosecond laser pulses are more effective than nanosecond domain pulses in clearing of tattoos. Design: Intratattoo comparison trial of 2 laser treatment modalities. Setting: A large interdisciplinary biomedical laser laboratory on the campus of a tertiary medical center. Patients: Consecutive patients with black tattoos were enrolled; all 16 patients completed the study. Intervention: We treated designated parts of the same tattoo with 35-picosecond and 10-nanosecond pulses from 2 neodymium:YAG lasers. Patients received a total of 4 treatments at 4-week intervals. All laser pulse parameters were held constant except pulse duration. Radiation exposure was 0.65 J/cm² at the skin surface. Biopsies were performed for routine microscopic and electron microscopic analysis at the initial treatment session and 4 weeks after the final treatment in 8 consenting patients. Also, ink samples were irradiated in vitro. Main Outcome Measures: In vivo, on the completion of treatment, a panel of dermatologists not associated with the study (and blinded to the treatment type) evaluated photographs to assess tattoo lightening. Formalin- fixed specimens were examined for qualitative epidermal and dermal changes as well as depth of pigment alteration. Electron micrographs were examined for particle electron density and size changes (in vivo and in vitro). The gross in vitro optical density changes were measured. Results: In 12 of 16 tattoos, there was significant lightening in the picosecond-treated areas compared with those treated with nanosecond pulses. Mean depth of pigment alteration was greater for picosecond pulses, but the difference was not significant. In vivo biopsy specimens showed similar electron-lucent changes for both pulse durations. In vitro results were similar for both pulse durations, showing increases in particle sizes and decreased electron density as well as gross ink lightening. Conclusions: Picosecond pulses are more efficient than nanosecond pulses in clearing black tattoos. Black tattoos clear principally by laser-induced changes in the intrinsic optical properties of the ink.