Comparison of picosecond versus nanosecond Nd:YAG lasers for the removal of cosmetic tattoos in an animal model.

Cosmetic tattoos are difficult to remove, and their response to picosecond laser treatment has seldom been investigated. We compared the efficacy and adverse effects of picosecond versus Q-switched lasers for the removal of cosmetic tattoos. White, flesh-colored, and brown inks were irradiated using 532/1064 nm picosecond and Q-switched Nd:YAG lasers, and their absorption spectra before and after laser irradiation were analyzed. Nine rats were tattooed with all three inks. Each tattoo was divided into three sections and treated at 1064 nm with a picosecond laser or Q-switched laser, or left untreated, in four sessions at 1-month intervals. Skin biopsies were taken from treated and untreated sites. In vitro study showed the 1064 nm picosecond laser caused the least paradoxical color shift. In vivo study showed that all white tattoos achieved poor response scores, six flesh-colored tattoos achieved fair to good response scores, and seven brown tattoos achieved good to excellent response scores with the picosecond laser. The picosecond laser was superior to the Q-switched laser for removing flesh-colored tattoos (P < 0.05), but the effectiveness for white and brown tattoos was similar for both lasers. The degree of paradoxical darkening when removing the white and flesh-colored tattoos was significantly lower with the picosecond than that with the Q-switched laser (P < 0.01). Transmission electron microscopy showed that many tattoo ink particles had decreased in size after irradiations with both pulse durations. The 1064 nm picosecond Nd:YAG laser causes mild paradoxical darkening and might be more appropriate for removal of flesh-colored and brown cosmetic tattoos.