A split tattoo comparative evaluation of sequential QS nanosecond laser followed by QS picosecond laser versus QS picosecond laser alone in tattoo removal: a prospective study

Laser tattoo removal was first reported by Goldman et al., and its mechanism is explained by the principles of selective photothermolysis and photoacoustics.According to photothermal theory, laser energy is selectively absorbed by pigment particles, and the optimal pulse duration should be less than or equal to the thermal relaxation time (TRT) of the chromophore. Photon absorption also generates pressure waves, which form the basis of inertial confinement time (ICT). When the laser pulse duration is shorter than the ICT, strong photoacoustic forces rupture the pigment particles. Thus, both theories emphasise the importance of selecting an appropriate wavelength and pulse width for effective and safe tattoo clearance.

Q-switched nanosecond (NS) lasers have long been considered the gold standard due to the selective photothermolysis of tattoo pigments. However, multiple sessions are usually required, with incomplete clearance and risk of pigmentary changes or scarring.

Picosecond (PS) lasers, which have emerged in recent years, are a strong competitor of NS lasers. They have demonstrated superior efficacy by delivering higher peak power with shorter pulse durations, resulting in more effective photomechanical pigment fragmentation and potentially fewer sessions.

Split-tattoo and intra-tattoo comparative trials have generally shown PSL to be superior or at least non-inferior to NSL for many pigments, but most published split studies compare each modality used alone (NSL vs PSL).

Although QS nanosecond lasers remain widely used, and the sequential use of NS followed by PS lasers has been proposed to maximise efficacy, combining the deeper penetration of NS pulses with the finer fragmentation of PS pulses. This sequential approach may enhance tattoo clearance while limiting side effects.