Pulsed photothermal radiometry (PPTR) allows noninvasive determination of temperature depth profiles induced by
pulsed laser irradiation of strongly scattering biological tissues and organs, including human skin. In present study, we
evaluate the potential of this technique for investigational characterization and possibly quantitative evaluation of laser
The study involved 5 healthy volunteers (3 males, 2 females), age 20-30 years, undergoing tattoo removal treatment
using a Q-switched Nd:YAG laser. There were four measurement and treatment sessions in total, separated by 2-3
months. Prior to each treatment, PPTR measurements were performed on several tattoo sites and one nearby healthy site
in each patient, using a 5 ms Nd:YAG laser at low radiant exposure values and a dedicated radiometric setup. The laser-induced
temperature profiles were then reconstructed by applying a custom numerical code. In addition, each tatoo site
was documented with a digital camera and measured with a custom colorimetric system (in tristimulus color space),
providing an objective evaluation of the therapeutic efficacy to be correlated with our PPTR results.
The results show that the laser-induced temperature profile in untreated tattoos is invariably located at a subsurface depth
of 300 μm. In tattoo sites that responded well to laser therapy, a significant drop of the temperature peak was observed in
the profiles obtained from PPTR record. In several sites that appeared less responsive, as evidenced by colorimetric data,
a progressive shift of the temperature profile deeper into the dermis was observed over the course of consecutive laser
treatments, indicating that the laser tattoo removal was efficient.