Are picosecond lasers as good as they claim?
Tattoos can be removed by either nanosecond or picosecond lasers. Nanosecond lasers have been used for this purpose since the early 1980s when my group first successfully demonstrated the scar-free clearance of black tattoo ink using a Q-switched ruby laser in Canniesburn Hospital, Glasgow. (Reid W.H., Miller I.D., Murphy M.J., Paul J.P., Evans J.H. “Q-switched Ruby Laser Removal of Tattoo : A 9-Year Review.” British Journal of Plastic Surgery, 1990, 43, 663-669. (LINK))
We calculated that the peak powers emitted by this laser were inducing a photoacoustic (or photomechanical) effect on the surfaces of the tattoo ink particles. Histology showed a minimal thermal effect in the tissues immediately surrounding those particles. However, clinical scarring was rare.
Picosecond lasers use shorter pulsewidths than nanosecond lasers – typically between 350 and 750 picosecond (or, 0.35 to 0.75 nanosecond, so they are only just sub-nanosecond!).
These result in higher peak powers which is the important parameter when inducing photoacoustic reactions. Consequently, the absorbed laser energy is more confined, in terms of time, than with nanosecond pulses. This, apparently, results in a ‘better’ overall effect with ‘faster’ clearances and ‘less pain’ – according to the laser suppliers.
However, some suppliers are claiming that their new picosecond lasers are better because they don’t induce the photothermal effects ‘that occur with nanosecond lasers.’
This, of course, is utter nonsense!!
Apart from the lack of histological evidence, there is no reason to assume that picosecond pulses will induce less thermal damage than nanosecond pulses. None!
The speed of delivery of the laser energy does not affect the thermal conduction following, or during, those pulses (on these timescales). To claim otherwise is just garbage! It’s a marketing claim with no scientific or clinical evidence to back it up.
Tattoo colours and wavelengths
Another claim I constantly hear is that picosecond lasers can clear “all colours”. This is also nonsense. The absorption of laser energy by any tattoo ink is determined buy its absorption coefficient – in other words, the colour and the wavelength have to ‘match’ to a certain degree. If the match is poor (low coefficient) then there will be minimal absorption by the ink. The fact that the laser pulse is a picosecond pulse makes little to no difference (unless you want to consider two-photon absorption or non-linear processes, of course!!)
The only way to guarantee this claim is to provide as many wavelengths as possible in a laser. I think there is one manufacturer now providing three wavelengths in a picosecond system. This will certainly be better than a two-wavelength system, but it is still not capable of clearing “all colours”!
So, are they better?
As to whether picosecond lasers actually speed up the whole tattoo removal process, a review was carried out by Reiter et.al. in 2016. (Picosecond lasers for tattoo removal: a systematic review, Reiter O., et al., Lasers Med Sci, 2016, 31: 1397, dos:10.1007/S10103-016-2001-0).
Their conclusion was “There is sparse evidence that picosecond lasers are more effective than their nanosecond counterparts for mainly black and blue ink tattoo removal, with minor side effects.”
Interesting! Personally, I’ve always thought that the improvement in results due to using a picosecond pulse is not worth the huge increase in price (compared with nanosecond systems).
So, if you decide to buy a picosecond laser make sure you do plenty of research first. Ask to see plenty of good, real clinical photographs – both good results and bad. These lasers are horrifically expensive and I’m not sure they are worth it!