Picosecond Laser Treatment for Tattoos and Benign Cutaneous Pigmented Lesions (Secondary publication)

Abstract

Background and aims: The selective removal of tattoos and benign cutaneous pigmented lesions with laser energy evolved rapidly with the development of the nanosecond-domain Q-switched laser (ns-laser). Recently, however, a series of picosecond-domain lasers (ps-lasers) with pulsewidths less than 1 ns has become commercially available, enabling more efficient and faster removal of pigmented lesions in the field of dermatologic laser surgery.

Rationale behind the ps-laser: The efficacy of the ns-laser depended on the theory of selective photothermolysis, whereby an extremely short pulse width was delivered less than the thermal relaxation time (TRT) of a target. At sub-ns pulsewidths, i.e. in the ps-domain, this efficacy is dramatically extended through defeating the stress relaxation time (SRT) of a target allowing for even more effective pigment destruction with even less damage to the surrounding normal tissue. This will be discussed in detail.

Clinical applications: The ps-laser has been reported as achieving tattoo removal in fewer sessions than the ns-laser, with less in the way of unwanted side effects. Tattoos recalcitrant to ns-laser treatment have responded well to the ps-laser, and although true 'color blindness' is not yet completely achieved with the ps-domain pulses currently available, multicolored tattoos have also responded very favorably. The ability to limit damage precisely to the pigment target gives greater efficacy in treatment of epidermal lesions with less induction of post-inflammatory hyperpigmentation in the PIH-susceptible Asian skin, and dermal melanocytosis also respond very well to ps-laser treatment. Illustrative clinical examples from the author's experience are given.

Conclusions: Current ps-lasers could be a revolutionary advance for laser tattoo removal but may be less effective for some specific aesthetic indications such as melasma and other cosmetic procedures. Manufacturers must make an effort to reduce the current comparatively long ps-domain pulsewidths to deliver a 'true' ps-domain laser, with more basic studies also being required to allow expansion of the safe and effective use of the ps-laser outside of tattoo removal.

Keywords: Q-switched laser; photoacoustic reaction; photothermal reaction; picosecond laser; tattoo.

Fig. 1

Mechanism of thermal lock-in. (Reproduced with permission from reference #14) (a) Thermal diffusion: Thermal infusion with a long period of time results in thermal diffusion. (b) Thermal lock-in: Thermal infusion within a short time results in thermal lock-in causing rise in temperature and vaporization of particle.

Fig. 2

Mechanism of stress lock-in. ( Reproduced with permission from reference #14). (a) Stress diffusion: Mechanical stress generated with a long period of time results in stress (vibration) diffusion. (b) Stress lock-in: Mechanical stress generated within a very short period of time results in stress lock-in causing rise in pressure and fracture of the particle.

Fig. 3

Case 1, tattoo on the forearm. (a) Before treatment, (b) Two months after 4 times treatment by Pico-Alex. (For interpretation of the references to color in this figure legend, the reader is refered to the web version of this article.)

Fig. 4

Case 2, tattoo on the back. (a) Before treatment, (b) Two months after 1 time QSYL treatment and 5 times Pico-Alex treatment. (For interpretation of the references to color in this figure legend, the reader is refered to the web version of this article.)

Fig. 5

Case 3, tattoo on the chest. (a) Before treatment, (b) Two months after 1 time Pico -Alex treatment. (For interpretation of the references to color in this figure legend, the reader is refered to the web version of this article.)

Fig. 6

Case 4, tattoo on the upper arm. (a) Before treatment, (b) After 3 times treatment by Pico-Alex, (c) After 5 times treatment by Pico-Alex, (d) One month after five Pico-Alex plus one Pico-YAG (532) treatment. (For interpretation of the references to color in this figure legend, the reader is refered to the web version of this article.)

Fig. 7

Case 5, Nevus of Ota on the left cheek. (a) Before treatment, (b) Four months after one treatment by Pico-Alex. (For interpretation of the references to color in this figure legend, the reader is refered to the web version of this article.)

Fig. 8

Case 6, ectopic mongolian spot on the chest and upper extremity. (a) Before treatment, (b) Four months after one treatment by Pico- Alex (chest) and QSRL (arm). (For interpretation of the references to color in this figure legend, the reader is refered to the web version of this article.)

Fig. 9

Case 7, solar lentigo on the right cheek. (a) Before treatment, (b) Immediately after treatment, the lesion shows immediate whitening phenomenon. (c) Ten days after treatment, the pigment of the lesion was removed. (d) One months after treatment, the lesion keeps white with subtle marginal hyperpigmentation. (For interpretation of the references to color in this figure legend, the reader is refered to the web version of this article.)

Fig. 10

Case 8, disseminated solar lentigines on the face. (a) Before treatment, (b) One months after 2 times treatment using Pico-Alex with middle fluence at pigment spot and with low fluence on the whole face. (For interpretation of the references to color in this figure legend, the reader is refered to the web version of this article.)