Laser Tattoo Removal

Excerpt

Tattoos have been applied to human skin since prehistory as rights of passage, indications of group membership, aesthetic enhancements, sequelae of trauma, components of medical procedures, and even as penalties. Presumably, the desire to remove them has existed for just as long. Early tattoo removal methods included cryotherapy, surgical excision, and skin resurfacing techniques, such as dermabrasion or chemical peeling. Cryotherapy and resection of the tattooed skin tend to leave residual textural changes or surgical scars and may not be feasible for large tattoos. On the other hand, skin resurfacing only reaches down to the papillary dermis, which may be effective for removing amateur tattoos but is unlikely to affect deeper, professional tattoos.

The first device that produced light amplificated by the stimulated emission of radiation (laser) was built at Hughes Research Laboratories in 1960 and used a synthetic ruby as a lasing medium; the first report of a laser used for tattoo removal followed in 1965, using ruby as the lasing medium as well. The advantage of lasers over other modalities of tattoo removal is that lasers can target the pigment in tattoos specifically and thereby minimize damage to the surrounding skin, thus lowering the risk of scarring and dyspigmentation while preserving or enhancing efficacy. Because laser light is, by definition, collimated, coherent, and monochromatic, each wavelength of light produced by a laser will be absorbed primarily by specific target chromophore molecules, resulting in selective photothermolysis.

The keys to successful tattoo removal, therefore, are the selection of the appropriate laser wavelength in the context of the color of the tattoo and the surrounding skin and ensuring that the energy pulses are delivered in such a way as to minimize thermal injury to the surrounding tissue. Early lasers delivered energy pulses with durations in the millisecond range, which had the effect of overheating and damaging the tissue surrounding the chromophore, leading to more inflammation, scarring, and injury to melanocytes that caused subsequent hypo- or hyperpigmentation. These adverse events are more likely to occur when the pulse duration exceeds the thermal relaxation time of the tissue—the time it takes for the tissue to lose 50% of the heat it gains from the laser pulse.

This time may be as brief as 10 ns for tattoo particles, necessitating a very short laser pulse to avoid exceeding the thermal relaxation time. The solution came from so-called quality-switched (QS or Q-switched) lasers, which produce pulse widths in the nanosecond range. These lasers have become a mainstay of tattoo removal because of their ability to remove or lighten pigments of multiple colors while decreasing the incidence of post-treatment burns, scars, and hypo- or hyperpigmentation. Further technological advancements have more recently resulted in the development of picosecond lasers, which can deliver energy in such short pulses that laser beam emission begins and ends before the first photons reach the skin.