Hohman Marc H., Ramsey Michael L.
Uniformed Services University/Madigan Army Medical Center
Geisinger Health System
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 . 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 (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.
自史前时代起，纹身就已应用于人类皮肤，用于作为通过仪式、群体成员标志、美容提升、创伤后遗症、医疗程序的组成部分，甚至作为惩罚手段。据推测，去除纹身的愿望也同样由来已久。早期的纹身去除方法包括冷冻疗法、手术切除以及皮肤表面修复技术，如磨皮或化学剥脱。冷冻疗法和切除纹身皮肤往往会留下残留的质地变化或手术疤痕，对于大面积纹身可能并不适用。另一方面，皮肤表面修复仅作用于乳头层真皮，这对于去除业余纹身可能有效，但不太可能影响更深层的专业纹身。1960年，休斯研究实验室制造出了第一台通过受激辐射实现光放大的装置（激光），并使用合成红宝石作为激光介质；1965年，首次报道了使用红宝石作为激光介质的用于纹身去除的激光。激光相较于其他纹身去除方式的优势在于，激光能够特异性地靶向纹身中的色素，从而将对周围皮肤的损伤降至最低，进而降低留疤和色素沉着异常的风险，同时保持或提高疗效。由于激光在定义上是准直、相干且单色的，激光产生的每种波长的光将主要被特定的目标发色团分子吸收，从而产生……因此，成功去除纹身的关键在于根据纹身颜色和周围皮肤颜色选择合适的激光波长，并确保能量脉冲以能将对周围组织的热损伤降至最低的方式传递。早期的激光发出的能量脉冲持续时间在毫秒范围内，这会导致发色团周围的组织过热并受损，引发更多炎症、疤痕形成以及对黑素细胞的损伤，进而导致后续色素减退或色素沉着。当脉冲持续时间超过组织的热弛豫时间（即组织从激光脉冲获得的热量散失50%所需的时间）时，这些不良事件更有可能发生。对于纹身颗粒而言，这个时间可能短至10纳秒，这就需要非常短的激光脉冲以避免超过热弛豫时间。解决方案来自所谓的调Q（QS或Q开关）激光，其产生的脉冲宽度在纳秒范围内。这些激光已成为纹身去除的主要手段，因为它们能够去除或淡化多种颜色的色素，同时降低治疗后烧伤、疤痕以及色素减退或色素沉着的发生率。最近，进一步的技术进步导致了皮秒激光的发展，这种激光能够以如此短的脉冲传递能量，以至于在第一批光子到达皮肤之前激光束发射就已开始并结束。
