Svaasand Lars O, Nelson J Stuart
Norwegian University of Science and Technology, NO-7491 Trondheim, Norway.
J Biomed Opt. 2004 Mar-Apr;9(2):353-61. doi: 10.1117/1.1646174.
The physical basis for optimization of wavelength, pulse duration, and cooling for laser-induced selective photothermolysis of hair follicles in human skin is discussed. The results indicate that the most important optimization parameter is the cooling efficiency of the technique utilized for epidermal protection. The optical penetration is approximately the same for lasers at 694, 755, and 800 nm. The penetration of radiation from Nd:yttrium-aluminum-garnet lasers at 1064 nm is, however, somewhat larger. Photothermal damage to the follicle is shown to be almost independent of laser pulse duration up to 100 ms. The results reveal that epidermal cooling by a 30-80-ms-long cryogen spurt immediately before laser exposure is the only efficient technique for laser pulse durations less than 10 ms. For longer pulse durations in the 30-100 ms range, protection can be done efficiently by skin cooling during laser exposure. For laser pulses of 100 ms, an extended precooling period, e.g., by bringing a cold object into good thermal contact with the skin for about 1 s, can be of value. Thermal quenching of laser induced epidermal temperature rise after pulsed exposure can most efficiently be done with a 20 ms cryogen spurt applied immediately after irradiation.
本文讨论了优化波长、脉冲持续时间和冷却方式，以实现对人体皮肤毛囊进行激光诱导选择性光热解的物理基础。结果表明，最重要的优化参数是用于表皮保护的技术的冷却效率。对于波长为694、755和800 nm的激光，其光学穿透深度大致相同。然而，波长为1064 nm的掺钕钇铝石榴石激光的辐射穿透深度则稍大一些。研究表明，在激光脉冲持续时间长达100 ms时，对毛囊的光热损伤几乎与脉冲持续时间无关。结果显示，对于激光脉冲持续时间小于10 ms的情况，在激光照射前立即进行30 - 80 ms的制冷剂喷射进行表皮冷却是唯一有效的技术。对于30 - 100 ms范围内的较长脉冲持续时间，在激光照射期间通过皮肤冷却可以有效地实现保护。对于100 ms的激光脉冲，延长预冷却时间，例如通过将一个冷物体与皮肤良好地热接触约1 s，可能会有帮助。在脉冲照射后，通过在照射后立即进行20 ms的制冷剂喷射，可以最有效地实现对激光诱导的表皮温度升高的热猝灭。
