Derpartment of Dermatology, Graduate School of Medicine, Osaka Metropolitan University, 1-4-3 Asahimachi, Abeno, Osaka, 545-8585, Japan.
Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka, 565-0871, Japan.
Sci Rep. 2024 Aug 29;14(1):20112. doi: 10.1038/s41598-024-70807-7.
Short-pulsed lasers can treat dermal pigmented lesions through selective photothermolysis. The irradiated light experiences multiple scattering by the skin and is absorbed by abnormal melanosomes as well as by normal blood vessels above the target. Because the fluence is extremely high, the absorbed light can cause thermal damage to the adjacent tissue components, leading to complications. To minimize radiant exposure and reduce the risk of burns, a model of the melanosome-disruption threshold fluence (MDTF) has been developed that accounts for the light-propagation efficiency in the skin. However, the light-propagation efficiency is attenuated because of multiple scattering, which limits the extent to which the radiant exposure required for treatment can be reduced. Here, this study demonstrates the principle of melanosome disruption with localized thermal damage through a turbid medium by ultralow radiant exposure of a short-pulsed laser. The MDTF model was combined with a wavefront-shaping technique to design an irradiation condition that can increase the light-propagation efficiency to the target. Under this irradiation condition, melanosomes were disrupted at a radiant exposure 25 times lower than the minimal value used in conventional laser treatments. Furthermore, almost no thermal damage to the skin was confirmed through a numerical simulation. These experimental and numerical results show the potential for noninvasive melanosome disruption and may lead to the improvement of the safety of short-pulsed laser treatment.
短脉冲激光可以通过选择性光热解来治疗皮肤色素病变。受激光在皮肤中经历多次散射，并被异常黑色素体以及目标上方的正常血管吸收。由于剂量极高，被吸收的光会对邻近组织成分造成热损伤，导致并发症。为了尽量减少辐射暴露并降低灼伤风险，已经开发出一种黑色素体破坏阈值剂量（MDTF）模型，该模型考虑了皮肤中的光传播效率。然而，由于多次散射，光传播效率会减弱，这限制了治疗所需的辐射暴露量可以降低的程度。在这里，通过超短脉冲激光的超低辐射暴露，通过混浊介质实现局部热损伤来证明黑色素体破坏的原理。将 MDTF 模型与波前整形技术相结合，设计了一种可以增加目标光传播效率的辐照条件。在这种辐照条件下，黑色素体在辐射暴露下被破坏，其辐射暴露值比传统激光治疗中使用的最小值低 25 倍。此外，通过数值模拟几乎可以确认对皮肤没有热损伤。这些实验和数值结果表明了非侵入性黑色素体破坏的潜力，可能会提高短脉冲激光治疗的安全性。
