Objective: To evaluate the therapeutic effect of a novel air-cooled Nd:YAG laser in the venous lakes of the lips (VLL). Background: The thermal injury is one of the most important issues during laser therapy for venous lakes. Methods: Six pieces of fresh pork livers were used to provide 30 regions with a diameter of 6 mm for experiment in vitro, among which 15 regions were treated by Nd:YAG laser with air cooling until the tissue turned gray-white, whereas the rest were treated without air cooling as control. The operation time of laser irradiation, the degree of temperature increase, and the depth of coagulation tissue were compared between two groups. Then, 60 VLL patients were selected for Nd:YAG laser treatment with or without air cooling. The operation time of laser irradiation, the degree of temperature increase, the postoperative pain visual analog scale (VAS) score, and the percentage of lesions removed within 1 month were compared. Results: In tissue studies, the treated group showed a longer operation time of laser irradiation (p < 0.01), a lower degree of temperature increase (p < 0.01), and there was no significant statistical difference in the depth of coagulation tissue (p = 0.624). In clinical studies, the treated group showed a longer operation time of laser irradiation (p < 0.01), a lower degree of temperature increase (p < 0.01), and a lower VAS score on the 1st and 2nd day, compared with the control group (p < 0.01). Conclusions: Air cooling during Nd:YAG laser for the treatment of VLL can prolong the surgical time, but lowered tissue temperature and reduced patient pain within 2 days under the premise of ensuring the treatment effect.

Aiming to the personalized laser therapy of nevus of Ota (NO), a local thermal non-equilibrium model was employed to optimize laser wavelength, pulse duration, and energy density under different melanin depth and volume fraction. According to our simulation, the optimal pulse duration is between 15 and 150 ns to limit heat transfer inside the hyperplastic melanin, and 50 ns is recommended to decrease the energy absorption by normal melanin in epidermis. Correlations of the minimum and the maximum energy densities are proposed with respect to melanin depth and volume fraction for the 755-nm and 1064-nm lasers. For the same NO type, the therapy window of the 755-nm laser is larger than that of 1064-nm. For NO with shallow depth or low volume fraction, the 755-nm laser is recommended to make the treatment more stable owing to its lager therapy window. For deeper depth or higher volume fraction, the 1064-nm laser is recommended to avoid thermal damage of epidermis. Through comparison with clinical data, the optimized laser parameters are proved practicable since high cure rate can be achieved when energy density falls into the range of predicted therapy window. With developing of non-invasive measurement technology of melanin content and distribution, personalized treatment of NO maybe possible in the near future.

Based on the well-known principle of selective photothermolysis, laser has been a promising way for the treatment of port wine stains (PWSs). The laser wavelengths used for PWS\'s clinical treatment include but are not limited to pulsed dye laser (PDL) in 585-600 nm, long-pulse 755-nm alexandrite, and 1064-nm Nd:YAG lasers. The objective of this study was to investigate the optimal wavelength for PWS\'s laser treatment. A two-scale mathematic model was constructed to simultaneously quantify macroscale laser energy attenuation in two-layered bulk skin and microscale local energy absorption on target blood vessels within Krogh unit. The effects of morphological parameters, including epidermal melanin content, epidermal thickness, dermal blood content, blood vessel depth, and diameter on laser energy deposition within target blood vessels, were investigated from the visible to near-infrared bands (500-1100 nm). The energy deposition ratio of target blood vessel to epidermal surface was proposed to determine the optimal laser wavelength for PWS with different skin morphological parameters. The bioheat transfer modeling and animal experiment are also conducted to prove our wavelength optimization. The optimal wavelengths for lightly pigmented skin with small and shallow target blood vessels are 580-610 nm in the visible band. This wavelength coincides with commercially used PDL. The optimal wavelength shifts to 940 nm as the epidermal pigmentation increases or the size and blood vessel depth increases. The optimal wavelength changes to 1005 nm as the epidermal pigmentation or the size and burying depth of target blood vessel further increases. Nine hundred forty nanometers can be selected as a general wavelength in PWS treatment to meet the need in most widely morphological structure. Lasers with wavelengths in the 580-610, 940, and 1005 nm regions are effective for treating PWS because of their high optical selectivity in blood over the epidermis.