摘要
太田痣激光热疗的原理是用激光能量崩解真皮增生的黑色素,但表皮正常黑色素同样吸收激光能量,需要对其进行预冷却以避免热损伤。已经成功应用于辅助治疗葡萄酒色斑的瞬态制冷剂喷雾冷却很有潜力,但需进一步提高冷却能力并缩短液膜残留时间以避免对激光能量的衰减和皮肤感染。具有低沸点、高潜热、低全球变暖潜能值的R-32制冷剂有望成为R-134a和R-404A制冷剂的替代品。搭建了制冷剂瞬态喷雾冷却与激光能量衰减测试系统对喷雾冷却性能开展了实验研究。R-32制冷剂喷雾冷却下的热流密度峰值最大(519.0kW·m^(-2))且液膜残留时间最短(142 ms),对755nm和1064nm的激光能量衰减最小。在喷雾开始63 ms后,R-32制冷剂喷雾对1064nm激光的能量衰减小于6%。R-32制冷剂喷雾的冷却能力强,液膜残留时间短,对激光衰减小且对环境友好,表明R-32制冷剂具有较好的临床应用潜能。
Objective In laser surgery of Ota’s nevus,the hyperplastic melanin particles in dermis explosively break up under high-power laser irradiation.However,laser energy can also be absorbed by normal melanin in epidermis,which necessitates pre-cooling to prevent the thermal damage of epidermis.Cryogen spray cooling(CSC)with short spurt duration(<100 ms)using R-134a and R-404A cryogens has a high clinical potential to assist laser surgery of Ota’s nevus,which has been successfully used in the laser treatment of port-wine stain(PWS)birthmarks.But the blindingly high global warming potential(GWP)value(1430 for R-134a,and 3850 for R-404A)necessitates the substitution of a new cryogen.Also,the cooling capacity is needed to enhance,and the residence time of liquid films should be shortened to avoid laser attenuation and skin infection during laser surgery of Ota’s nevus.R-32 cryogen with a low boiling point,high latent heat and a low GWP is a possible substitution of R-134a and R-404A.Nevertheless,the cooling performance and light absorption during R-32 spray,as well as the complicated interaction mechanism between spray and lasers remain unknown.The investigation on the cooling performance and light attenuation dynamics is urgent to evaluate the clinical potential of R-32,and provides precise theoretical guidance for cooling parameter optimization in clinics.Methods A transient CSC facility is constructed to evaluate the cooling performance and laser energy attenuation induced by R-134a,R-404A,and R-32 sprays.To avoid the spatial interference between spray and the vertically irradiated laser,the cryogen is spurted obliquely on the surface with an inclined angle of 60°,which is similar to that of clinical-used Vbeam^(TM)laser equipped with a dynamic cooling device(DCD).The spray distance and spurt duration are set as 30 mm and 50 ms by a three-dimensional translational electric positioner and a fast response solenoid valve.A thin-film type-T thermocouple(TFTC)deposited on the epoxy resin is employed to measure surface temperature.After obtaining the temperature variation,the surface heat flux is computed using the Duhamel theorem.The agar skin phantom with similar absorption and scattering properties of human skin is elaborately prepared to measure the dynamic laser energy attenuation under the clinical-used 755-nm and 1064-nm laser irradiation.The transmitted laser energy is collected by the integrating sphere connected with a pre-calibrated silicon photodiode.The light transmittance is calculated by the ratio of laser energy measurements taken before and after CSC.The liquid film deposition and frost formation on the skin phantom surface are recorded by a high-speed camera using the scattering illumination method.The control and data collection are implemented by the national instruments data acquisition(NI-DAQ)board and the self-code LabVIEW program.Results and Discussions The cooling performance highly depends on cryogens.The minimum surface temperatures reach-46.1,-57.9 and-63.7℃,and the maximum surface heat flux values are 294.9,377.4 and 519.0 kW/m(2)for R-134a,R-404A and R-32,respectively(Figs.3 and 4).The maximum surface heat flux of R-32 increases by 79.5%and 37.5%,as compared with those of R-134a and R-404A.The similarity in dimensionless surface heat flux values for R-134a,R-404A,R-407C and R-32 is observed based on the dimensionless analysis(Fig.5).A general transient surface heat flux correlation for four cryogens is proposed by correlating spray Biot number(Bi^(*))and Fourier number(F_(os)).Transient cooling can be divided into two stages,namely,fast boiling cooling(F_(os)/F_(os.max)<1)and film evaporation cooling(F_(os)/F_(os.max)>1).Three distinct stages,namely,the scattering by droplet(t≤86 ms),liquid film absorption(86 ms<t≤448 ms),and scattering by frost(t>448 ms)are observed during and after CSC(Fig.6).Most of the laser energy is attenuated in the stage of frost formation.For three cryogens,the laser attenuation is the least under R-32 spray cooling because of the fast evaporation of liquid films(Fig.7).When t>63 ms,light attenuation is less than 6%during R-32 spray cooling under 1064-nm laser irradiation(Fig.8).Conclusions R-32 with a low boiling point,high latent heat and a low GWP is promising to resplace R-134a and R-404A with high GWPs.Whereas the clinical potential in terms of cooling performance and laser attenuation is needed to be evaluated,and the complicated interaction mechanism between spray and lasers is urgent to be understood to optimize cooling parameters for clinicians.In this paper,the cooling performance and laser attenuation for R-134a,R-404A and R-32 are compared using the well-constructed transient CSC facility.Results demonstrate that three distinct stages of scattering by droplet,liquid film absorption and scattering by frost occurs in the variation of light transmittance.R-32 has the maximum surface heat flux(519.0 kW·m^(-2)),the shortest liquid film residence time(142 ms),and the least light attenuation under the irradiations of 755-nm and 1064-nm lasers owing to the low boiling point and large latent heat.The strong cooling capability,short liquid film residence time and small light attenuation of environment-friendly R-32 imply its good clinical application potential.But the clinical safety and feasibility of R-32 still requires the validation of clinical trials in patients,because of the absence of medical cryogens.
作者
田加猛
陈斌
周致富
李东
Tian Jiameng;Chen Bin;Zhou Zhifu;Li Dong(School of Energy and Power Eyigineering,Jiangsu University,Zhenjiang,Jiangsu 212013,China;State Key Laboratory of Multiphase Flow in Power Engineering,Xi'an Jiaotong University,Xi'an,Shaanxi 710049,China)
出处
《中国激光》
EI
CAS
CSCD
北大核心
2022年第5期56-65,共10页
Chinese Journal of Lasers
基金
国家自然科学基金(52036007,52106201)
江苏省自然科学基金(BK20210763)。
关键词
医用光学
瞬态喷雾冷却
太田痣激光手术
R-32
冷却性能
激光能量衰减
medical optics
transient spray cooling
laser treatment of Ota’s nevus
R-32
cooling performance
laser energy attenuation
