低温喷雾冷却的动态行为：喷射持续时间和喷雾距离的影响。

Aguilar Guillermo, Wang Guo-Xiang, Nelson J Stuart

Department of Biomedical Engineering, University of California, Irvine, California 92697, USA.

Lasers Surg Med. 2003;32(2):152-9. doi: 10.1002/lsm.10133.

BACKGROUND AND OBJECTIVES

Cryogen spray cooling (CSC) is used to minimize the risk of epidermal damage during laser dermatologic surgery. Since optimization of CSC permits the safe use of higher light doses, which improves therapeutic outcome in many patients with superficial skin lesions, studies have focused on understanding spray-surface interactions and cooling dynamics. The objective of this study is to measure accurately temperature variations at the sprayed surface and the effects of spurt duration (deltat) and nozzle-to-sprayed surface distance (L) on cooling dynamics during CSC.

STUDY DESIGN/MATERIALS AND METHODS: A fast-response temperature measurement sensor is built using thin (20 microm) aluminum foil placed on top of a poly methyl-methacrylate resin (Plexiglass) with a 50 microm bead diameter thermocouple positioned in between. Liquid film residence time (t(r)) and minimum surface temperature (T(min)) are systematically measured as a function of deltat and L.

RESULTS

Two distinct spray-surface interaction mechanisms are recognized. The transition between them occurs at a critical length L(c) approximately 25-30 mm. Noticeable characteristics include: (1) for spurts at L < L(c), shorter t(r), and lower T(min) are reached as compared to L > L(c), T(min) is dependent on deltat and L, while t(r) is a function of deltat only; (2) for spurts at L > L(c), T(min) still depends on L but not on deltat, while t(r) becomes a function of both deltat and L. Finally, for all deltat, t(r) reaches a maximum at L = 40 mm.

CONCLUSIONS

Based on our results, a good choice to achieve low T(min) and t(r) for the treatment of superficial skin lesions may be met by using deltat of approximately 30-50 milliseconds and the shortest spray distance that is tolerable by the patient. Spurt durations (deltat) of more than 30-50 milliseconds at spray distances (L) greater than L(c) lead to higher T(min) and longer t(r). These parameters may be appropriate for laser therapy of deeper targets.

背景与目的

冷冻喷雾冷却（CSC）用于在激光皮肤外科手术中降低表皮损伤风险。由于优化CSC可安全使用更高的光剂量，这能改善许多浅表皮肤病变患者的治疗效果，因此研究集中在理解喷雾与表面的相互作用以及冷却动力学。本研究的目的是准确测量喷雾表面的温度变化以及喷射持续时间（δt）和喷嘴到喷雾表面距离（L）对CSC冷却动力学的影响。

研究设计/材料与方法：使用置于聚甲基丙烯酸甲酯树脂（有机玻璃）顶部的薄（20微米）铝箔构建一个快速响应温度测量传感器，在其间放置一个珠直径为50微米的热电偶。系统测量液膜停留时间（t(r)）和最低表面温度（T(min)）作为δt和L的函数。

结果

识别出两种不同的喷雾与表面相互作用机制。它们之间的转变发生在临界长度L(c)约25 - 30毫米处。显著特征包括：（1）对于L < L(c)的喷射，与L > L(c)相比，达到的t(r)更短，T(min)更低，T(min)取决于δt和L，而t(r)仅是δt的函数；（2）对于L > L(c)的喷射，T(min)仍取决于L但不取决于δt，而t(r)成为δt和L两者的函数。最后，对于所有δt，t(r)在L = 40毫米处达到最大值。

结论

基于我们的结果，对于浅表皮肤病变的治疗，要实现低T(min)和t(r)，一个好的选择可能是使用约30 - 50毫秒的δt以及患者可耐受的最短喷雾距离。在喷雾距离（L）大于L(c)时，喷射持续时间（δt）超过30 - 50毫秒会导致更高的T(min)和更长的t(r)。这些参数可能适用于更深层靶点的激光治疗。