Background and Objective:
In dermatologic laser therapy, cryogen spray cooling (CSC) is a means to protect the epidermis while leaving dermal structures susceptible to thermal damage. The purpose of this study was to determine optimal spurt duration, s , and optimal delay, d , between the cryogen spurt and laser pulse when using CSC in treatment of port wine stain birthmarks.
Study Design/Materials and Methods
: A finite difference method is used to compute temperature distributions in human skin in response to CSC. Optimal s and d are determined by maximizing the temperature difference between a modeled basal layer and an imaginary target chromophore. Results: The model predicts an optimal s of 170-300 msec and approximately 400 msec for shallow (150 m) and deeper (400 m) targets, respectively. Spraying for longer than the optimal s does not critically impair cooling selectivity. For a spurt duration of 100 msec, optimal delays are 5-10 msec and 25-70 msec for a shallow and deep basal layer, respectively. Conclusion: In the absence of knowledge about the lesion anatomy, using a s of 100-200 msec and no delay is a good compromise. A delay is justified only when basal layer and target chromophore are relatively deep and the optimal spurt duration cannot be applied, e.g., to avoid frostbite. Lasers Surg. Med. 27:165-170, 2000