title: Optimal cryogen spray cooling parameters for pulsed laser treatment of port wine stains.
abstract: 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, tau(s), and optimal delay, tau(d), between the cryogen spurt and laser pulse when using CSC in treatment of port wine stain birthmarks.
  
  
  METHODS
  A finite difference method is used to compute temperature distributions in human skin in response to CSC. Optimal tau(s) and tau(d) are determined by maximizing the temperature difference between a modeled basal layer and an imaginary target chromophore.
  
  
  RESULTS
  The model predicts an optimal tau(s) of 170-300 msec and approximately 400 msec for shallow (150 microm) and deeper (400 microm) targets, respectively. Spraying for longer than the optimal tau(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.
  
  
  CONCLUSIONS
  In the absence of knowledge about the lesion anatomy, using a tau(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.
authors.affiliation: Beckman Laser Institute and Medical Clinic, University of California, Irvine, California, USA. wverkru@bli.uci.edu
authors.forename: W
authors.initials: W
authors.lastname: Verkruysse
authors.forename: B
authors.initials: B
authors.lastname: Majaron
authors.forename: B S
authors.initials: BS
authors.lastname: Tanenbaum
authors.forename: J S
authors.initials: JS
authors.lastname: Nelson
mesh_terms: D017679:Cryotherapy / Q000379:methods*; D006801:Humans; D066298:In Vitro Techniques; D053685:Laser Therapy / Q000379:methods*; D008954:Models, Biological; D019339:Port-Wine Stain / Q000601:surgery*; D019651:Plastic Surgery Procedures / Q000379:methods; D012867:Skin / Q000293:injuries*