Basic science: The cutting edge in optical diagnostics and therapeutics of tissues and cells

• Publisher: John Wiley and Sons
• Year: 2003
• Tongue: English
• Weight: 169 KB
• Volume: 32
• Category: Article
• ISSN: 0196-8092
• DOI: 10.1002/lsm.10159

✦ Synopsis

Background and Objective: Cryogen spray cooling (CSC) is used to minimize the risk of epidermal damage during pulsed laser treatment of port wine stain (PWS) birthmarks. However, higher cooling efficiencies are necessary to provide sufficient epidermal protection for patients with higher epidermal melanin concentrations. The objective of this work is to study the effects of spurt duration (Dt) on the instantaneous surface heat flux, q(t), resulting from CSC.

Study Design/Materials and Methods: We use a fast-response temperature measurement sensor made of a thin (20 mm) aluminum foil placed on top of a skin-like substrate with a miniature thermocouple in between. With this sensor, we measure real-time temperature variations at the surface during CSC. Using an inverse heat conduction (IHC) algorithm we compute q(t). Results: At a nozzle-to-surface distance (L) of 50 mm, q(t) is almost identical for all spurts longer than 30 ms, suggesting that spraying for a longer time may not be more beneficial from a cooling efficiency standpoint. Alternatively, q(t) measurements for spurts at L ¼ 20 mm exhibit an overall higher magnitude, but q(t) depends strongly on Dt. Conclusions: These differences can be associated with distinct droplet-surface interactions, which in turn affect the evaporation and boiling dynamics of liquid cryogen during CSC.