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Numerical modeling of spray cooling-assisted dermatologic laser surgery for treatment of port wine stains
 

Summary: Numerical modeling of spray cooling-assisted dermatologic
laser surgery for treatment of port wine stains
Walfre Francoa,b, Rong Zhangb, J. Stuart Nelsonb, and Guillermo Aguilara,b
aDept. of Mechanical Engineering, University of California, Riverside, CA 92521
bBeckman Laser Institute Medical Clinic, University of California, Irvine, CA 92612
ABSTRACT
Cryogen spray cooling (CSC) provides thermal protection to the epidermis during dermatologic laser surgery
(DLS) for removal of port wine stain (PWS) birthmarks. The objectives of this paper are: to improve the thermal
modeling of skin undergoing CSC-assisted DLS for PWS treatment; and, to address the effect of temporal and
lateral variations in surface heat transfer during CSC on epidermal protection. The finite element method is used
to solve the two-dimensional light and heat diffusion equations in a skin-cross section composed by epidermis,
dermis and two blood vessels. Thermal conductivities of each biological structure are modeled as temperature
dependent functions. The model accounts for the latent heat of fusion and vaporization, and temporal and spatial
thermal variations--due to the inherent non-homogeneous nature of sprays--in surface cooling. Thermal damage
due to laser irradiation is evaluated by an Arrhenius integral model. For a 60 ms cryogen spurt, temperature
maps of epidermis show that at the end of the spurt there are significant temperature differences, which resulted
in epidermal damage after a 5 J/cm2
0.45 ms laser pulse at 585 nm on light color skin type. A 60 ms delay
between end of spurt and laser onset produced a relative more homogeneous temperature distribution at the
epidermis, and, subsequently, a more effective CSC-DLS for which only the blood vessels were thermally damaged.

  

Source: Aguilar, Guillermo - Department of Mechanical Engineering, University of California at Riverside

 

Collections: Engineering