Modeling laser treatment of port wine stains with a computer-reconstructed biopsy.
OBJECTIVE
The efficacy of laser treatment of port wine stains (PWS) has been shown to be highly dependent on patient-specific vasculature. The effect of tissue structure on optical and thermal mechanisms was investigated for different pulse durations by using a novel theoretical model that incorporates tissue morphology reconstructed tomographically from a PWS biopsy.


METHODS
An optical-thermal numerical model capable of simulating arbitrarily complex, three-dimensional tissue geometries was developed. The model is comprised of (1) a voxel-based Monte Carlo optical model, (2) a finite difference thermal model, and (3) an Arrhenius rate process calculation to predict the distribution of thermal damage. Simulations based on previous computer-based reconstruction of a series of 6 microm sections from a PWS biopsy were performed for laser pulse durations (taup) of 0.5, 5.0, and 10.0 ms at a wavelength of 585 nm.


RESULTS
Energy deposition rate in the blood vessels was primarily a function of vessel depth in skin, although shading effects were evident. Thermal confinement and selectivity of damage were seen to be inversely proportional to pulse duration. The model predicted blood-specific damage for taup = 0.5 ms, vascular and perivascular damage for taup = 5 ms, and widespread damage in superficial regions for taup = 10 ms. The effect of energy deposition in the epidermis was most pronounced for longer pulse durations, resulting in increased temperature and extent of damage.


CONCLUSIONS
Pulse durations between 0.5 and 5 ms are likely optimal for the PWS analyzed. The incorporation of a tomographically reconstructed PWS biopsy into an optical-thermal model represents a significant advance in numerical modeling of laser-tissue interaction.
Pfefer
T J
TJ
Biomedical Engineering Program, The University of Texas at Austin, 78712, USA. pfefer@ccwf.cc.utexas.edu
Barton
J K
JK
Smithies
D J
DJ
Milner
T E
TE
Nelson
J S
JS
van Gemert
M J
MJ
Welch
A J
AJ
D000328:Adult; D001706:Biopsy; D003198:Computer Simulation; D062109:Dermatologic Surgical Procedures; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D053685:Laser Therapy; D019339:Port-Wine Stain / Q000473:pathology / Q000601:surgery*; D012867:Skin / Q000473:pathology