Modeling the effect of wavelength on the pulsed dye laser treatment of port wine stains

Abstract

To determine the influence of wavelength on the depth of vascular injury in port wine stains following pulsed dye laser treatment, we calculated fluence rates at wavelengths varying from 415 to 590 nm in a two-layer Monte Carlo model representing the epidermis and the dermis. Calculations were made for four different volumetric fractions of blood in the dermis: 0%, 1%, 5%, and 10%. The depth of the selective vascular injury was determined to be the depth at which the rate of temperature rise at some point within the vessel just equals that at the epidermal-dermal junction. This was maximal between 577 and 590 nm with the maximum shifted toward 590 nm for a greater dermal blood content and for larger vessels. The effect of greater epidermal pigmentation was not only to reduce the depth of vascular injury but to shift slightly the wavelength of the maximum vascular injury to a shorter wavelength.

A new Monte Carlo program for simulating light transport through Port Wine Stain skin

“…The anisotropy factors applied in this model were those introduced by van Gemert et al [21], and which have been used widely [19,[22][23][24][25][26][27].…”

Thermal Modelling for Laser Treatment of Port Wine Stains

“…The propagation of light in turbid media such as skin can be described by the radiative transport equation (Ishimaru, 1989) which cannot be solved analytically for tissue geometries. Techniques such as diffusion approximation (Gemert et al, 1997) and Beer's law (Verkruysse et al, 1993) have been used in the literature but they are limited to highly scattering or coherent radiance materials (Niemz, 1996). For skin tissue, the Monte-Carlo (MC) method, which offers a flexible approach to track the photon transportation in a biological tissue, is widely accepted now as an accurate method and has been used in modeling of laser surgery (Keijzer et al, 1991;Lucassen et al, 1996;Pfefer et al, 1996;Smith & Butler 1995;Wang et al, 1995& Wilson & Adam, 1983.…”

“…They found that the 585nm laser produced a deeper depth of vascular injury. The effects of various laser parameters such as pulsed duration, the repetition rate of pulses, the beam spot size, and the radiant energy fluencies on the outcomes of the laser surgery in PWS were systematically investigated (Gemert et al, , 1997Kienle & Hibst, 1995, 1997Verkruysse et al, 1993). In all these studies, the PWS layer is treated as homogeneous mixture of dermal tissue and blood of a given volumetric fraction.…”

“…Occasionally, the model with a single blood vessel was also used to test the clinic outcome of new treating protocols of laser PWS (Jia et al, 2006(Jia et al, , 2007. Concerns have been raised for possible lack of the scattering and shielding effects of numerous blood vessels in real PWS for those discrete blood vessel models (Tan et al, 1990;Verkruysse et al, 1993 The skin model with discrete blood vessels can provide direct visualization of heating of the blood vessels in laser PWS (Baumler et al, 2005;Shafirstein et al, 2004Shafirstein et al, , 2007Tunnell et al, 2003). For example, Smith and Butler (Smith & Butler, 1995) have shown that the blood vessels are heated up first during laser irradiation, and the dermis surrounding the vessel are then heated conductively by the high temperature vessels.…”

“…contents of melanin and hemoglobin (Verkruysse et al, 1993), respectively. The laser beam has a Gauss profile and the MLMC method discussed in Section 3 is used to quantify the energy deposition in various layers.…”