Laser surgery of port wine stains using local vaccum pressure: Changes in calculated energy deposition (Part II)

Abstract

Background and Objectives: Application of local vacuum pressure to human skin during laser irradiation results in less absorption in the epidermis and more light delivered to targeted vessels with an increased blood volume. The objective of the present numerical study is to assess the effect of applying local vacuum pressure on the temperatures of the epidermis and small vessels during port wine stain (PWS) laser treatment. Study Design/ Materials and Methods: Mathematical models of light deposition and heat diffusion are used to compute absorbed energy and temperature distributions of skin and blood vessels with different diameters (10-60 mm) at various depths (200-800 mm) exposed to laser irradiation under atmospheric and vacuum pressures. Results: Under 50 kPa (15 in Hg) vacuum pressure, peak temperatures at the inner walls of small diameter vessels (10-30 mm) located 200-300 mm below the skin surface are %108C higher than those under atmospheric pressure, and peak temperatures in the epidermis of patients with skin phototype II are %58C lower. In patients with darker skin phototype (IV), the peak temperature at the inner wall of a 10 mm diameter vessel located 200 mm below the skin surface is %58C higher than that under atmospheric pressure, and the peak temperature in the epidermis is %108C lower. Conclusions: Additional energy deposition in a larger blood volume permits higher temperatures to be achieved at vessel walls in response to laser irradiation. While more energy is deposited in every vessel, temperature gains in small diameter vessels (10-30 mm) are greater, increasing the likelihood of irreversible thermal damage to such vessels. In addition, temperatures in the epidermis decrease because less energy is absorbed therein due to reduced epidermal thickness and concentration of melanin per unit area.

An Overview of Three Promising Mechanical, Optical, and Biochemical Engineering Approaches to Improve Selective Photothermolysis of Refractory Port Wine Stains

“…After this time interval, however, both BVF and D v rose from 1.3 to 10.5% and from 9.5 to 20.0  μ m, respectively, reaching a plateau after ~9 s (Fig. 3c) 3,29,49. Moreover, the kinetics of BVF and D v during the application of hypobaric pressure were characterized by a fast rate increase followed by a slower rate increase.…”

“…A 10- μ m-diameter blood vessel was positioned at 200  μ m below the skin surface. Data taken from Franco et al 49. Differences in blood (e) and vessel wall temperatures (f) at the end of the laser pulse (585-nm wavelength, 0.45-ms pulse duration, 1-J/cm 2 radiant exposure, 10-mm spot size) at hypobaric and atmospheric pressures, plotted as a function of vessel diameter for different vessel depths (legend).…”

“…Franco et al 49. employed a numerical model of light and heat diffusion that yielded three important aspects of laser–tissue interactions at hypobaric pressure.…”

Finite element analysis of thermal and acoustic processes during laser tattoo removal

“…1) to evaluate the effects of anisotropic light scattering and to evaluate the absorbed energy of each ink granule. Light transport was assumed to be time independent as it occurs in considerably less time than thermal conduction 16 where u is the fluence rate within each element of the model, D is the diffusion coefficient, µ a represents the absorption coefficient and f is the source term.…”

Real-time measurement of skin erythema variation by negative compression: pilot study

“…Skin color information has been widely used as an useful parameter to evaluate skin lesions in dermatology, cosmetology, orthopedic and plastic surgery, and alternative medicine. [1][2][3][4][5][6][7][8][9] Skin color is primarily determined by melanin and hemoglobin contents, which can indicate the presence or absence of cutaneous pathology or patient response to therapy. 8,10,11 Melanin and hemoglobin contents have been indirectly measured using the melanin and erythema index (EI) in the absence of skin deformation.…”