Selective Photothermolysis of Blood Vessels Following Flashlamp-Pumped Pulsed Dye Laser Irradiation: In Vivo Results and Mathematical Modelling Are in Agreement

Abstract

Laser therapy using the pulsed dye laser is the standard treatment for port-wine stains (PWS). But the mechanism of action has not been elucidated completely, yet. The dorsal skin-fold chamber model in hamsters was used to investigate the effects of laser treatment (lambda(em)=585 nm; pulse duration: 0.45 ms; fluence: 6 J per cm2) on blood vessels. Vessels (n=3394) were marked with FITC dextran (MW 150 kDa) and diameters (2-186 microm) were measured using intravital fluorescence microscopy up to 24 h following irradiation. Histology (H&E, TUNEL, CD31) was taken 1 or 24 h after irradiation. The experimental results were compared with the predictions of a mathematical model based on the finite-element method. Following irradiation treatment the number of unperfused vessels decreases with decreasing vessel diameter in vivo. Histology indicated a restriction of tissue injury to the irradiated area after 1 h. Blood vessels contained aggregated red blood cells. After 24 h tissue damage occurred also outside the irradiated area and thrombus formation was visible. These results were in agreement with the mathematical calculations. In addition to initial physical effects after pulsed dye laser treatment delayed biological processes contribute significantly to the reduction of perfused blood vessels. Because of incomplete photocoagulation of smaller blood vessels (diameter 2-16 microm) a complete bleaching of PWS seems to be unlikely.

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

“…These are results from computations with the Monte Carlo method. Using the diffusion approximation, the average temperatures for the same vessel diameters (10,20,30,40,50, and 60 mm, and 200 mm depth) and 1 J/cm 2 laser fluence are 63, 81, 84, 80, 74, and 708C. These results are comparable to the Monte Carlo computations.…”

“…Clinical studies evaluating the relationship between therapeutic outcome and PWS morphology and anatomic location have found that smaller diameter and deeply located vessels respond poorly to laser treatments: Fiskerstrand et al [7] reported a PWS vessel mean diameter and depth of approximately 20 and 250 mm, respectively, in patients that responded poorly to PDL; Sivarajan and Mackay [8] reported a reduction in vessel mean diameter from 70 to 40 mm and increased vessel depth from 70 to 85 mm after PDL treatment; the same authors [9] also reported that vessels with diameters of 10-50 mm remained after PDL treatment, while vessels with larger diameters were successfully photocoagulated. Babilas et al [10] reported incomplete photocoagulation in vessels of 2-16 mm diameter after PDL irradiation of hamster microvasculature.…”

Microvascular blood flow dynamics associated with photodynamic therapy, pulsed dye laser irradiation and combined regimens

“…First, and perhaps most significant, is the limited ability of the PDL to remove small, superficial vessels (<20 mm) [3,4]. Second, considerable light absorption by epidermal melanin limits the maximum permissible radiant exposure that can be used safely.…”

The effects of intense pulsed light (IPL) on blood vessels investigated by mathematical modeling

“…In order to achieve this, we modified our mathematical model of selective photothermolysis of portwine stains used in a previous study [14]. This model utilized finite element methods to solve the diffusion approximation of light tissue interaction and was successfully shown in animal model to be well correlated with clinical outcomes [14][15][16]. In the current study, we investigated the applicability of mathematical modeling for selective photothermolysis to multiple wavelengths in a simultaneous fashion.…”