Modelling the assessment of port wine stain parameters from skin surface temperature following a diagnostic laser pulse

Abstract

Background and Objective Laser treatment of port wine stains (PWS) has become an established clinical modality over the past decade. However, in some cases full clearance of the PWS cannot be achieved. To improve the clinical results, it is necessary to match the laser treatment parameters to the PWS anatomy on an individual patient basis. Therefore, knowledge of the PWS structure is of great importance. The objective of this study is to describe a diagnostic method to assess the PWS blood vessels depth and diameter from the skin surface temperature‐time course following a diagnostic laser pulse. Study Design/Materials and Methods The Monte Carlo (MC) method was used to calculate the deposited laser energy into a port wine stain skin model following irradiation by a diagnostic laser pulse at 577 nm. The heat equation was solved numerically, using the deposited energy profile as the source term, yielding the temperature‐time course at the skin surface. Subtraction of “bloodless” skin signal from that of the skin containing blood vessels gives us the net contribution of a heated dermal blood vessel to the skin surface temperature‐time behaviour. Results The net blood vessel signal shows heat‐diffusion behaviour and was found to be sensitive to the dermal blood vessel depth and diameter. The time delay for the peak signal temperature to occur depends quadratically on the blood vessel depth. The peak temperature relates linearly to the blood vessel diameter. The degree of epidermal melanin content can also be determined from the immediate temperature rise of the signal. Conclusion The proposed method easily enables assessment of the blood vessel depth and diameter as well as the epidermal melanin content in a skin model. The method can be applied to a real PWS when using the adjacent normal skin as a reference. Lasers Surg. Med. 20:179–187, 1997. © 1997 Wiley‐Liss, Inc.

A new mathematical approach to the diffusion approximation theory for selective photothermolysis modeling and its implication in laser treatment of port‐wine stains

“…Temperatures of 80-1008C are sufficient to achieve significant coagulation as it is an accumulative process (Figs. [8][9][10], once the activation energy is overcome. Furthermore, it is unlikely that the blood will boil in laser treatments of PWS, because, if this were the case, we would expect to find reports of scarring and burning as side effects associated with FPDL treatment of PWS.…”

“…In all of these models, the skin is considered an optically turbid medium. Light propagation in a turbid medium, such as human tissue, can be modeled through an analytical solution of diffusion theory and Monte Carlo (MC) simulations [1][2][3][4][5][6][7][8][9][10]. Whereas MC is an accurate method to predict light distribution in media, diffusion theory is an approximation.…”

“…The probability that photons will be scattered, absorbed, or transmitted at each point of time and space is calculated through density function. Photon packages of 10 4 -10 6 and voxel sizes of 8,000 mm 3 or 24 mm 3 have been used in MC simulations to calculate the photon distribution within 1-2 mm 3 of irradiated tissue [4,5,8,11,12]. Following the MC simulation, thermal distribution is calculated by finite differences [4,8,11,12].…”

Quantitative analysis of optical properties of flowing blood using a photon-cell interactive Monte Carlo code: effects of red blood cells’ orientation on light scattering

“…For developing a photon propagation model in blood based on MC simulation, the phase function derived using the Mie, Rayleigh-Gans, or straight-ray theory has been developed and utilized. [13][14][15] The optical simulation using MC codes, [16][17][18][19][20][21][22][23][24][25][26] however, treats red blood cells (RBCs) as points in the space, hence it is difficult to determine cell orientation in the space. The scattering by RBCs depends on the incident photon direction because RBCs have a non-spherical biconcave shape.…”

Estimation of Heat Transfer Coefficient of Cryogen Spray Cooling with Alifanov's Iterative Regularization Method

“…Port wine stains are pink to purple vascular skin lesions characterized by an enlarged number or enlarged diameter of dermal blood vessels [1,2]. Laser treatment of PWS is based on selective heat deposition into the target dermal blood vessels to produce irreversible thermal damage in these target vessels.…”