|
Port wine stain birthmark removal is based on selective photothermolysis. The most common technique utilizes 0.45 ms laser pulses at 585 nm wavelength. High incident energy doses are often needed to reach the ectatic blood vessels in dermis. This might induce changes in pigmentation or even epidermal necrosis. However, the epidermis can be protected by selectively cooling it down prior to laser exposure. Short cooling pulses ensure epidermal protection while preserving the temperature in dermis. Visible reflectance spectra of the birthmark are dependent on the melanin content, the blood volume and the scattering properties. these parameters also determine the fluence underneath the skin during laser exposure. Threshold fluence values can therefore be predicted for each specific lesion. Eight Scandinavian patients with red to purple macular port wine stains were treated with a pulsed dye laser at the energy density 6 J/cm2. Seven patients have developed hyperpigmentation in earlier treatments at this energy dose. One site in each lesion was cooled with a 20 ms cryogen spray immediately prior to laser exposure. Visible reflectance spectra were measured before and eight weeks after treatment. A simulation model based on diffusion approximation was used to estimate blood volume, skin pigmentation and scattering properties each time. The measured reflectance spectra, as well as the clinical observations, showed no significant differences between the cooled and uncooled sites. Estimated blood volume fractions and melanin pigmentations were about the same, and the short cooling spurts did not prevent hyperpigmentation. A light brown color was seen in both sites for 7 patients, and could be detected in the spectra for two patients. However, the estimated increases in pigmentation were small also for these patients. Calculated threshold fluence values were almost the same for cooled and uncooled sites after treatment.
|
