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The pulsed dye laser is the most efficient laser to treat port wine stains. Mathematical modeling predicts that the incident optical fluence required to coagulate small sized and/or deeply located vessels is larger than the threshold value for epidermal damage. Dynamic cooling has been reported to prevent epidermal damage caused by the absorption of laser energy in melanin. Further on, this cooling technique has proved to reduce the pain associated with laser therapy. The aim of our study was to examine possible clinical advantages of dynamic cooling. A flash lamp pumped dye laser emitting at 585 nm wavelength with pulse duration of 0.45 ms and a 5 mm diameter spot-size was used. In 12 port wine stains pairs of test sites were exposed to laser pulses with incident fluences of 6.0 to 10.0 J/cm2. In all stains one of the sites in each pair received 20 ms cryogen spurts immediately prior to laser admission. In the cooled areas laser induced pain was significantly reduced, and the time period with skin discoloration was shortened by an average of 5 days. Post treatment hyperpigmentation was not prevented. Future studies will aim at improving the cooling technique in order to achieve optical protection of the epidermis.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

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.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The visual appearance of port-wine stain lesions is often a red to purple color due to an enlarged blood volume in the upper dermis. The purpose of the treatment is to re-establish normal skin coloration. Visual reflectance spectra should therefore, in principle, contain all relevant information about the lesion. The influence on the spectra from the different tissue parameters, such as melanin, blood content and scattering, is rather composite. However, a simple mathematical model can give a good understanding of the relevance of the different components. This knowledge can be used to optimize the laser treatment of port-wine stain. In vivo reflectance spectra were obtained using an integrating sphere spectrophotometer. A simple mathematical model based on the diffusion approximation was used to simulate port- wine stain and normal skin reflectance spectra. The absorption coefficients of epidermis and dermis are mainly due to melanin and blood. These parameters were measured in separate in vivo experiments and obtained from skin biopsies. The scattering coefficients were based on reported values. Simulated reflectance spectra show good agreement with the measured ones. Even though the diffusion model has limited validity for wavelengths shorter than 600 nm, the simulated spectra from 450 to 600 nm give a qualitative understanding of the influence of the tissue parameters. The results show that dark red to almost dark grey port-wine stains contain enlarged blood fraction in the entire upper dermis. The red port-wine stains appear when the abnormal density of blood is confined to a thin layer. High amount of epidermal melanin results in reduced reflectance throughout the visible spectrum. The characteristic spectrum due to the blood is suppressed. The reflectance spectra are strongly dependent on the dermal and epidermal scattering coefficient; even minor changes as naturally occurring with age, might have a significant impact. A permanently reduced scattering coefficient might result in a reddish coloration even when a normal blood content is restored. Correlation between measured and simulated spectra give a good understanding of the importance of the parameters determining the visual appearance of port-wine stain.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Visible reflectance spectra of human skin might serve as a valuable tool for determining blood volume and pigmentation. They can therefore be used to evaluate the response to various skin treatments such as, e.g., port-wine stain therapy. A fiber-optic system is preferable for clinical evaluation of the therapeutic response due to its higher flexibility. Diffuse reflectance spectra obtained using a fiber system are compared with the corresponding spectra from an integrating sphere system. The results show that the most accurate reflectance spectra are obtained using the integrating sphere set-up. The aperture should then be much larger than the optical penetration depth of the skin. The system will then collect all the reflected light from superficial and deeper layers, and this enables a qualitative comparison between the wavelengths. However, the size and localization of many dermal lesions limit its use. In these cases the fiber-optic system is preferable. Light with an optical penetration depth shorter than the distance between the excitation and collecting fibers is, however, favorized. Normal dermis has typically a penetration depth of 600 micrometers and 2000 micrometers for, respectively, green/yellow and red light. Consequently, the collection efficiency of a typical fiber-optic system with a distance of 100 - 200 micrometers between the emitting and collecting fibers, will be higher in the green/yellow than in the red part of the spectrum. It is, however, important to remember that the relevant parameter is the change in reflectance at each particular wavelength, rather than comparison between the wavelengths. When such a comparison is required, the spectra collected by the fiber-optic system can be calibrated. The more accurate integrating sphere system is maybe preferable in a research laboratory environment, whereas the more flexible fiber-optic system is the most applicable for use in the clinic.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Selective photothermolysis with pulsed lasers is presumably the most successful therapy for port wine stain birthmarks (flammeus nevi). Selectivity is obtained by using an optical wavelength corresponding to high absorption in blood together with small absorption in tissue. Further on, the pulse length is selected to be long enough to allow heat to diffuse into the vessel wall, but simultaneously short enough to prevent thermal damage to perivascular tissues. The optimal wavelength and pulse length are therefore dependent on vessel diameter, vessel wall thickness and depth in dermis. The present work, that is based on analytical mathematical modeling, demonstrates that in the case of a 0.45 ms long pulse at 585 nm wavelength vessels of diameter in the range of 40 - 60 micrometers require minimum optical fluence. Smaller vessels require higher fluence because the amount of heat needed to heat the wall then becomes a substantial fraction of the absorbed optical energy, and larger vessels require higher dose because the attenuation of light is blood prevents the blood in central part of the lumen to participate in the heating process. Further on, it is shown that the commonly used dose in the range of 6 - 7 J/cm2 is expected to inflict vessel rupture rather than thermolysis is superficially located vessels. The present analysis might serve to draw guide lines for a protocol where the optical energy, wavelength and pulse length are optimized with respect to vessel diameter and depth.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The clinical objective in treatment of port wine stains by laser heating is to maximize thermal damage tothe blood vessels without introducing thermal damage to the normal overlying epidermis. The rationale of dynamic cooling is to protect the epidermis from thermal damage by selectively cooling this layer immediately before delivering the laser pulse. This work discusses the thermal dynamics of melanosomalheating by a laser when the epidermis is cooled by millisecond cryogen spurts prior to the laser pulse.Key words: epidermis, cryogens, dye laser, melanin, mathematical modeling. Introduction The principle of laser induced selective photothermolysis is to induce thermal damage to specific targets(e.g., microvessels or cells), in such a manner that the temperature of the surrounding normal tissue ismaintained below the threshold for damage' .Selectivity is obtained by choosing the proper wavelengthtogether with a pulse duration that is equal to or smaller than the time required for heat to diffuse acrossthe target. The technique is used in clinical procedures for the treatment of benign cutaneous lesions suchas port wine stains. Port wine stain is a congenital birthmark consisting of an abnormal density of blood

Photothermal tomography (PTT) is applied to characterize diameter and depth of subcutaneous chromophores such as blood vessels that comprise port wine stain (PWS) birthmarks. PTT uses a fast infrared detector array to measure temperature rises in a PWS induced by pulsed laser radiation. A PTT record of PWS in response to pulsed laser exposure is composed of a sequence of infrared emission frames, each consisting of elevated temperature regions indicative of subcutaneous blood vessel heating. An analytic expression for recorded infrared emission frames is derived as a convolution integral of a PTT point spread function and the 3- D temperature distribution in the PWS immediately following laser exposure. Diameters of blood vessels comprising the PWS are best resolved in early infrared emission frames when radial heat diffusion is relatively small.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.