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Although epidermal melanin content has been quantified non-invasively using visible reflectance spectroscopy (VRS), there is currently no way to determine melanin distribution in the epidermis. We have developed a photoacoustic probe that uses a Q-switched, frequency-doubled Nd:YAG (neodymiurn, yttrium, aluminum, garnet) laser operating at 532 nm to generate acoustic pulses in skin in vivo. The probe contained a piezoelectric element that detected photoacoustic waves that were then analyzed for epidermal melanin content using a photoacoustic melanin index (PAMD). Melanin content was compared between results of photoacoustics and VRS. Spectra from human skin were fitted to a model based on diffusion theory that included parameters for epidermal thickness, melanin content, hair color and density, and dermal blood content. Ten human subjects with skin phototypes I-VI were tested using the photoacoustic probe and VRS. A plot of PAMI v. VRS showed a good linear fit with r2 = 0.85. Photoacoustic and VRS measurements are shown for a human subject with vitiligo, indicating that melanin was almost completely absent. We present preliminary modeling for photoacoustic probe design and analysis necessary for depth profiling of epidermal melanin.

Background and Objective Monitoring dynamic changes during laser induced photothermolysis of vascular skin lesions is essential for obtaining an optimal therapeutic result. Rapid photoinduced thermal damage occurs at a threshold temperature of about 70°C. It is therefore, relevant to identify markers to indicate if this threshold temperature has been reached. Methemoglobin, which is formed by a photo-induced oxidation of hemoglobin, indicates that the temperature has reached this threshold value. This study presents a proof of concept of a method for monitoring the in vivo presence of methemoglobin immediately after laser exposure. Study Design/Materials and Methods The present study was designed to investigate the in vivo temperature dependence of hemoglobin absorption in the 450–800 nm spectrum range. In vivo diffuse reflectance measurements of port-wine stain (PWS) and telangiectasia were performed prior to, and immediately after, laser treatment with a pulsed dye laser (PDL) at 585 nm wavelength. Results In vivo measurements following laser treatment of vascular skin lesions showed an immediate increase in the optical absorption of blood. This effect, caused by thermal stress, is a result of an increased dermal blood volume fraction and methemoglobin formation. The effect is light dose dependent, and reflectance spectra revealed methemoglobin formation in patients treated with fluences above 5 J/cm2 at 585 nm wavelength. Conclusions It was proved that methemoglobin can be measured in vivo by reflectance spectroscopy. Measurements of the average methemoglobin concentrations immediately after laser exposure may be a valuable diagnostic tool to verify that the blood temperature has been sufficiently high to induce thermal damage to the vessel wall. Lasers Surg. Med. 34:414–419, 2004. © 2004 Wiley-Liss, Inc.

Background and Objective Treatment of port wine stains (PWS) by photothermolysis can be improved by optimizing laser parameters on an individual patient basis. We have studied the critical role of pulse duration (tp) on the treatment efficacy. Study Design/Materials and Methods The V-beam laser (Candela) allowed changing tp over user-specified discrete values between 1.5 and 40 milliseconds by delivering a series of 100 microsecond spikes. For the 1.5 and 3 millisecond pulses, three spikes were observed at intervals tp/2 and for tp ≥ 6 milliseconds, four spikes separated by tp/3. The ScleroPlus laser (Candela) has a smooth output over its fixed 1.5 milliseconds duration. Blood vessels in the chick chorioallantoic membrane (CAM) were irradiated at fixed wavelength (595 nm), spot size (7 mm), radiant exposure (15 Jcm−2), and at variable tp. The CAM contains an extensive microvascular network ranging from capillaries with diameter D 0.05). Conclusions The difference between initial arteriole and venule damage could be explained by the threefold higher absorption coefficient at 595 nm in (oxygen-poor!) arterioles. In human patients, PWS consist of ectatic venules (characterized by higher absorption), so that these considerations favor the use of 595-nm irradiation for laser photothermolysis. For optimal treatment of PWS it is proposed that tp be between 0.1 and 1.5 milliseconds. This is based on a modified relaxation time τd′, defined as the time required for heat conduction into the full thickness of the vessel wall, which is assumed to have a thickness ΔD ≈ 0.1D. The corresponding τd′ will be a factor of about six smaller than given in the literature. For vessels with D between 30 and 300 μm, τd′ ranges from 0.1 to 1.5 milliseconds. Lasers Surg. Med. 30:160–169, 2002. © 2002 Wiley-Liss, Inc.

Background and Objective: Dynamics of cryogen spray deposition, water condensation and frost formation is studied in relationship to cooling rate and efficiency of cryogen spray cooling (CSC) in combination with laser dermatologic surgery. Study Design/Materials and Methods: A high-speed video camera was used to image the surface of human skin during and after CSC using a commercial device. The influence of ambient humidity on heat extraction dynamics was measured in an atmosphere-controlled chamber using an epoxy block with embedded thermocouples. Results: A layer of liquid cryogen may remain on the skin after the spurt termination and prolong the cooling time well beyond that selected by the user. A layer of frost starts forming only after the liquid cryogen retracts. Condensation of ambient water vapor and subsequent frost formation deposit latent heat to the target site and may significantly impair the CSC cooling rate. Conclusion: Frost formation following CSC does not usually affect laser dosage delivered for therapy of subsurface targets. Moreover, frost formation may reduce the risk of cryo-injury associated with prolonged cooling. The epidermal protection during CSC assisted laser dermatologic surgery can be further improved by eliminating the adverse influence of ambient humidity. Lasers Surg. Med. 28:469‐476, 2001. fl 2001 Wiley-Liss, Inc.

Cryogen spray cooling (CSC) has been used for selective epidermal cooling of human skin during laser therapy of patients with port wine stain (PWS) birthmarks. Unfortunately, current commercial CSC devices do not provide optimal cooling selectivity and, therefore, provide insufficient epidermal protection for some PWS patients. To assist in the development of improved atomizing nozzle designs, a reliable method to quantify the CSC heat flux is needed. We introduce a novel method to determine the heat flux (q/sub s/) and heat transfer coefficient (h) at the surface of a sprayed object, based on measurements of steady-state temperature gradients along a thin copper rod during continuous cryogen spraying. For an atomizing nozzle of inner diameter d/sub N/ = 0.7 mm, we found that q/sub s/ varies from 15 to 130 W/cm/sup 2/ and h increases nonlinearly from 15000 to 35000 W/m/sup 2/.K in the explored range of surface temperatures (T/sub s/, from -32 to -7/spl deg/C). Values of q/sub s/ obtained with a wider diameter nozzle (d/sub N/ = 1.4 mm) are approximately twice as large than those of the narrow nozzle. The corresponding values of h are significantly higher (32000-40000 W/m/sup 2/.K) and almost independent of T/sub s/ within the same temperature range. When combined with fast flashlamp photography (FFLP) of spray shapes and sprayed surfaces, the results demonstrate that the liquid cryogen layer, as deposited by finely atomized sprays from narrower nozzles, can significantly impair q/sub s/. In contrast, the higher-momentum impact of coarser sprays from wider nozzles reduces the thickness of the liquid layer in the impact area and/or enhances convection within it, yielding a larger q/sub s/.

The epidermal melanin content affects most dermatologic treatments involving light, and can limit the therapeutic success significantly. Therefore, knowledge of the optical properties of skin is required. This study investigates how the concentration of melanin influences visible reflectance spectra of skin and the relationship to threshold radiant energy fluence for melanosomal or melanocyte destruction. Reflectance spectra were measured at 28 pigmented human skin sites in vivo. For Asian and Caucasian subjects, measured reflectance values varied over the same range, while significantly lower values were recorded for African individuals. Epidermal melanin absorption coefficients measured at 694 nm were about 2500 m-1 for African, and 300–1200 m-16 for Caucasian and Asian skin. Twenty-five skin sites were exposed to ruby laser pulses (694 nm), where the pulse duration was long enough to allow heat diffusion between melanosomes. Hypopigmentation occurred, on average, at 12 and 26 J cm-2 for sun-exposed and sun-protected white skin, respectively, while slightly lower threshold values resulted from the measured spectra. As visible reflectance spectra reveal information regarding skin pigmentation and individual threshold doses for melanosomal damage, a use as a diagnostic tool in various dermatological laser treatments is apparent.

When a cryogen spurt is applied to the skin surface for an appropriately short period of time (on the order of tens of milliseconds), the spatial distribution of cooling remains localized in the normal overlying epidermis, while leaving the temperature of the deeper port wine stain (PWS) blood vessels unchanged. Furthermore, cooling continues after pulsed laser exposure as cryogen remaining on the surface evaporates and removes heat deposited by light absorption in epidermal melanin. An additional advantage of dynamic cooling is a reduction in the level of pain and discomfort associated with flashlamp-pumped pulsed dye laser therapy of PWS. Preliminary clinical studies and supporting theoretical calculations demonstrate the feasibility of selective epidermal cooling while achieving photothermolysis of blood vessels during pulsed laser treatment of PWS.

We describe a non-contact method using infrared radiometry to determine lateral physical dimensions of laser heated subsurface chromophores in biological materials. An imaging equation is derived that relates measured radiometric temperature change to the reduced two-dimensional temperature increase of laser heated chromophores. From measured images of radiometric temperature change, the lateral physical dimensions of chromophores positioned in an in vitro model of human skin are determined by deconvolution of the derived imaging equation using a non-negative constrained conjugate gradient algorithm. Conditions for optimum spatial resolution are found by analysis of a derived radiometric transfer function and correspond to superficial chromophores and/or weak infrared absorption in a laser irradiated biological material. Analysis indicates that if the infrared attenuation coefficient is sufficiently small (i.e., less than 10mm-1), infrared radiometry in combination with a deconvolution algorithm allows estimation of lateral physical dimensions of laser heated subsurface chromophores in human skin.

Monte Carlo simulation of laser energy deposition in a port-wine stain (PWS) skin model and numerical solution of the thermal diffusion equation have been used to calculate threshold energies for thermal injury of PWS blood vessels for different vessel sizes and laser pulse durations. It has been assumed that an average vessel temperature rise of 65 ‡C causes thermal injury to the blood vessel. The result is that for a certain combination of wavelength, pulse duration and incident energy density, only a limited range of blood vessel sizes can be injured optimally. Higher energy densities are required to injure smaller vessels with the same pulse duration, spot size and wavelength. This gives support to the mechanisms of selective photothermolysis suggested previously by Anderson and Parrish, although their model was based on the cooling behaviour of instantaneously heated vessels. The authors hypothesize that different laser parameter settings that match the individual PWS vessel anatomy during treatment will be used in the future, instead of many treatments with the same laser parameters. This could lead to less treatment sessions and to an improved predictability of clinical results.

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 tissues. 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 optical wavelength and pulse length are therefore dependent on vessel diameter, vessel wall thickness and depth in dermis. The present work demonstrates that in the case of a 0.45 ms long pulse at 585 nm wavelength, vessels of 40–60Μm require minimum optical fluence. Smaller vessels require higher fluence because the amount of heat needed to heat the wall becomes a substantial fraction of the absorbed optical energy. Larger vessels also require a higher dose because the attenuation of light in blood prevents the blood in the centre of the lumen from participating in the heating process. It is shown that the commonly used optical dose in the range of 6–7 J cm−2 is expected to inflict vessel rupture rather than thermolysis in superficially located vessels. The present analysis might serve to draw guidelines for a protocol where the optical energy, wavelength and pulse length are optimized with respect to vessel diameter and depth in dermis.

The clinical objective in laser treatment of port-wine stains (PWS) is to induce selective photothermolysis of subsurface blood vessels without damaging the overlying epidermis. This paper investigates the effectiveness of ‘dynamic’ cooling, where a cryogen is sprayed on the skin surface for an appropriately short period of time, to eliminate epidermal thermal injury during laser treatment of PWS. Comparative measurements of radiometric surface temperature from cooled and uncooled laser irradiated (585 nm) PWS sites, and theoretical predictions of temperature distributions within skin in response to dynamic cooling in conjunction with laser irradiation are presented. Rapid reduction of skin surface temperature and localization of cooling the epidermis are obtained when a cryogen is sprayed on skin prior to laser irradiation. Successful blanching of the PWS without thermal injury to the overlying epidermis is accomplished.

The relationship between photothermal damage to blood vessels of diameter,d, and laser pulse duration,t p, was verified in a series of studies using the chick chorioallantoic membrane (CAM). A total of 879 individual CAM blood vessels (d=50–130μm) was irradiated, using a laser pulse duration of 0.45 or 10 ms. Laser-induced vascular damage was observed in real time, recorded on videotape, and evaluated in a double-blind fashion. Permanent damage was confirmed by inspection 24 h after laser exposure. Under the conditions of this experiment, only when laser pulse durations are approximately equal to the estimated thermal relaxation times (τ) of the CAM microvessels can the critical core intravascular temperature, necessary to destroy vessels irreversibly, be achieved and sustained for sufficient time. Shorter pulse durations are more effective for damaging smaller blood vessels; conversely, longer pulse durations are more effective for damaging larger diameter vessels.

The ability to control the degree and spatial distribution of cooling in biological tissues during a thermally mediated therapeutic procedure would be useful for several biomedical applications of lasers. The authors present a theory based on the solution of the heat conduction equation that demonstrates the feasibility of selectively cooling biological tissues. Model predictions are compared with infrared thermal measurements of in vivo human skin in response to cooling by a cryogen spurt. The presence of a boundary layer, undergoing a liquid-vapour phase transition, is associated with a relatively large thermal convection coefficient ( approximately=40 kW m-2 K-1), which gives rise to the observed surface temperature reductions (30-40 degrees C). The degree and the spatial temporal distribution of cooling are shown to be directly related to the cryogen spurt duration.

Individual blood vessels in the chick choriallantoic membrane were selectively coagulated through photothermolysis, using pulsed laser irradiation at 585 nm. Pulse durations were chosen to be 0.45 ms and 10 ms, which correspond to the thermal relaxation times in blood vessels of 30 microns and 150 microns diameter, respectively. The short pulses, at a light fluence F = 3 Jcm-2, caused permanent occlusion of vessels of 40 microns diameter or less, whereas larger caliber vessels (60-120 microns) required F = 4-5 Jcm-2. The long-duration pulses, at F = 7 Jcm-2, caused coagulation of the larger diameter vessels; the small-caliber vessels and capillaries showed resistance to photothermolysis and required multiple exposures to achieve coagulation. The fluence versus diameter (F versus d) relationship for coagulation was calculated for the two pulse durations. The energy deposited in a cylindrical absorber of diameter d by an optical field, incident perpendicular to the vessel, was expressed analytically and compared with the energy required to coagulate a blood vessel of the same lumen dimeter. When thermal diffusion is incorporated into the model, our findings can be accounted for quantitatively. This information will be of use for improving the laser treatment of port wine stains and other vasculopathies. A surprising observation was that arterioles were damaged at lower incident energy densities than venules having the same lumen diameter, despite the fact that absorbance in oxygen-rich and oxygen-poor blood is the same at 585 nm.

Experimental results for the optical distribution and temperature rise during laser irradiation of tumors are presented. The experimental conditions are chosen to simulate laser irradiation of ocular tumors. The tumor models are human retinoblastoma heterotransplanted in athymic mice, murine mammary carcinoma in C3H/HEJ mice, and B16 melanotic melanoma in C57/BL6 mice. The experimental results are discussed in terms of a mathematical model where the thermal distribution is calculated from the bioheat transfer equation, and the optical distribution is determined according to diffusion theory.

Human skin prepared with an optical clearing agent manifests reduced scattering as a result of de-hydration and refractive index matching. This has potentially large effects for laser therapies of several skin lesions such as port wine stain, hair removal and tattoo removal. With most topically applied clearing agents the clearing effect is limited because they penetrate poorly through the intact superficial skin layer (stratum corneum). Agent application modi other than topically are impractical and have limited the success of optical clearing in laser dermatology. In recent reports, however, a mixture of lipofylic and hydrofylic agents was shown to successfully penetrate through the intact stratum corneum layer which has raised new interest in this field. Immediately after application, the optical clearing effect is superficial and, as the agent diffuses through the skin, reduced scattering is manifested in deeper skin layers. For practical purposes as well as to maximize therapeutic success, it is important to quantify the reduced scattering as well as the trans-cutaneous transport dynamics of the agent. We determined the time and tissue depth resolved effects of optically cleared skin by inserting a microscopic reflector array in the skin. Depth dependent light intensity was measured by quantifying the signal of the reflector array with optical coherence tomography. A 1-dimensional mass diffusion model was used to estimate a trans-cutaneous transport diffusion constant for the clearing agent mixture. The results are used in Monte Carlo modeling to determine the optimal time of laser treatment after topical application of the optical clearing agent.

Background and Objectives: Hypervascular skin lesions (HVSL) are treated with medical lasers characterized by a variety of parameters such as wavelengthl, pulse duration tp, and radiant exposure E that can be adjusted for different pathology and blood vessel size. Treatment parameters have been optimized assuming constant optical properties of blood during laser photocoagulation. However, recent studies suggest that this assumption may not always be true. Our objective was to quantify thermally induced changes in blood that occur during irradiation using standard laser parameters. Study Design/Materials and Methods: Glass capillary tubes (diameter D ¼ 100, 200, and 337 mm) filled with fresh or hemolyzed rabbit blood were irradiated once at l ¼ 585, 595, or 600 nm, tp ¼ 1.5 milliseconds; and also atl ¼ 585 nm, tp ¼ 0.45 milliseconds. E was increased until blood ablation caused formation of permanent gas bubbles. In a corroborative study, human blood was heated at 508C and absorbance spectra were measured as a function of time. Results: Threshold radiant exposure, Ethresh, for gas bubble formation was found not to depend on l, which might be surprising in view of the 10-fold lower absorption coefficient at 600 nm as compared to 585 nm. The spectroscopic study revealed heat-induced changes in blood constituent composition of hemoglobins (Hb) from initially 100% oxyhemoglobin (HbO2) to deoxyhemoglobin (HHb) and, ultimately, methemoglobin (metHb) as the major constituent. Model calculations of Ethresh(l,D) based on changing constituent blood composition during heating with milliseconds lasers were found to correlate with experimental results. Conclusions: For laser treatment of HVSL it appears thatl is of secondary importance and that the choice of tp is a more important factor. Lasers Surg. Med. 36:281–288, 2005. 2005 Wiley-Liss, Inc.

The physical basis for optimization of wavelength, pulse duration, and cooling for laser-induced selective photothermolysis of hair follicles in human skin is discussed. The results indicate that the most important optimization parameter is the cooling efficiency of the technique utilized for epidermal protection. The optical penetration is approximately the same for lasers at 694, 755, and 800 nm. The penetration of radiation from Nd:yttrium-aluminum-garnet lasers at 1064 nm is, however, somewhat larger. Photothermal damage to the follicle is shown to be almost independent of laser pulse duration up to 100 ms. The results reveal that epidermal cooling by a 30-80-ms-long cryogen spurt immediately before laser exposure is the only efficient technique for laser pulse durations less than 10 ms. For longer pulse durations in the 30-100 ms range, protection can be done efficiently by skin cooling during laser exposure. For laser pulses of 100 ms, an extended precooling period, e.g., by bringing a cold object into good thermal contact with the skin for about 1 s, can be of value. Thermal quenching of laser induced epidermal temperature rise after pulsed exposure can most efficiently be done with a 20 ms cryogen spurt applied immediately after irradiation.

Treatment of port wine stains (PWS) by photothermolysis can be improved by optimizing laser parameters. We have studied the all-important role of wavelength (lambda) by performing pulsed laser photothermolysis in the vasculature of the chick chorioallantoic membrane (CAM) assay.The CAM contains an extensive microvascular network ranging from capillaries with diameter D20 microm to blood vessels of D approximately 120 microm. The CAM assay enables observation and real-time video documentation of blood flow in pre-capillary arterioles (A) and post-capillary venules (V). The ScleroPlus trade mark laser (Candela Corp., Wayland, MA) has a smooth output over its fixed 1.5 ms pulse duration and allows the operator to vary several treatment parameters such as wavelength, spot size, and energy. Blood vessels in the CAM were irradiated at two clinically relevant wavelengths, lambda = 587 or 597 nm, constant spot size (7 mm), and at different exposures (E = 5-12 J/cm(2)). Threshold exposure (E(th)) (at which non-reversible damage occurred) were 5 J/cm(2) at 587 nm and 8 J/cm(2) at 597 nm. Mathematical modeling was developed to interpret initial (within 30 seconds) injury of arterioles and venules at both wavelengths as a function of D when varying E.Vessel injury was graded off-line from videotapes. For all combinations of lambda and E, measurable injury was evident within 30 seconds of irradiation and maximal damage was reached in less than 10 minutes. Vessel damage was found to depend strongly on lambda. Damage decreased with increasing vessel size. For all D, damage of arterioles was greater than for corresponding venules.Selection of the correct wavelength is crucial for successful laser therapy of hypervascular lesions and, ideally, should be based on knowledge of vessel diameters for a specific PWS lesion and of optical penetration depths in blood. As a general statement, smaller blood vessels (D = 10-60 microm) should be treated using shorter wavelengths such as 585 nm. To ensure deposition of sufficient laser energy, irradiation at 585 nm, characterized by lower optical penetration depth in blood, may be preferable for PWS therapy.

Most dermatologic laser procedures must consider epidermal melanin, as it is a broadband optical absorber which affects subsurface fluence, effectively limiting the amount of light reaching the dermis and targeted chromophores. An accurate method for quantifying epidermal melanin content would aid clinicians in determining proper light dosage for therapeutic laser procedures. While epidermal melanin content has been quantified non-invasively using optical methods, there is currently no way to determine the melanin distribution in the epidermis. We have developed a photoacoustic probe that uses a Q-switched, frequency doubled Nd:YAG laser operating at 532nm to generate acoustic pulses in skin in vivo . The probe contained a piezoelectric element that detected photoacoustic waves which were then analyzed for epidermal melanin content, using a photoacoustic melanin index (PAMI). We tested 15 human subjects with skin types I--VI using the photoacoustic probe. We also present photoacoustic data for a human subject with vitiligo. Photoacoustic measurement showed melanin in the vitiligo subject was almost completely absent.

Background and Objectives The aim was to study hair removal efficacy, and possible side effects of two commercially available long pulsed diode lasers. The radiant exposure was selected to a value of 35 J/cm2, which is frequently used in the clinic in accordance with manufacturer's recommendations. Study Design/Materials and Methods A prospective clinical study was performed on twenty-nine patients with hair color ranging from light brown to black on the upper lip. One half of the upper lip was randomly selected for treatment with the MedioStar® laser; the contralateral half of the lip was treated with the LightSheer® laser. Three treatments were performed at 6–8 week intervals. Percent hair reduction and acute- and long-term side effects were evaluated after treatment. Results The average hair reductions 6 months after the first treatment were 49% with the MedioStar® laser and 48% with the LightSheer® laser. No scarring or pigmentary change of the skin was observed after any of the treatments with either laser. However, differences in acute side effects such as degree of erythema and burned hairs were observed. Conclusions No statistically significant differences in hair removal efficacy were observed. These results agree with mathematical modeling, which also offers a method to estimate hair removal efficacy and adverse effects for a range of hair characteristics and laser parameters. Lasers Surg. Med. 32:399–404, 2003. © 2003 Wiley-Liss, Inc.

The measurement of the propagation characteristics of Diffuse Photon-Density Waves (DPDW) is a viable path todetermine the optical properties of tissue, i. e. the absorption and the reduced scattering coefficient. The techniqueallows to take measurements from bulk tissue, either by interstitial placement (infinite medium measurement) orsuperficial placement (semi-infinite medium measurement) of the source and detection fibers. Treatment of thetissue prior to measurement is unnecessary, such that changes to the structure of the tissue, and thus the opticalproperties, can be avoided. The optical properties can then be recovered by application of a diffusion model. Whenusing a semi-infinite medium model, non-invasive in vivo measurements are feasible. While the theory is well established and verified by phantom measurements, the small amount of published data for biological tissue acquired by DPDW measurements suggests that there are still open practical problems, both concerning the measurementtechnique and the application of the diffusion model. In this study, we investigate the optimal choice of modulationfrequencies for extracting a maximum amount of information on the scattering and absorption properties, examinedifferent measurement setups, analyze how amplitude and phase data should be combined and compare the qualityof infinite and semi-infinite medium measurements. The considerations are supported by experimental data, basedon measurements from chicken and turkey breast muscle with modulation frequencies of up to 0.4 GHz.Keywords: diffuse photon-density waves, diffusion theory, modulation frequency, optical properties, chicken breastmuscle, turkey breast muscle

The presently most promising treatment modality for port wine stains is selective photothermolysis. This technique is based on exposure of the lesion to yellow laser light of high energy density and long pulse-length, typically 5 - 10 J/cm 2 and 0.5 ms, respectively. Although promising clinical results have been reported, only a small percentage of the patients obtains full fading of their lesions. This might in part be due to the fact that most clinicians treat port wine stains with rather standardized settings of the laser parameters. However, clinical response can, hopefully, be improved if these setting are adjusted to each individual lesion. This paper gives a brief discussion of the importance of parameters such as depth, diameter and vessel wall thickness, together with a presentation of non-invasive methods for determination of these values.

at radiant exposures as low as

Pulsed dye lasers permit effective treatment of port-wine stains without a significant risk of complications. However, epidermal damage manifested by weeping or crusting of the treated area have been reported in 48-83% of patients, and transient hyperpigmentation after treatment is observed in 10-57%. Theoretically, the epidermis can be protected from thermal damage with the use of the concept of selective epidermal cooling.This study examined the clinical effects of rapid cooling of the epidermis with a liquid refrigerant R-134a (boiling point - 26.5 double daggerC) during pulsed dye laser therapy. In 23 patients with port-wine stains, a 50-ms-long cooling pulse delivered immediately prior to laser irradiation with a fluence of 6.0 J cm(-2) significantly reduced the pain, and shortened the period with purpura without compromising the clinical blanching. Cooling periods longer than 60 ms, as well as additional cooling pulses immediately after laser exposure, reduced the blanching in areas irradiated with 6.0 J cm(-2).Post-treatment hyperpigmentation was not prevented with dynamic cooling.

The treatment of port wine stains (PWSs) using a flashlamp-pumped pulsed dye laser is often performed using virtually identical irradiation parameters. Although encouraging clinical results have been reported, we propose that lasers will only reach their full potential provided treatment parameters match individual PWS anatomy and physiology. The purpose of this paper is to review the progress made on the technical development and clinical implementation of (i) infrared tomography (IRT), optical reflectance spectroscopy (ORS) and optical low-coherence reflectometry (OLCR) to obtain in vivo diagnostic data on individual PWS anatomy and physiology and (ii) models of light and heat propagation, predicting irreversible vascular injury in human skin, to select optimal laser wavelength, pulse duration, spot size and radiant exposure for complete PWS blanching in the fewest possible treatment sessions. Although non-invasive optical sensing techniques may provide significant diagnostic data, development of a realistic model will require a better understanding of relevant mechanisms for irreversible vascular injury.

Laser tweezers may act as optical force transducers. We report on the determination of intrinsic motility forces of human spermatozoa by employing an 800 nm optical trap. The cellular forces were calculated from calibrated trapping forces. The determination of trapping forces based on a hydrodynamic model for ellipsoidal specimens, the measurement of the minimum laser power required to confine a single cell in the trap, and the calculation of viscus forces during the movement of optically trapped sperm heads through a laminar fluid. A mean motility force of 44 plus or minus 24 pN was calculated for spermatozoa of healthy donors.

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 optimal treatment of port-wine stains is laser-induced selective photothermolysis. Lesion color and location and the age of the patient are reported to influence the therapeutic outcome. This study was initiated to analyze the outcome not only by the clinical response of lightening, but also in terms of photothermally induced necrosis to the vessel wall. Punch biopsy specimens were taken from 51 patients before treatment. Post-treatment biopsies were taken after exposure to a pulsed dye laser (585-nm wavelength, 0.45-ms pulse length) with an irradiant fluence of 6.5 J/cm2. Vessel diameter, depth, and wall thickness were measured in all histologic slides. The viability of the vessel walls was evaluated using an enzyme histochemical method. Port-wine stains with good blanching had significantly more superficially located vessels than the moderate and poor responders (p0.000). The moderate and good responding lesions consisted of moderate-sized vessels with diameters of 38 +/- 17 micrometers and 38 +/- 19 micrometers (mean +/- SD), respectively. The lesions showing poor blanching had significantly smaller vessels, with a diameter of 19 +/- 6.5 micrometers0.000). Analyses of the post-treatment specimens showed that coagulated vessels were superficially located and of moderate size, whereas the viable vessels were small with a median diameter of 14 micrometers. The probability of coagulation correlated with the thickness of the vessel wall. These data indicate that the therapeutic outcome of port-wine stains can be improved by using the lesional vessel parameters to select the optimal laser wavelength, pulse duration, and dose.

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.

LETTERS TO THE EDITOR Further Investigation of Pigmentary Changes After Alexandrite Laser Hair Removal in Conjunction With Cryogen Spray Cooling To the Editor: We reviewed ‘‘Pigmentary Changes After Alexandrite Laser Hair Removal’’ by Drs. Weisberg and Green- baum with great interest and believe this article to be important in helping to optimize the safety and efficacy of laser-assisted hair removal in conjunction with cryogen spray cooling (CSC). 1 Over the last year, several similar cases of skin dyspigmentation after laser-assisted hair removal in combination with CSC have come to our attention. Clinicians have hypothesized that the damage was secondary to cryo-injury. 2 To determine the validity of this hypothesis, we performed a series of experiments using the RAFT tissue model of human skin in which specimens were exposed to cryogen spurt durations of 10 to 500 ms. 3 We demonstrated that cryogen spurts of up to 80 ms do not result in major epidermal injury and thus are not likely to cause skin dyspigmentation. Moreover, extensive clinical use of CSC with exposure of human skin to cryogen spurt durations of 100 ms or more has not resulted in cryo-injury. 4–6 Drs. Weisberg and Greenbaum speculate that ‘‘super cooling’’ of the distance gauge may be the cause of skin dyspigmentation. We consider this an unlikely expla- nation of injury because distance gauges are generally made from Teflon, which has very low thermal conductivity. To demonstrate that a cooled distance gauge is an unlikely cause of injury, we purged the cryogen for 1 minute without firing the laser, resulting in considerable frost build up on the gauge, which was then placed firmly against a volunteer’s skin for 10 seconds. No discomfort was noted, and no erythema or discoloration occurred immediately or at follow-up over several weeks. We believe the skin dyspigmentation occasionally observed after laser-assisted hair removal in combina- tion with CSC is not cryo-injury, but rather laser- induced thermal injury. Currently available laser devices incorporate epidermal cooling to improve the margin of safety by increasing the threshold for epidermal damage, which allows the use of higher fluences, permits treatment of darker skin types, and decreases patient discomfort. However, to be effective and safe, the cooling medium must completely cover the skin surface before laser irradiation. When epidermal protection is incomplete, thermal injury is likely to result, particularly during the use of higher fluences in patients with darker skin types. In a recent publication, 7 we used thermal-sensitive test paper to compare cryogen coverage with laser spot diameter. In the cases presented by Drs. Weisberg and Greenbaum, a 50-ms cryogen spurt was used to cover an 18-mm diameter spot. We determined that a 50-ms spurt, delivered by a GentleLASE (Candela, Wayland, MA) nozzle similar to that used by Drs. Weisberg and Greenbaum, created a cryogen coverage area of 18 mm.As this is the exact diameter of the laser- irradiated spot, epidermal protection is complete only when the handpiece is held perpendicular to the skin surface. If the handpiece is angled 61 or more from perpendicular normal, incomplete cryogen coverage of the laser spot occurs and a crescent-shaped burn can be observed (Figure 1). We have also noted a similar effect if the cryogen nozzle is misaligned in the handpiece, which may occur with moving of the laser from room to room or between office locations. As a result of the previously described studies, we have three recommendations to mitigate or eliminate the type of adverse effects reported by Drs. Weisberg, Greenbaum, and others. First, when large (15 or 18 mm) spot sizes are used, selection of longer spurt durations will ensure complete cryogen coverage of the irradiated skin surface. Second, cryogen coverage can be quickly confirmed before each procedure or after changes of cooling/laser parameters by firing the beam onto a porous surface such as ordinary cardboard. If thermal injury is noted when the handpiece is held perpendicular and adequate cryogen spurt duration has been chosen, the spray nozzle may be misaligned and require adjustment. Finally, care should be taken to hold the handpiece perpendicular to the skin surface throughout the entire procedure, as indicated in the manufacturer’s guidelines. This may require special attention, particu- larly during treatment of curved anatomic surfaces. We would like to thank Drs. Weisberg and Green- baum for their observations and the educational opportunity provided. Recognition of this potential Figure 1. Burn patterns created on cardboard by an Alexandrite laser in conjunction with CSC (18-mm spot size; 20 J/cm 2 ; 50-ms cooling). (A) Even coverage is noted when the handpiece is held perpendicular to the skin. A progressively more prominent crescent shaped burn pattern was noted when the handpiece was angled at 61 (B) and then 121 (C). The crescent-shaped burn occurred because with angling of the handpiece, the laser spot was not completely covered by the protective cryogen spurt. r 2004 by the American Society for Dermatologic Surgery, Inc. Published by Blackwell Publishing, Inc. ISSN: 1076-0512/04/$15.00/0 Dermatol Surg 2004;30:581–582

The successful treatment of port wine stain (PWS) patients undergoing laser therapy is based on selective thermal coagulation of blood vessels without damaging the normal overlying epidermis. Cryogen spray cooling of skin may offer an effective method for minimizing epidermal thermal injury. Inasmuch as the density of melanosomes and depth of PWS blood vessels can vary considerably, an optimum cooling strategy is required on an individual patient basis. The authors present a theoretical study of the thermal response of various pigmented PWS lesions to spray cooling in conjunction with flashlamp-pumped pulsed dye laser irradiation (585 nm). Results of the authors' model indicate that precooling of skin using tetrafluoroethane as the cryogen spray is sufficient to eliminate epidermal thermal injury when using incident fluences less than 10 J cm -2 and 8 J cm-2 on patients with intermediate and high epidermal melanin content, respectively. Cryogens that have lower boiling points than tetrafluoroethane may allow successful treatment when using fluences equal to or greater than those indicated.

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

The rationale for the use of a new modality such as laser-induced hyperthermia in the treatment of human neoplasm is based on a broad spectrum of research. The general research on hyperthermia has been conducted over a centennial, whereas the work on laser-induced hyperthermia has been carried out over the last decade.

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.

Individual blood vessels in the chick chorioallantoic membrane (CAM) were selectively coagulated through photothermolysis, using pulsed laser irradiation at 585 nm. Pulse durations were chosen to be 0.45 ms and 10 ms, which correspond to the thermal relaxation times in blood vessels of 30 micrometers and 150 micrometers diameter, respectively. The dose vs diameter (D vs d) relationship for coagulation was calculated for the two pulse shapes. The energy deposited in a cylindrical absorber of diameter d by an optical field, incident perpendicular to the vessel, was expressed analytically and compared with the energy required to coagulate a blood vessel of the same lumen diameter. When thermal diffusion is incorporated into the model, our findings can be accounted for quantitatively. This information will be of use for improving the laser treatment of port wine stains and other vasculopathies.

Optical techniques represent a valuable tool for analysis of turbid media. Recent development has emphasized dynamic measurements where either ultrashort laser pulses or high frequency amplitude modulated laser light are launched into the medium. The properties of the transmitted light range from quasi-coherent in media with limited scattering to the almost randomized incoherent behavior in strongly turbid media. The present discussion considers the influence of a boundary between a heavily scattering medium with an almost isotropic diffuse light distribution and a non-scattering medium. This case can be approximated in terms of well established solutions of the diffusion equation. It is further demonstrated that the somewhat composite mathematical expressions can be interpreted in a very simple, intuitive manner. This type of approximation is, of course, of limited validity in the surface layer itself. However, the simplicity of this approximation might make it a valuable tool for several applications.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The application of pulsed photothermal radiometry (PPTR) diagnostics to characterize port wine stain (PWS) lesions is discussed. Influence of epidermal absorbance and PWS depth on the PPTR signal is analyzed using an in-vitro model of PWS skin consisting of multilayered collagen films. An instrument is constructed and used for patient and animal model PPTR measurements. When an infrared fiber is incorporated, the instrumentation facilitates convenient skin-site accessibility. Modulation of the PPTR signal and homodyne detection substantially improve the system signal-to-noise ratio over previous methods. Given the measured PPTR signal, an algorithm computes the initial temperature distribution in the PWS skin immediately after the laser pulse. The use and limitations of the algorithm are presented and discussed.

The application of pulsed photothermal radiometry (PPTR) diagnostics to characterize port wine stain (PWS) lesions is discussed. A PPTR signal of a PWS in response to pulsed laser exposure is shown to consist of an initial `T-jump' due to epidermal melanin absorption and a `delayed thermal wave' resulting from laser generated heat in subsurface blood vessels diffusing to the skin surface. A prototype PPTR instrument incorporating an infrared fiber is constructed which facilitates convenient skin-site accessibility. Laser heating of the infrared collection optics results in an artifactual signal which overestimates the initial `T-jump.' Magnitude of the error is measured and a method to eliminate it is suggested.

The response of tissue to laser radiation spans the gauntlet from biostimulation at irradiance levels of mW to the violent disruptions of tissue with short pulses that have MW peak irradiances. The end result of laser interaction with tissue is governed by energy Deposition that depends upon laser parameters and tissue properties. In concept, PDT requires a laser wavelength that matches an absorption peak of the photosensitizer and a penetration depth to reach all of the targeted tissue. Dosimetry will depend upon the needed fluence rate 4(z) of the light at the targeted depth. Given the optical properties of the tissue, various methods of solving the transport equation can be used to calculate fluence rate [W1m2] as a function of depth. Since most wavelengths of interest for PDT are in the red and near IR, scattering dominates absorption; and the fluence rate just below the surface of tissue can be much larger than the irradiance, EO [W/m2].

The chick chorioallantoic membrane (CAM) model was used to study vascular effects of photodynamic therapy (PDT) and hyperthermia (HPT) and the synergism of these modalities. The CAM is a convenient medium for monitoring the modifications of the vasculature. It is possible to view the CAM and to examine structural changes of individual blood vessels in real time. Moreover, the CAM is a closed system which lends itself to mathematical modeling of the temporal and spatial temperature profile and in which HPT can be performed quantitatively and to a selected depth, using different lasers. A porphyrin-type photosensitizer solution was applied to areas of the CAM, defined by teflon O-rings placed on the surface. Uptake dynamics of the sensitizer into the CAM was determined by analyzing its fluorescence in vivo. The CAM area was irradiated with a dual-wavelength laser system composed of a dye laser at 644 nm (to induce PDT) and a CO2 laser at 10.6 microns (to bring about HPT). Damage to the CAM vasculature, due to combined PDT+HPT, was compared to the outcome of the separate modalities, and a synergistic effect of about 40% was observed.

Objective quantification of epidermal melanin concentration (EMC) should be useful in laser dermatology to determine the individual maximum safe radiant exposure (IMSRE). We propose a single-wavelength remittance measurement at 390 nm as an alternative optical method to determine EMC and IMSRE. Remittance spectra (360 to 740 nm), melanin index (MI) measurements and the transient radiometric temperature increase, DeltaT(t), upon skin irradiation with an Alexandrite laser (755 nm, 3-ms pulse duration, 6 Jcm(2)) were measured on 749 skin spots (arm and calf) on 23 volunteers (skin phototypes I to IV). Due to the shallow penetration depth and independence of blood oxygen saturation (isosbestic point), remittance at 390 nm appears to provide better estimates for EMC and IMSRE than MI.

Two methods for clinical optical light dosimetry are developed. In the first method, which is invasive, a fluorescent probe attached to an optical fiber is inserted by means of a thin hypodermic needle and measures light transmitted through the cheek as a function of the penetration depth. In the second noninvasive method, the diffusely reflected light intensity, from a small illuminated spot on the surface of the tissue to be investigated, is measured as a function of the radial distance along the surface. Preliminary results with both methods are presented. Simulations of the second measurements, which allow for a simplified extraction procedure of the relevant optical data from such measurements, are also shown.

It is hard to imagine that a narrow, one-way, coherent, moving, amplified beam of light fired by excited atoms is powerful enough to slice through steel. In 1917, Albert Einstein speculated that under certain conditions atoms could absorb light and be stimulated to shed their borrowed energy. Charles Townes coined the term laser (light amplification by stimulated emission of radiation) in 1951. Theodore Maiman investigated the glare of a flash lamp in a rod of synthetic ruby, creating the first human-made laser in 1960. The laser involves exciting atoms and passing them through a medium such as crystal, gas or liquid. As the cascade of photon energy sweeps through the medium, bouncing off mirrors, it is reflected back and forth, and gains energy to produce a high wattage beam of light. Although lasers are today used by a large variety of professions, one of the most meaningful applications of laser technology has been through its use in medicine. Being faster and less invasive with a high precision, lasers have penetrated into most medical disciplines during the last half century including dermatology, ophthalmology, dentistry, otolaryngology, gastroenterology, urology, gynaecology, cardiology, neurosurgery and orthopaedics. In many ways the laser has revolutionized the diagnosis and treatment of a disease. As a surgical tool the laser is capable of three basic functions. When focused on a point it can cauterize deeply as it cuts, reducing the surgical trauma caused by a knife. It can vaporize the surface of a tissue. Or, through optical fibres, it can permit a doctor to see inside the body. Lasers have also become an indispensable tool in biological applications from high-resolution microscopy to subcellular nanosurgery. Indeed, medical lasers are a prime example of how the movement of an idea can truly change the medical world. This review will survey various applications of lasers in medicine including four major categories: types of lasers, laser-tissue interactions, therapeutics and diagnostics.

Experimental results for the optical properties of ocular tumors in the red to near infrared region from 600-900 nm and at the near infrared wavelength of 1064 nm are presented. The tumor models have been human retinoblastoma heterotransplanted in athyinic mice and B16 melanotic melanoma in athymic mice. The steady state retinal and tumor temperature rise during 1064 nm laser irradiation have been examined in vivo in normal albino and pigmented rabbits eye and in Greene''s melanoma inoculated in the retinachoroidal layers. 2.

Background and Design: The clinical objective in the treatment of a patient with port-wine stain (PWS) undergoing laser therapy is to maximize thermal damage to the PWS, while at the same time minimizing nonspecific injury to the normal overlying epidermis. With dynamic cooling, the epidermis can be cooled selectively. When a cryogen spurt is applied to the skin surface for an appropriately short period of time (on the order of tens of milliseconds), the cooling remains localized in the epidermis, while leaving the temperature of the deeper PWS vessels unchanged. Results: Comparative measurements obtained by a fast infrared imaging detector demonstrated that the surface temperature prior to laser exposure could be reduced by as much as 40°C using the dynamic cooling technique. No skin surface textural changes were noted on PWS test sites cooled with a 20- to 80-millisecond cryogen spurt after flashlamp-pumped pulsed dye laser (FLPPDL) exposure (λ=585 nm; τp=450 microseconds) at the maximum light dosage possible (10 J/cm2). In contrast, epidermal necrosis occurred on the uncooled sites after such exposure. Six months after laser exposure, clinically significant blanching on the cooled sites indicates laser photothermolysis of PWS blood vessels did occur. Conclusions: Our preliminary experiments demonstrate the feasibility of selectively cooling the normal overlying epidermis without affecting the temperature of the deeper PWS vessels. Furthermore, protection of the epidermis from thermal injury, produced by melanin light absorption at clinically relevant wavelengths, can be achieved effectively. An additional advantage of dynamic epidermal cooling is reduction of patient discomfort associated with FLPPDL therapy. Further studies are under way to determine an optimum strategy for applying this dynamic cooling technique during pulsed laser treatment of patients with PWS and others with selected dermatoses (dermal melanocytic lesions and tattoos). (Arch Dermatol. 1995;131:695-700)