Effect of surface thermal variations during cryogen spray cooling in dermatologic laser therapy (original) (raw)
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Intermittent cryogen spray cooling for optimal heat extraction during dermatologic laser treatment
Physics in Medicine and Biology, 2002
Fast heat extraction is critically important to obtain the maximal benefit of cryogen spray cooling (CSC) during laser therapy of shallow skin lesions, such as port wine stain birthmarks. However, a film of liquid cryogen can build up on the skin surface, impairing heat transfer due to the relatively low thermal conductivity and higher temperature of the film as compared to the impinging spray droplets. In an attempt to optimize the cryogen mass flux, while minimally affecting other spray characteristics, we apply a series of 10 ms spurts with variable duty cycles. Heat extraction dynamics during such intermittent cryogen sprays were measured using a custom-made metal-disc detector. The highest cooling rates were observed at moderate duty cycle levels. This confirms the presence, and offers a practical way to eliminate the adverse effect of liquid cryogen build-up on the sprayed surface. On the other hand, lower duty cycles allow a substantial reduction in the average rate of heat extraction, enabling less aggressive and more efficient CSC for treatment of deeper targets, such as hair follicles.
Cooling efficiency of cryogen spray during laser therapy of skin
Lasers in surgery and medicine, 2003
Cryogen spray cooling (CSC) is used extensively for epidermal protection during laser-induced photothermolysis of port wine stains and other vascular skin lesions. The efficacy of CSC depends critically on the heat transfer coefficient (H) at the skin surface for which, however, no reliable values exist. Reported values for H, based on tissue phantoms, vary from 1,600 to 60,000 W/m(2) K.
Lasers in Surgery and Medicine, 2006
Background and Objectives: Although cryogen spray cooling (CSC) in conjunction with laser therapy has become the clinical standard for treatment of port wine stain (PWS) birthmarks, the current approach does not produce complete lesion blanching in the vast majority of patients. The objectives of this study are to: (1) experimentally determine the dynamic CSC heat flux when a skin phantom is preheated, and (2) numerically study the feasibility of using skin preheating prior to CSC to improve PWS laser therapeutic outcome. Study Design/Materials and Methods: A fast-response thin-foil thermocouple was used to measure the surface temperature and thus heat flux of an epoxy skin phantom during CSC. Using the heat flux as a boundary condition, PWS laser therapy was simulated with finite element heat diffusion and Monte Carlo light distribution models. Epidermal and PWS blood vessel thermal damage were calculated with an Arrhenius-type kinetic model. Results: Experimental results show that the skin phantom surface can be cooled to a similar minimum temperature regardless of the initial temperature. Numerical simulation indicates that upon laser irradiation, the epidermal temperature increase is virtually unaffected by preheating, while higher PWS blood vessel temperatures can be achieved. Based on the damage criterion we assumed, the depth and maximum diameter of PWS vessels that can be destroyed irreversibly with skin preheating are greater than those without. Conclusions: Skin preheating prior to CSC can maintain epidermal cooling while increasing PWS blood vessel temperature before laser irradiation. Numerical models have been developed to show that patients may benefit from the skin preheating approach, depending on PWS vessel diameter and depth.
IEEE Journal of Selected Topics in Quantum Electronics, 1999
In many port wine stain (PWS) patients, successful clearing is not achieved even after multiple laser treatments because of inadequate heat generation within the targeted blood vessels. Use of higher radiant exposures has been suggested to improve lesion clearing, but risk of epidermal injury due to nonspecific absorption by melanin increases. It has been demonstrated that cryogen spray cooling (CSC) can protect the epidermis from nonspecific thermal injury during laser treatment of PWS. Inasmuch as epidermal melanin concentration and blood vessel depth vary among patients, evaluation of internal skin temperatures in response to CSC is essential for further development and optimization of treatment parameters on an individual patient basis. We present internal temperature measurements in an epoxy resin phantom in response to CSC and use the results in conjunction with a mathematical model to predict the temperature distribution within human skin for various cooling parameters. Measurements on the epoxy resin phantom show that cryogen film temperature is well below the cryogen boiling point, but a poor thermal contact exists at the cryogenphantom interface. Based on phantom measurements and model predictions, internal skin temperature reduction remains confined to the upper 400 m for spurt durations as long as 200 ms. At the end of a 100 ms spurt, our results show a 31 C temperature reduction at the surface, 12 C at a depth of 100 m, and 4 C at a depth of 200 m in human skin. Analysis of estimated temperature distributions in response to CSC and temperature profiles obtained by pulsed photothermal radiometry indicates that a significant protective effect is achieved at the surface of laser irradiated PWS skin. Protection of the epidermal basal layer, however, poses a greater challenge when high radiant exposures are used.
Methodology for Characterizing Heat Removal Mechanism in Human Skin During Cryogen Spray Cooling
Annals of Biomedical Engineering, 2000
Cryogen spray cooling ͑CSC͒ reduces epidermal damage during laser treatment of various dermatoses. The goal of this study was to determine the heat removal mechanism in skin and quantify the amount in response to CSC. Thermocouples were imbedded in four model substrates with a range of thermal diffusivities, greater than three orders of magnitude in difference, to measure the temperature profiles in response to CSC and sapphire contact cooling, which removes heat completely by conduction. An algorithm solving an inverse heat conduction problem was subsequently used to quantify the amount of heat removal from the substrates using the measured temperatures. The interface thermal conductance and internal temperatures within the substrates were computed by a finite difference algorithm that solved the heat conduction equation. Results verify a marked increase in heat removal and interface thermal conductance with increasing thermal diffusivity. By estimation from the model substrate results, heat removal and interface thermal conductance values for skin were obtained. Data demonstrate that during CSC, evaporation is the dominant heat transfer mechanism in materials with higher thermal diffusivities; however, conductive cooling dominates in substrates with lower thermal diffusivities such as skin.
Physics in Medicine and Biology, 1995
The successful treatment of port wine stain (PWS) patients undergoing laser therapy is based on selective thermal coagulation ofblood 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 densiry of melanosomes and depth of PWS blood vessels can vary considerably, an optimum cooling strategy is required on an individual patient basis. We present a theoretical study of the thermal response of various pigmented PWS lesions to spray cooling in canjunction with flashlamppumped pulsed dye laser in;ldiation (585 nm). Results of our model indicate that precooling of skin using tetrafluoroethane as the cryogen spray is sufficient to eliminate epidermal thermal injury when using incident Ruences less than 10 J cm-' and 8 J c N 2 on patients with intermediate and high epidermal melanin content, respectively. Cryogens that have lower boiling points than temfluoroethane may allow successful treatment when using Ruences equal to or greater than those indicated.
Lasers in Surgery and Medicine, 2002
Background and Objectives: Cryogen spray cooling (CSC) is used to minimize the risk of epidermal damage during laser treatment of port wine stain (PWS) birthmarks. Unfortunately, CSC may not provide the necessary protection for patients with high concentrations of epidermal melanin. The objectives of this study are to: (1) provide a definition of cooling efficiency (h) based on the amount of heat removed per unit area of skin for a given cooling time; (2) using this definition, establish the h of previously reported spray nozzles; (3) identify the maximum benefit expected in PWS laser therapy based solely on improvement of h; and (4) study the feasibility of using multipleintermittent cryogen spurts and laser pulses to improve PWS laser therapy. Study Design/Materials and Methods: A theoretical definition to quantify h is introduced. Subsequently, finite difference heat diffusion and Monte Carlo light distribution models are used to study the spatial and temporal temperature distributions in PWS skin considering: (1) the current approach to PWS laser therapy consisting of a single cryogen spurt followed by a single pulsed dye laser exposure (SCS-SLP approach); and (2) multiple cryogen spurts and laser pulses (MCS-MLP approach). At the same time, an Arrhenius-type kinetic model is used to compute the epidermal and PWS thermal damages (O E and O PWS , respectively) for a high epidermal melanin concentration (20%), corresponding to skin types V-VI. Results: The h corresponding to a wide range of heat transfer coefficients (h) is quantified. For reported CSC nozzle devices h varies from 40 to 98%. Using the SCS-SLP approach, it is shown that even h ¼ 100% cannot prevent excessive O E for a skin types V-VI. In contrast, the MCS-MLP approach provides adequate epidermal protection while permitting PWS photocoagulation for the same skin types. Conclusions: The new proposed definition allows to compute the cooling efficiency of CSC nozzle devices. Computer models have been developed and used to show that the SCS-SLP approach will not provide adequate epidermal protection for darker skin patients (skin types V-VI), even for h ¼ 100%. In contrast, the MCS-MLP approach may be a viable solution to improve PWS laser therapy for darker skin patients.
Storage and Retrieval for Image and Video Databases, 2001
Cryogen spray cooling (CSC) is used to minimize the risk of epidermal damage in various laser dermatological procedures such as treatment of port wine stain birthmarks and hair removal. However, the spray characteristics and combination of CSC and heating (laser) to obtain optimal treatments have not yet been determined. The distance between the nozzle tip and the skin surface for
Physics in Medicine and Biology, 2004
High speed video imaging and an inverse heat conduction problem algorithm were used to observe and measure the effect of the angle between the nozzle and surface of a skin phantom on: (a) surface temperature; (b) heat flux q; and (c) overall heat extraction Q during cryogen spray cooling (CSC). A skin phantom containing a fast-response temperature sensor was sprayed with 50 ms cryogen spurts from a commercial nozzle placed 30 mm from the surface. The nozzle was systematically positioned at angles ranging from 5 • to 90 • (perpendicular) with respect to the phantom surface. It is shown that angles as low as 15 • have an insignificant impact on the surface temperature, q and Q. Only exaggerated angles of 5 • show up to 10% lower q and 30% lower Q with respect to the maximal values measured when nozzles are aimed perpendicularly. This study proves that the slight angle that many commercial nozzles have does not affect significantly the CSC efficiency. Aguilar G, Diaz S H, Lavernia E J and Nelson J S 2002 Cryogen spray cooling efficiency: improvement of port wine stain laser therapy through multiple-intermittent cryogen spurts and laser pulses Lasers Surg. Med. 31 27-35 Aguilar G, Majaron B, Karapetian E, Lavernia E J and Nelson J S 2003a Experimental study of cryogen spray properties for application in dermatologic laser surgery IEEE Trans. Biomed. Eng. 50 863-9 Aguilar G, Majaron B, Pope K, Svaasand L O, Lavernia E J and Nelson J S 2001a Influence of nozzle-to-skin distance in cryogen spray cooling for dermatologic laser surgery Lasers Surg. Med. 28 113-20 Aguilar G, Verkruysse W, Majaron B, Svaasand L O, Lavernia E J and Nelson J S 2001b Measurement of heat flux and heat transfer coefficient during continuous cryogen spray cooling for laser dermatologic surgery IEEE J. Sel. Top. Quantum Electron. 7 1013-21 Aguilar G, Wang G X and Nelson J S 2003b Dynamic behavior of cryogen spray cooling: effects of spurt duration and spray distance Lasers Surg. Med. 32 152-9 Aguilar G, Wang G X and Nelson J S 2003c Effect of spurt duration on the heat transfer dynamics during cryogen spray cooling Phys. Med. Biol. 48 2169-81 S 1999 Cryogen spray cooling and higher fluence pulsed dye laser treatment improve port-wine stain clearance while minimizing epidermal damage Dermatol. Surg. 25 767-72 Dai T, Pikkula B M, Tunnell J W, Chang D W and Anvari B 2003 Thermal response of human skin epidermis to 595-nm laser irradiation at high incident dosages and long pulse durations in conjunction with cryogen spray cooling: an ex-vivo study Cryogen spray cooling during Nd:YAG laser treatment of hemangiomas. A preliminary animal model study Dermatol. Surg. 23 635-41 Karl A and Frohn A 2000 Experimental investigation of interaction processes between droplets and hot walls Phys. Fluids 12 785-96 Majaron B, Kimel S, Verkruysse W, Aguilar G, Pope R, Svaasand L O, Lavernia E J and Nelson J S 2001 Cryogen spray cooling in laser dermatology: effects of ambient humidity and frost formation Lasers Surg. Med. 28 469-76 Nelson J S, Milner T E, Anvari B, Tanenbaum B S, Kimel S, Svaasand L O and Jacques S L 1995 Dynamic epidermal cooling during pulsed laser treatment of port-wine stain. A new methodology with preliminary clinical evaluation Arch. Dermatol. 131 695-700 Ortiz L and Gonzalez J E 1999 Experiments on steady-state high heat fluxes using spray cooling Exp. Heat Transfer 12 215-33 Pikkula B M, Torres J H, Tunnell J W and Anvari B 2001 Cryogen spray cooling: effects of droplet size and spray density on heat removal Lasers Surg. Med. 28 103-12 Torres J H, Nelson J S, Tanenbaum B S, Milner T E, Goodman D M and Anvari B 1999 Estimation of internal skin temperatures in response to cryogen spray cooling: implications for laser therapy of port wine stains IEEE J. Sel. Top. Quantum Electron. 5 1058-66 Torres J H, Tunnell J W, Pikkula B M and Anvari B 2001 An analysis of heat removal during cryogen spray cooling and effects of simultaneous airflow application Lasers Surg. Med. 28 477-86 Tunnell J W, Torres J H and Anvari B 2002 Methodology for estimation of time-dependent surface heat flux due to cryogen spray cooling Ann. Biomed. Eng. 30 19-33 Verkruysse W, Majaron B, Aguilar G, Svaasand L O and Nelson J S 2000a Dynamics of cryogen deposition relative to heat extraction rate during cryogen spray cooling Proc. SPIE 3907 37-48 Verkruysse W, Majaron B, Tanenbaum B S and Nelson J S 2000b Optimal cryogen spray cooling parameters for pulsed laser treatment of port wine stains Lasers Surg. Med. 27 165-70 Vu H, Aguilar G and Nelson J S 2004 Passive mass deposition control of cryogen sprays through the use of wire meshes Lasers Surg. Med. 34 329-34
Optimal cryogen spray cooling parameters for pulsed laser treatment of port wine stains
Lasers in Surgery and Medicine, 2000
In dermatologic laser therapy, cryogen spray cooling (CSC) is a means to protect the epidermis while leaving dermal structures susceptible to thermal damage. The purpose of this study was to determine optimal spurt duration, s , and optimal delay, d , between the cryogen spurt and laser pulse when using CSC in treatment of port wine stain birthmarks.