Intermittent cryogen spray cooling for optimal heat extraction during dermatologic laser treatment (original) (raw)
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Effect of surface thermal variations during cryogen spray cooling in dermatologic laser therapy
Proc. ILASS Americas. …, 2004
Cryogen spray cooling (CSC) is a spatially selective heat transfer technique that provides epidermal protection during laser treatment of selected dermatoses, such as port wine stain (PWS) birthmarks. Most numerical studies of CSC-assisted PWS therapies to date assume constant cooling conditions at the skin surface. In the present study, however, we show that cooling conditions at the skin surface vary significantly both in time and space. The objective of this paper is to assess the effect of thermal variations at the skin surface on the heat extraction process during PWS laser therapy. First, a single temperature sensor systematically recorded temperature changes along the sprayed area of a skin model. Next, a multiple temperature sensor acquired temperature data at four strategic radial locations namely, at the center, middle, perimeter and outside the sprayed area. Finally, recorded temperatures along with an inverse heat conduction problem (IHCP) algorithm were used to study the heat extraction process at the surface. Spatial and dynamic profiles of surface temperatures, heat fluxes, heat transfer coefficients and heat removal are presented. Results show that local and temporal variations of the boundary conditions may have a strong influence on CSC cooling efficiency during dermatologic laser therapy. The study shows that external conditions must be considered and ideally controlled to optimize current laser therapies of selected dermatoses, such as PWS.
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.
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
Sequential cryogen spraying for heat flux control at the skin surface
Proceedings of SPIE - The International Society for Optical Engineering, 2001
Heat transfer rate at the skin-air interface is of critical importance for the benefits of cryogen spray cooling in combination with laser therapy of shallow subsurface skin lesions, such as port -wine stain birthmarks. With some cryogen spray devices, a layer of liquid cryogen builds up on the skin surface during the spurt, which may impair heat transfer across the skin surface due to relatively low thermal conductivity and potentially higher temperature of the liquid cryogen layer as compared to the spray droplets. While the mass flux of cryogen delivery can be adjusted by varying the atomizing nozzle geometry, this may strongly affect other spray properties, such as lateral spread (cone), droplet size, velocity, and temperature distribution. We present here first experiments with sequential cryogen spraying, which may enable accurate mass flux control thro ugh variation of spray duty cycle, while minimally affecting other spray characteristics. The observed increase of cooling rate and efficiency at moderate duty cycle levels supports the above described hypothesis of "isolating" liquid layer, and demonstrates a novel approach to optimization of cryogen spray devices for individual laser dermatological applications.
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
Influence of nozzle-to-skin distance in cryogen spray cooling for dermatologic laser surgery
Lasers in Surgery and Medicine, 2001
Background and ObjectiveCryogen sprays are used for cooling human skin during various laser treatments. Since characteristics of such sprays have not been completely understood, the optimal atomizing nozzle design and operating conditions for cooling human skin remain to be determined.Cryogen sprays are used for cooling human skin during various laser treatments. Since characteristics of such sprays have not been completely understood, the optimal atomizing nozzle design and operating conditions for cooling human skin remain to be determined.Materials and MethodsTwo commercial cryogenic spray nozzles are characterized by imaging the sprays and the resulting areas on a substrate, as well as by measurements of the average spray droplet diameters, velocities, temperatures, and heat transfer coefficients at the cryogen-substrate interface; all as a function of distance from the nozzle tip.Two commercial cryogenic spray nozzles are characterized by imaging the sprays and the resulting areas on a substrate, as well as by measurements of the average spray droplet diameters, velocities, temperatures, and heat transfer coefficients at the cryogen-substrate interface; all as a function of distance from the nozzle tip.ResultsSize of spray cones and sprayed areas vary with distance and nozzle. Average droplet diameter and velocity increase with distance in the vicinity of the nozzle, slowly decreasing after a certain maximum is reached. Spray temperature decreases with distance due to the extraction of latent heat of vaporization. At larger distances, temperature increases due to complete evaporation of spray droplets. These three variables combined determine the heat transfer coefficient, which may also initially increase with distance, but eventually decreases as nozzles are moved far from the target.Size of spray cones and sprayed areas vary with distance and nozzle. Average droplet diameter and velocity increase with distance in the vicinity of the nozzle, slowly decreasing after a certain maximum is reached. Spray temperature decreases with distance due to the extraction of latent heat of vaporization. At larger distances, temperature increases due to complete evaporation of spray droplets. These three variables combined determine the heat transfer coefficient, which may also initially increase with distance, but eventually decreases as nozzles are moved far from the target.ConclusionsSprayed areas and heat extraction efficiencies produced by current commercial nozzles may be significantly modified by varying the distance between the nozzle and the sprayed surface. Lasers Surg. Med. 28:113–120, 2001. © 2001 Wiley-Liss, Inc.Sprayed areas and heat extraction efficiencies produced by current commercial nozzles may be significantly modified by varying the distance between the nozzle and the sprayed surface. Lasers Surg. Med. 28:113–120, 2001. © 2001 Wiley-Liss, Inc.
Experimental Study of Cryogen Spray Properties for Application in Dermatologic Laser Surgery
Biomedical Engineering, 2003
Cryogenic sprays are used for cooling human skin during laser dermatologic surgery. In this paper, six straight-tube nozzles are characterized by photographs of cryogenic spray shapes, as well as measurements of average droplet diameter, velocity, and temperature. A single-droplet evaporation model to predict average spray droplet diameter and temperature is tested using the experimental data presented here. The results show
Influence of cryogen spray cooling parameters on the heat extraction rate from a sprayed surface
SPIE Proceedings, 2002
Cryogen spray cooling is used to prevent epidermal thermal damage during port-wine stain laser therapy, despite the limited understanding of the fluid dynamics, thermodynamics, and heat transfer characteristics of cryogen sprays. In recent studies, it has been suggested that the heat flux through human skin could be increased by changing physical parameters such as nozzle-to-skin distance, nozzle diameter, and/or by depositing cryogen in sequential spurts. These changes affect spray parameters such as droplet diameter, velocity, and spray temperature. Therefore, in order to optimize new nozzle designs, it is necessary to explore the influence that these fundamental spray parameters have on heat extraction. In this paper, various valve/nozzle configurations were characterized. A Phase Doppler Particle Analyzer was used to determine the average diameter, velocity, and droplet concentration of various cryogen sprays. The mass flux delivered by each valve/nozzle configuration was also measured, along with the average spray temperature. A custom-made device consisting of an insulated metallic disk was used to measure the heat extracted by different sprays. The results showed that there are significant differences in the heat extracted by the different valve/nozzle configurations. These variations are proportionally influenced by mass fluxes. Strong correlations were also observed between average droplet velocities and heat extraction. These findings indicate that mass flux has a dominant effect on heat extraction from human skin during cryogen spray cooling. It is also apparent that kinetic and thermal energies are other parameters to be considered when optimizing heat extraction.
IEEE Journal of Selected Topics in Quantum Electronics, 2001
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 (qs) 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 N = 0.7 mm, we found that qs varies from 15 to 130 W/cm2 and h increases nonlinearly from 15000 to 35000 W/m2.K in the explored range of surface temperatures (Ts , from -32 to -7°C). Values of qs obtained with a wider diameter nozzle (dN = 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/m2.K) and almost independent of Ts 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 qs. 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 qs
SPIE Proceedings, 2003
Cryogen spray cooling (CSC) is used to minimize the risk of epidermal damage during laser dermatologic surgery. During CSC, skin surface is cooled by a short spurt of refrigerant R134a with boiling point of-26.2 o C. Since R134a is volatile in open atmospheric conditions, the atomized liquid droplets undergo continuous evaporation as they fly in air, leading to a lost momentum and mass. Therefore, the cooling effect of CSC depends strongly on the spray distance between the nozzle and the skin surface (L). The objective of this study was, therefore, to investigate the effect of L on the dynamic heat transfer of CSC. A skin model system made of poly methyl-methacrylate resin (Plexiglass®) is used to simulate CSC during laser dermatologic surgery. A fast-response temperature measurement sensor is built using thin (20 µm) aluminum foil and placed on top of the plexiglass with a 50 µm bead diameter thermocouple positioned in between. Variation of the surface temperature is then measured under various spray distances. The surface heat flux (q) as well as the heat transfer coefficient (h) between the surface and the cryogen is estimated by solving an inverse heat conduction problem with the measured temperature data as input. The effect of L on surface cooling in CSC is then investigated systematically. Both the estimated q and h show strong dynamic characteristics and are strong functions of the L. Two distinct spray-surface interaction mechanisms are identified within the spray distances studied. For short L (< 30 mm), the spurt droplets impinge on the substrate violently, resulting in a fairly thin cryogen film deposited on the surface. Strong dynamics and high q result in this case, corresponding to a high h as well. Interestingly, h becomes strongly fluctuating and even larger after spurt termination for these cases. For long L (> 30 mm), q is lower and it steadily decreases after spurt termination. The dynamic variation of h in this case is similar to that of q. These results should help in the selection of optimal CSC parameters, which are needed to produce high heat fluxes at the skin surface and thus obtain maximal epidermal protection during various dermatologic laser therapies.