Methodology for Characterizing Heat Removal Mechanism in Human Skin During Cryogen Spray Cooling (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.
A comparative study of human skin thermal response to sapphire contact and cryogen spray cooling
IEEE Transactions on Biomedical Engineering, 1998
Surface cooling, in conjunction with various thermally mediated therapeutic procedures, can provide a means to protect superficial tissues from injury while achieving destruction of deeper targeted structures. We have investigated the thermal response of in-vivo human skin to: 1) contact cooling with a sapphire window (6-12 C); and 2) spray cooling with a freon substitute cryogen [tetrafluoroethane; boiling point 026 C at 1 atmospheric pressure (atm)]. Measurements utilizing infrared radiometry show surface temperature reductions from 30 C to 14-19 C are obtained within approximately 1 s in response to sapphire contact cooling. Surface temperature reductions to values between 5 C and 09 C are obtained in response to 20-100-ms cryogen spurts. Computational results, based on fitting the measured radiometric surface temperature to estimate heat transfer parameters, show: 1) temperature reductions remain localized to approximately 200 m of superficial tissue; and 2) values of heat flux and total energy removed per unit skin surface area at least doubled when using cryogen spray cooling.
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.
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
Lasers in Surgery and Medicine, 2005
Background: Although cryogen spray cooling (CSC) is used to minimize the risk of epidermal damage during laser dermatologic surgery, concern has been expressed that CSC may induce cryo-injury. In order to address this concern, it is necessary to evaluate the effects of prolonged exposure of human skin phantoms (HSP) to CSC. Objective: To measure the minimum surface temperature (T min ) and the time at which it occurs (t Tmin ) as well as determine the time the sprayed HSP surface remains below 08C (sub-zero time, Dt s ) and À268C (residence time, Dt r ) during the application of single (SCS) and multiple (MCS) cryogen spurts. Two initial HSP substrate temperatures were studied, T i : 23 and 708C. Study Design/Materials and Methods: An epoxy-based HSP was constructed to measure T min , t Tmin , Dt s , and Dt r , for 17 spray patterns: 1 SCS with a total cryo-delivery time (Dt c ) of 40 milliseconds; 8 MCS patterns with identical Dt c , but with a total cooling time (Dt total ) varying from 50 to 280 milliseconds; and 8 SCS patterns that matched the Dt total of the MCS patterns. Results: For both T i , our results show that it is possible to distinguish between two different cooling regimes. For Dt total 110 milliseconds, the differences between SCS and MCS patterns with the same Dt total for all variables (T min , t Tmin , Dt s , Dt r ) are negligible. Most importantly, all these variables show a remarkable linear dependence with Dt total . In the interval 110 milliseconds < Dt total < 280 milliseconds, T min and t Tmin are similar for SCS and MCS, while Dt s and Dt r show more pronounced differences between the two spray patterns. In this interval, the values of T min and Dt s for MCS remain invariant and similar to the corresponding values for Dt total ¼ 110 milliseconds. Conclusions: These results suggest that: (1) similar epidermal protection may be attained with SCS and MCS for Dt total 110 milliseconds; and (2) for 110 milliseconds < Dt total 280 milliseconds, MCS help to maintain Dt s similar to that of SCS at Dt total ¼ 100 milliseconds, which may be beneficial to prevent cryo-injury.
Internal temperature measurements in response to cryogen spray cooling of a skin phantom
Lasers in Surgery: Advanced Characterization, Therapeutics, and Systems IX, 1999
Cryogen spray cooling (CSC) can protect the epidermis from non-specific thermal injury during laser treatment of port wine stains and other hypervascular cutaneous malformations. Knowledge of skin internal temperatures in response to CSC is essential for optimization of this technique. We used an epoxy resin compound to construct a skin phantom and measured its internal temperatures in response to cooling with different cryogens at various spurt durations, spraying distances, and ambient humidity levels. The measured temperature distributions during CSC were fitted by a mathematical model based on thermal diffusion theory. For spurt durations up to 100 ms, temperature reduction within the phantom remained confined to the upper 200 tm, and was affected by spraying distance. Depending on the cryogen used, temperature reductions up to 45°C could be measured 20 im below the surface at the end of a 100 ms spurt. However, the cryogen film temperature on the epoxy resin surface was up to 35°C lower, indicating lack ofperfect thermal contact at the cryogen film-phantom interface. Theoretical predictions were within 10% ofmeasured temperatures. Ice formation occurred following termination of the spurt and was influenced by the ambient humidity level.
Radial and temporal variations in surface heat transfer during cryogen spray cooling
Physics in Medicine and Biology - PHYS MED BIOL, 2005
Cryogen spray cooling (CSC) is a heat extraction process that protects the epidermis from thermal damage during dermatologic laser surgery. The objective of the present work is to investigate radial and temporal variations in the heat transferred through the surface of a skin phantom during CSC. A fastresponse thermal sensor is used to measure surface temperatures every 1 mm across a 16 mm diameter of the sprayed surface of the phantom. An analytical expression based on Fourier's law and Duhamel's theorem is used to compute surface heat fluxes from temperature measurements. Results show that radial and temporal variations of the boundary conditions have a strong influence on the homogeneity of heat extraction from the skin phantom. However, there is a subregion of uniform cooling whose size is time dependent. It is also observed that the surface heat flux undergoes a marked dynamic variation, with a maximum heat flux occurring at the centre of the sprayed surface early in the spurt followed by a quick decrease. The study shows that radial and temporal variations of boundary conditions must be taken into account and ideally controlled to guarantee uniform protection during CSC of human skin.
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
Heat-transfer dynamics during cryogen spray cooling of substrate at different initial temperatures
Physics in Medicine and Biology, 2004
Cryogen spray cooling (CSC) is used to minimize the fisk of epidermal damage during dermatologic therapy. However, the dominant mechanisms of heat transfer during the transient cooling process are incompletely understood. The objective of this study is to elucidate the physics of CSC by measuring the effect of initial substrate temperature (T-0) on cooling dynamics. Cryogen was delivered by a straight-tube nozzle onto a skin phantom. A fast-response thermocouple was used to record the phantom temperature changes before. during and after the cryogen spray. Surface heat fluxes (q") and heat-transfer coefficients (h) were computed using an inverse heat conduction algorithm. The maximum surface heat flux (q"(max)) was observed to increase with T-0. The surface temperature corresponding to q" also increased with T-0 but the latter has no significant effect on h. It is concluded that heat transfer between the cryogen spray and skin phantom remains in the nucleate boiling region even if T-0 is 80 degreesC.
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