Cooling efficiency of cryogen spray during laser therapy of skin (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.
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.
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.
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
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.
Evaluation of cryogen spray cooling exposure on in vitro model human skin
Lasers in Surgery and Medicine, 2004
Background and Objectives: Cryogen spray cooling (CSC) is commonly used during dermatologic laser surgery. The epidermal and dermal effects of CSC have not been adequately evaluated. To study the potential for epidermal and dermal injury after CSC using an in vitro model of human skin (RAFT). Study Design/Materials and Methods: RAFT specimens were exposed to continuous CSC spurt durations of 10, 20, 40, 80, 100, 200, or 500 milliseconds. Biopsies were taken acutely, 3 and 7 days post-CSC exposure. Sections were stained with hematoxylin and eosin for evaluation of possible injury, Ki-67 to determine keratinocyte viability, and Melan-A, to identify and evaluate melanocytes. Results: Minimal, transient epidermal changes were noted in specimens exposed to continuous CSC spurts of 80 milliseconds or less. Keratinocytes and melanocytes remained viable. Continuous CSC spurts of 100, 200, or 500 milliseconds (much longer than recommended for clinical use) resulted in significant epidermal injury acutely, with partial or full thickness epidermal necrosis at 7 days. Only the 500 milllisecond specimen demonstrated dermal change, decreased fibroblast proliferation at 3 days. Conclusions: Continuous CSC spurts of 80 milliseconds or less induce minimal, if any, epidermal or dermal damage and are unlikely to produce cryo-injury when used during dermatologic laser surgery.
In vitro evaluation of cryogen spray cooling exposure on model human skin
2004
Background and Objectives: Cryogen spray cooling (CSC) is commonly used during dermatologic laser surgery. The epidermal and dermal effects of CSC have not been adequately evaluated. To study the potential for epidermal and dermal injury after CSC using an in vitro model of human skin (RAFT). Study Design/Materials and Methods: RAFT specimens were exposed to continuous CSC spurt durations of 10, 20, 40, 80, 100, 200, or 500 milliseconds. Biopsies were taken acutely, 3 and 7 days post-CSC exposure. Sections were stained with hematoxylin and eosin for evaluation of possible injury, Ki-67 to determine keratinocyte viability, and Melan-A, to identify and evaluate melanocytes. Results: Minimal, transient epidermal changes were noted in specimens exposed to continuous CSC spurts of 80 milliseconds or less. Keratinocytes and melanocytes remained viable. Continuous CSC spurts of 100, 200, or 500 milliseconds (much longer than recommended for clinical use) resulted in significant epidermal injury acutely, with partial or full thickness epidermal necrosis at 7 days. Only the 500 milllisecond specimen demonstrated dermal change, decreased fibroblast proliferation at 3 days. Conclusions: Continuous CSC spurts of 80 milliseconds or less induce minimal, if any, epidermal or dermal damage and are unlikely to produce cryo-injury when used during dermatologic laser surgery.
Background and Objective: Dynamics of cryogen spray deposition, water condensation and frost formation is studied in relationship to cooling rate and ef®ciency 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 in¯uence of ambient humidity on heat extraction dynamics was measured in an atmosphere-controlled chamber using an epoxy block with embedded thermocouples.
Epidermal cooling during pulsed laser treatment of selected dermatoses
Medical Applications of Lasers III, 1996
The clinical objective in laser treatment of selected dermatoses such as port wine stain (PWS), hemangioma and telangiectasia is to maximize thermal damage to the blood vessels, while at the same time minimizing nonspecific injury to the normal overlying epidermis. "Dynamic" cooling of skin, whereby a cryogen is sprayed onto the surface for an appropriately short period of time (on the order of tens of milliseconds), may offer an effective method for eliminating epidermal thermal injury during laser treatment. We present theoretical and experimental investigations of the thermal response of skin to dynamic cooling in conjunction with pulsed laser irradiation at 585 nm. Computed temperature distributions indicate that cooling the skin immediately prior to pulsed laser irradiation with a cryogen spurt of tetrafluoroethane is an effective method for eliminating epidermal thermal injury during laser treatment of PWS. Experimental results show rapid reduction of skin surface temperature is obtained when using tetrafluoroethane spurts of 20-100 ms duration. Successful blanching of PWS without thermal injury to the overlying epidermis is accomplished.