Thermal cameras are used in research laboratories to measure tissue temperature during laser irra... more Thermal cameras are used in research laboratories to measure tissue temperature during laser irradiation. This study was an evaluation of the accuracy of a 3–5 μm thermal camera and two 8–12 μm cameras in detecting the maximum temperatures of small targets. The size of the targets was within the range of laser spot diameters which are used for vessel welding, angioplasty, and dermatology. The response to a sharp thermal edge was measured and analyzed for the three cameras, which had a scanning rate of 30 frames per second. The response of the 3–5 μm camera to reference black body targets of different sizes was also studied.It was found that the detector system required an average of 2.44 μs to reach 90% of maximum step response for the 8–12 μm system and 5.85 μs for the 3–5 μm system. With a 3×5 telescope and a 9.5 inch focal distance close-up lens, the 3–5 μm camera underestimated the temperature of targets smaller than 2.0 mm because of its slow detector response. Although the 8–12 μm camera provides more accurate measurements due to its faster detector response, it still underestimates the temperature of targets smaller than 900 μm, when similar magnification and focal distance are used.Methods to compensate for the inaccuracies are discussed, including empirical correction factors and the inverse filtering technique.
We investigated the ability of mathematical models to predict temperature rises in biological tis... more We investigated the ability of mathematical models to predict temperature rises in biological tissue duringlaser irradiation by comparing calculated values with experimental measurements. Samples of normal human aorta, beef myocardium, and polyacrylamide gel were irradiated in air with an argon laser beam, while surface temperatures were monitored with an IR camera. The effects of different surface boundary conditions in the model predictions were examined and compared with the experimental data. It was observed that, before a temperature of 60 degrees C was reached, the current mathematical models were capable of predicting tissue-surface temperature rises with an accuracy of 90% for a purely absorbing medium and with an accuracy of 75% for biological tissue (a scattering medium). Above 60 degrees C, however, the models greatly overestimated temperature rises in both cases. It was concluded that the discrepancieswere mainly a result of surface water vaporization, which was not considered in current models and which was by far the most significant surface-heat-loss mechanism for laser irradiation in air. The inclusion of surface water vaporization in the mathematical models provided a much better match between predicted temperatures and experimental results.
We compared the thermocoagulation effects of low power, slow heating (15 W x 180 seconds) versus ... more We compared the thermocoagulation effects of low power, slow heating (15 W x 180 seconds) versus high power, rapid heating (50 W x 60 seconds) laser regimens in the canine prostate. The study was performed in 20 mongrel canines. On each prostate, the low power regimen was delivered at the 2 and 4 o'clock positions, and the high power at the 8 and 10 o'clock positions. The laser power was measured at the fiber tip. Seven dogs (acute group) were sacrificed 1 hour after the procedure. The other 13 dogs (chronic group) were sacrificed at different time intervals from 3 days to 9 weeks after the procedure. The average depth of coagulation was significantly greater in lesions treated at low power (acute: 10.7 mm., chronic: 13.3 mm.) than in those treated at high power (acute: 8.5 mm., chronic: 11.6 mm.). Another potential benefit of the low power regimen observed in the study was preservation of the integrity and efficiency of the laser probe.
Background and Objective: Higher laser fluences than currently used in therapy (5-10 J/cm 2 ) are... more Background and Objective: Higher laser fluences than currently used in therapy (5-10 J/cm 2 ) are expected to result in more effective treatment of port wine stain (PWS) birthmarks. However, higher incident fluences increase the risk of epidermal damage caused by absorption of light by melanin. Cryogen spray cooling offers an effective method to reduce epidermal injury during laser irradiation. The objective of this study was to determine whether high laser incident fluences (15-30 J/cm 2 ) could be used while still protecting the epidermis in ex vivo human skin samples.
IEEE Journal of Selected Topics in Quantum Electronics, 1999
In many port wine stain (PWS) patients, successful clearing is not achieved even after multiple l... more 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 cryogen-phantom interface. Based on phantom measurements and model predictions, internal skin temperature reduction remains confined to the upper 400 μm 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 μm, and 4°C at a depth of 200 μm 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
Background and Objective: Cryogen spray cooling (CSC) is an effective method to reduce or elimina... more Background and Objective: Cryogen spray cooling (CSC) is an effective method to reduce or eliminate non-speci®c injury to the epidermis during laser treatment of various dermatological disorders. In previous CSC investigations, fuel injectors have been used to deliver the cryogen onto the skin surface. The objective of this study was to examine cryogen atomization and heat removal characteristics of various cryogen delivery devices. Study Design/Materials and Methods: Various cryogen delivery device types including fuel injectors, atomizers, and a device currently used in clinical settings were investigated. Cryogen mass was measured at the delivery device output ori®ce. Cryogen droplet size pro®ling for various cryogen delivery devices was estimated by optically imaging the droplets in¯ight. Heat removal for various cryogen delivery devices was estimated over a range of spraying distances by temperature measurements in an skin phantom used in conjunction with an inverse heat conduction model. Results: A substantial range of mass outputs were measured for the cryogen delivery devices while heat removal varied by less than a factor of two. Droplet pro®ling demonstrated differences in droplet size and spray density. Conclusions: Results of this study show that variation in heat removal by different cryogen delivery devices is modest despite the relatively large difference in cryogen mass output and droplet size. A non-linear relationship between heat removal by various devices and droplet size and spray density was observed.
Optical tweezers were used to characterize the mechanical properties of the outer hair cell (OHC)... more Optical tweezers were used to characterize the mechanical properties of the outer hair cell (OHC) plasma membrane by pulling tethers with 4.5-m polystyrene beads. Tether formation force and tether force were measured in static and dynamic conditions. A greater force was required for tether formations from OHC lateral wall (499 Ϯ 152 pN) than from OHC basal end (142 Ϯ 49 pN). The difference in the force required to pull tethers is consistent with an extensive cytoskeletal framework associated with the lateral wall known as the cortical lattice. The apparent plasma membrane stiffness, estimated under the static conditions by measuring tether force at different tether length, was 3.71 pN/m for OHC lateral wall and 4.57 pN/m for OHC basal end. The effective membrane viscosity was measured by pulling tethers at different rates while continuously recording the tether force, and estimated in the range of 2.39 to 5.25 pN⅐s/m. The viscous force most likely results from the viscous interactions between plasma membrane lipids and the OHC cortical lattice and/or integral membrane proteins. The information these studies provide on the mechanical properties of the OHC lateral wall is important for understanding the mechanism of OHC electromotility.
Thermal cameras are used in research laboratories to measure tissue temperature during laser irra... more Thermal cameras are used in research laboratories to measure tissue temperature during laser irradiation. This study was an evaluation of the accuracy of a 3–5 μm thermal camera and two 8–12 μm cameras in detecting the maximum temperatures of small targets. The size of the targets was within the range of laser spot diameters which are used for vessel welding, angioplasty, and dermatology. The response to a sharp thermal edge was measured and analyzed for the three cameras, which had a scanning rate of 30 frames per second. The response of the 3–5 μm camera to reference black body targets of different sizes was also studied.It was found that the detector system required an average of 2.44 μs to reach 90% of maximum step response for the 8–12 μm system and 5.85 μs for the 3–5 μm system. With a 3×5 telescope and a 9.5 inch focal distance close-up lens, the 3–5 μm camera underestimated the temperature of targets smaller than 2.0 mm because of its slow detector response. Although the 8–12 μm camera provides more accurate measurements due to its faster detector response, it still underestimates the temperature of targets smaller than 900 μm, when similar magnification and focal distance are used.Methods to compensate for the inaccuracies are discussed, including empirical correction factors and the inverse filtering technique.
We investigated the ability of mathematical models to predict temperature rises in biological tis... more We investigated the ability of mathematical models to predict temperature rises in biological tissue duringlaser irradiation by comparing calculated values with experimental measurements. Samples of normal human aorta, beef myocardium, and polyacrylamide gel were irradiated in air with an argon laser beam, while surface temperatures were monitored with an IR camera. The effects of different surface boundary conditions in the model predictions were examined and compared with the experimental data. It was observed that, before a temperature of 60 degrees C was reached, the current mathematical models were capable of predicting tissue-surface temperature rises with an accuracy of 90% for a purely absorbing medium and with an accuracy of 75% for biological tissue (a scattering medium). Above 60 degrees C, however, the models greatly overestimated temperature rises in both cases. It was concluded that the discrepancieswere mainly a result of surface water vaporization, which was not considered in current models and which was by far the most significant surface-heat-loss mechanism for laser irradiation in air. The inclusion of surface water vaporization in the mathematical models provided a much better match between predicted temperatures and experimental results.
We compared the thermocoagulation effects of low power, slow heating (15 W x 180 seconds) versus ... more We compared the thermocoagulation effects of low power, slow heating (15 W x 180 seconds) versus high power, rapid heating (50 W x 60 seconds) laser regimens in the canine prostate. The study was performed in 20 mongrel canines. On each prostate, the low power regimen was delivered at the 2 and 4 o'clock positions, and the high power at the 8 and 10 o'clock positions. The laser power was measured at the fiber tip. Seven dogs (acute group) were sacrificed 1 hour after the procedure. The other 13 dogs (chronic group) were sacrificed at different time intervals from 3 days to 9 weeks after the procedure. The average depth of coagulation was significantly greater in lesions treated at low power (acute: 10.7 mm., chronic: 13.3 mm.) than in those treated at high power (acute: 8.5 mm., chronic: 11.6 mm.). Another potential benefit of the low power regimen observed in the study was preservation of the integrity and efficiency of the laser probe.
Background and Objective: Higher laser fluences than currently used in therapy (5-10 J/cm 2 ) are... more Background and Objective: Higher laser fluences than currently used in therapy (5-10 J/cm 2 ) are expected to result in more effective treatment of port wine stain (PWS) birthmarks. However, higher incident fluences increase the risk of epidermal damage caused by absorption of light by melanin. Cryogen spray cooling offers an effective method to reduce epidermal injury during laser irradiation. The objective of this study was to determine whether high laser incident fluences (15-30 J/cm 2 ) could be used while still protecting the epidermis in ex vivo human skin samples.
IEEE Journal of Selected Topics in Quantum Electronics, 1999
In many port wine stain (PWS) patients, successful clearing is not achieved even after multiple l... more 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 cryogen-phantom interface. Based on phantom measurements and model predictions, internal skin temperature reduction remains confined to the upper 400 μm 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 μm, and 4°C at a depth of 200 μm 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
Background and Objective: Cryogen spray cooling (CSC) is an effective method to reduce or elimina... more Background and Objective: Cryogen spray cooling (CSC) is an effective method to reduce or eliminate non-speci®c injury to the epidermis during laser treatment of various dermatological disorders. In previous CSC investigations, fuel injectors have been used to deliver the cryogen onto the skin surface. The objective of this study was to examine cryogen atomization and heat removal characteristics of various cryogen delivery devices. Study Design/Materials and Methods: Various cryogen delivery device types including fuel injectors, atomizers, and a device currently used in clinical settings were investigated. Cryogen mass was measured at the delivery device output ori®ce. Cryogen droplet size pro®ling for various cryogen delivery devices was estimated by optically imaging the droplets in¯ight. Heat removal for various cryogen delivery devices was estimated over a range of spraying distances by temperature measurements in an skin phantom used in conjunction with an inverse heat conduction model. Results: A substantial range of mass outputs were measured for the cryogen delivery devices while heat removal varied by less than a factor of two. Droplet pro®ling demonstrated differences in droplet size and spray density. Conclusions: Results of this study show that variation in heat removal by different cryogen delivery devices is modest despite the relatively large difference in cryogen mass output and droplet size. A non-linear relationship between heat removal by various devices and droplet size and spray density was observed.
Optical tweezers were used to characterize the mechanical properties of the outer hair cell (OHC)... more Optical tweezers were used to characterize the mechanical properties of the outer hair cell (OHC) plasma membrane by pulling tethers with 4.5-m polystyrene beads. Tether formation force and tether force were measured in static and dynamic conditions. A greater force was required for tether formations from OHC lateral wall (499 Ϯ 152 pN) than from OHC basal end (142 Ϯ 49 pN). The difference in the force required to pull tethers is consistent with an extensive cytoskeletal framework associated with the lateral wall known as the cortical lattice. The apparent plasma membrane stiffness, estimated under the static conditions by measuring tether force at different tether length, was 3.71 pN/m for OHC lateral wall and 4.57 pN/m for OHC basal end. The effective membrane viscosity was measured by pulling tethers at different rates while continuously recording the tether force, and estimated in the range of 2.39 to 5.25 pN⅐s/m. The viscous force most likely results from the viscous interactions between plasma membrane lipids and the OHC cortical lattice and/or integral membrane proteins. The information these studies provide on the mechanical properties of the OHC lateral wall is important for understanding the mechanism of OHC electromotility.
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Papers by Jorge Torres