Thermal Damage (thermal + damage)

Distribution by Scientific Domains

Selected Abstracts

The Effects of Variable Pulse Width of Er:YAG Laser on Facial Skin

Khalil A. Khatri MD
Background. The use of CO2 and Er:YAG lasers for resurfacing has increased significantly in the past few years. Er:YAG laser causes pinpoint bleeding during and after treatment with a typical pulse width of 250 ,sec. A longer pulse of Er:YAG laser can potentially coagulate dermal blood vessels and increase the residual thermal damage (RTD). Objective. To evaluate the effects of various pulse durations of Er:YAG laser on the depth of RTD and bleeding. Methods. The preauricular skin of a volunteer was exposed to Er:YAG laser at 250-, 350-, and 700-,sec pulse durations, with a fluence of 5 J/cm2. The number of passes varied between 6 and 16. The treated skin was excised and a histologic evaluation was done. Results. The maximum depth of RTD was 50 ,m and there was decreased bleeding with a 700-,sec pulse duration. Conclusion. The increased pulse duration of Er:YAG laser of 700 ,s does not increase the maximum reported RTD and therefore would not change the recovery time and may have a beneficial effect on hemostasis. [source]

Laser-Assisted Hair Transplantation: Histologic Comparison Between CO2 and Ho:YAG Lasers

Eugene A. Chu MD
Background. Various laser wavelengths and devices have been advocated for use in the creation of recipient channels during hair transplant surgery, including flash-scanned CO2, Ho:YAG (, = 2.12 ,m), and Er:YAG (, = 2.94 ,m). Objective. To determine the tissue injury caused by flash-scanned CO2 and pulsed Ho:YAG lasers during the creation of hair transplant recipient channels and to assess the efficacy of the Ho:YAG laser. Methods. Recipient channels were created in vivo in human scalp tissue using both lasers, and were excised and prepared for histologic examination. Optical micrometry of tissue sections was used to assess thermal injury. Results. The Ho:YAG laser created jagged, irregular-shaped channels with larger zones of thermal injury (superficial deepithelialization, thermal necrosis, and thermal damage). In contrast, the CO2 laser produced well-defined cylindrically shaped channels free of cellular debris with minimal epithelial disruption and significantly less lateral thermal injury. Conclusion. Given that the Ho:YAG produced larger regions of thermal injury and recipient channels that were unacceptable for graft, the CO2 laser remains the better choice for the creation of recipient channels during hair transplant surgery. However, ongoing research will be necessary to determine the optimal laser wavelength and/or devices for this procedure. [source]

Lasers for facial rejuvenation: a review

Evangelia Papadavid MD
Background Different types of laser are used for resurfacing and collagen remodeling in cutaneous laser surgery. Methods A systematic review was performed of the different types of laser currently employed for skin rejuvenation. These systems are either ablative [high-energy pulsed or scanned carbon dioxide (CO2) laser emitting at a wavelength of 10,600 nm, single- or variable-pulse or dual ablative/coagulative mode erbium:yttrium aluminum garnet (Er:YAG) laser emitting at a wavelength of 2940 nm, or systems combining both 10,600 nm and 2940 nm wavelengths] or nonablative [Q-switched neodymium:yttrium aluminum garnet (Nd:YAG) laser emitting at a wavelength of 1064 nm, Nd:YAG laser emitting at a wavelength of 1320 nm, or diode laser emitting at a wavelength of 1450 nm]. Different protocols, patient selection, treatment techniques, and complications are discussed for each system. Results New-generation CO2 resurfacing lasers have been successful in the treatment of photodamaged skin and scarring, with a postoperative morbidity dependent on the depth of thermal damage. Because of its minimal penetration, the pulsed Er:YAG laser, usually used in the treatment of more superficial rhytides, produces less postoperative morbidity. Novel ablative systems have been developed and a further understanding of laser,tissue interaction has led to the design of nonablative systems for the treatment of rhytides, scarring, and photodamaged skin, the efficacy and profile of which remain to be evaluated in the long term. Conclusions There are several effective techniques for scar revision and the treatment of aged skin, but all have their drawbacks due to a lack of precise depth control and unwanted damage to the lower layers of the dermis. The Er:YAG laser is the treatment of choice for fine lines and superficial scars, whereas the CO2 laser is better for deeper rhytides and scars. In the future, a combination of lasers may be used for facial rejuvenation. [source]

Safety of orthopedic implants in magnetic resonance imaging: An experimental verification

Ritabh Kumar
Abstract Magnetic resonance imaging (MRI) is an indispensable tool for musculoskeletal imaging. The presence of metal, however, raises concerns. The potential risks are loosening and migration of the implant, heating of the metal with surrounding tissue, causing thermal damage, and artifactual distortion which compromise the diagnostic value of the procedure. The aim of this study was to test experimentally the nature and extent of the first two of these effects in orthopedic implants. The degree of ferromagnetism was evaluated by deflection studies at the portals of a 0.25 Tesla permanent magnet and 1.0 Tesla clinical MRI scanner. None of the orthopedic implants exhibited any attraction. External fixator clamps, however, showed significant ferromagnetism. The heating of implants by "worst-case" scenario imaging sequences was insignificant. Many contemporary nonferromagnetic orthopedic implants can be imaged safely. It is prudent, however, to perform ex vivo deflection studies on a duplicate implant to confirm MR compatibility. With external fixator devices exhibiting strong ferromagnetism, MRI should be avoided. With expanding indications for MRI, orthopedic implants are unlikely to limit the potential of this powerful tool. 2006 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res [source]

Laser-Assisted Machining of Damage-Free Silicon Nitride Parts with Complex Geometric Features via In-Process Control of Laser Power

Yinggang Tian
A methodology to achieve optimal operating conditions for laser-assisted machining (LAM) is developed for silicon nitride parts with complex geometric features by applying a three-dimensional, transient thermal model and in-process laser power control. Complex silicon nitride parts are successfully produced by the LAM operation, where the maximum and material removal temperatures are carefully designed and controlled to achieve good machining results and avoid thermal damage on the final part. On-line temperature and laser power measurements are conducted and compared with prescribed values to show the effectiveness of the power control scheme. Scanning electron microscopy examination reveals virtually no subsurface microcrack or thermal damage on the silicon nitride parts. The X-ray diffraction (XRD) study shows the preservation of the silicon nitride microstructure and no phase transformation of ,-Si3N4 during the LAM experiments. XRD residual stress measurements show moderate compressive residual stresses on the silicon nitride workpieces produced by the LAM operation. [source]

Hyperthermic injury to adipocyte cells by selective heating of subcutaneous fat with a novel radiofrequency device: Feasibility studies

Walfre Franco PhD
Abstract Background and Objective The main objective of the present study is to demonstrate the feasibility of utilizing a novel non-invasive radiofrequency (RF) device to induce lethal thermal damage to subcutaneous adipose tissue only by establishing a controlled electric field that heats up fat preferentially. Study Design/Materials and Methods Adipocyte cells in six-well plates were subjected to hyperthermic conditions: 45, 50, 55, 60, and 65C during 1, 2, and 3,minutes. Cell viability was assessed 72,hours after exposure. Two groups of abdominoplasty patients were treated with the RF device during and days before their surgical procedure. Temperatures of cutaneous and subcutaneous tissues were measured during treatment (3,minutes) of the first group. The immediate tissue response to heating was assessed by acute histology. The delayed tissue response was assessed by histology analysis of the second group, 4, 9, 10, 17, and 24 days after treatment (22,minutes). A mathematical model was used to estimate treatment temperatures of the second group. The model uses patient-based diagnostic measurements as input and was validated with in vivo clinical temperature measurements. Results Cell viability dropped from 89% to 20% when temperature increased from 45 to 50C during 1,minute exposures. Three minutes at 45C resulted in 40% viability. In vivo, the temperature of adipose tissue at 7,12,mm depth from the surface increased to 50C while the temperature of cutaneous tissues was <30C during RF exposure. Acute and longitudinal histology evaluations show normal epidermal and dermal layers. Subcutaneous tissues were also normal acutely. Subcutaneous vascular alterations, starting at day 4, and fat necrosis, starting at day 9, were consistently observed within 4.5,19,mm depth from the skin surface. Subcutaneous tissue temperatures were estimated to be 43,45C for 15,minutes. Conclusions A controlled internal electric field perpendicular to the skin,fat interface is selective in heating up fat and, consequently, has the ability to induce lethal thermal damage to subcutaneous adipose tissues while sparing overlying and underlying tissues. In vitro adipocyte cells are heat sensitive to thermal exposures of 50 and 45C on the order of minutes, 1 and 3,minutes, respectively. In vivo, 15,minutes thermal exposures to 43,45C result in a delayed adipocyte cellular death response,in this study, 9 days. The novel RF device presented herein effectively delivers therapeutic thermal exposures to subcutaneous adipose tissues while protecting epidermal and dermal layers. Lasers Surg. Med. 42:361,370, 2010. 2010 Wiley,Liss, Inc. [source]

Intense pulsed light (IPL): A review

Philipp Babilas MD
Abstract Background Intense pulsed light (IPL) devices use flashlamps and bandpass filters to emit polychromatic incoherent high-intensity pulsed light of determined wavelength spectrum, fluence, and pulse duration. Similar to lasers, the basic principle of IPL devices is a more or less selective thermal damage of the target. The combination of prescribed wavelengths, fluences, pulse durations, and pulse intervals facilitates the treatment of a wide spectrum of skin conditions. Objective To summarize the physics of IPL, to provide guidance for the practical use of IPL devices, and to discuss the current literature on IPL in the treatment of unwanted hair growth, vascular lesions, pigmented lesions, acne vulgaris, and photodamaged skin and as a light source for PDT and skin rejuvenation. Methods A systematic search of several electronic databases, including Medline and PubMed and the authors experience on intense pulsed light. Results Numerous trials show the effectiveness and compatibility of IPL devices. Conclusion Most comparative trials attest IPLs similar effectiveness to lasers (level of evidence: 2b to 4, depending on the indication). However, large controlled and blinded comparative trials with an extended follow-up period are necessary. Lasers Surg. Med. 42:93,104, 2010. 2009 Wiley-Liss, Inc. [source]

Pulpal effects of enamel ablation with a microsecond pulsed ,,=,9.3-m CO2 laser

Michal Staninec DDS
Abstract Background and Objectives In vitro studies have shown that CO2 lasers operating at the highly absorbed 9.3 and 9.6-m wavelengths with a pulse duration in the range of 10,20-microsecond are well suited for the efficient ablation of enamel and dentin with minimal peripheral thermal damage. Even though these CO2 lasers are highly promising, they have yet to receive FDA approval. Clinical studies are necessary to determine if excessive heat deposition in the tooth may have any detrimental pulpal effects, particularly at higher ablative fluencies. The purpose of this study was to evaluate the pulpal safety of laser irradiation of tooth occlusal surfaces under the conditions required for small conservative preparations confined to enamel. Study Design/Materials and Methods Test subjects requiring removal of third molar teeth were recruited and teeth scheduled for extraction were irradiated using a pulsed CO2 laser at a wavelength of 9.3 m operating at 25 or 50 Hz using a incident fluence of 20 J/cm2 for a total of 3,000 laser pulses (36 J) for both rates with water cooling. Two control groups were used, one with no treatment and one with a small cut made with a conventional high-speed hand-piece. No anesthetic was used for any of the procedures and tooth vitality was evaluated prior to treatment by heat, cold and electrical testing. Short term effects were observed on teeth extracted within 72 hours after treatment and long term effects were observed on teeth extracted 90 days after treatment. The pulps of the teeth were fixed with formalin immediately after extraction and subjected to histological examination. Additionally, micro-thermocouple measurements were used to estimate the potential temperature rise in the pulp chamber of extracted teeth employing the same irradiation conditions used in vivo. Results Pulpal thermocouple measurements showed the internal temperature rise in the tooth was within safe limits, 3.31.4C without water cooling versus 1.71.6C with water-cooling, n,=,25, P<0.05. None of the control or treatment groups showed any deleterious effects on pulpal tissues and none of the 29 test-subjects felt pain or discomfort after the procedure. Only two test-subjects felt discomfort from "cold sensitivity" during the procedure caused by the water-spray. Conclusion It appears that this CO2 laser can ablate enamel safely without harming the pulp under the rate of energy deposition employed in this study. Lasers Surg. Med. 41:256,263, 2009. 2009 Wiley-Liss, Inc. [source]

Improvement of port wine stain laser therapy by skin preheating prior to cryogen spray cooling: A numerical simulation

Wangcun Jia PhD
Abstract 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. Lasers Surg. Med. 38:155,162, 2006. 2006 Wiley-Liss, Inc. [source]

Treatment of port wine stains with photodynamic therapy, using pulsed dye laser as a Light Source, Compared With Pulsed dye laser alone: A pilot study,

Alun V. Evans MRCP
Abstract Background and Objectives Laser-induced photo thermal damage has been combined with photodynamic therapy (PDT) using a systemic photosensitiser to treat vascular lesions. The efficacy of PDT using systemic 5-aminolaevulinic acid (5-ALA) as the photosensitiser and pulsed dye laser (PDL) as the light source in port wine stains (PWS) is unknown. Study Designs/Materials and Methods We conducted an internally controlled pilot study comparing the efficacy of PDT using PDL as a light source, to PDL alone in the treatment of PWS. Results The PWS improved slightly in all patients but no significant difference was found between the three treatment arms in terms of lesional lightening or incidence and severity of side effects. Conclusions There was no evidence of increased efficacy of PDT using PDL as a light source compared to PDL alone. There was also no significant difference in adverse events. Further studies using different treatment regimens over longer periods of time may be warranted. 2005 Wiley-Liss, Inc. [source]

Practical mathematical model to predict the performance of insulating packages

Seung-Jin Choi
Abstract Thermal insulation is used in a variety of applications to protect temperature-sensitive products from thermal damage. Several factors affect the performance of insulating packages. These factors include the packaging material, the geometry of the package, the geometry of the product, and the degree of contact between the product and the package. In this study, a comprehensive model which includes all of these factors was developed to predict the performance of the insulating package. First, an equation was derived for the calculation of the thermal resistance of a multilayered wall. The wall resistance was then used in a mathematical model which included the aforementioned factors. Basic heat transfer principles covering conduction, convection and radiation were applied to the model and the package heat penetration rate was calculated. Based on this model, several factors affecting the performance of the insulating package were discussed. Examples of the use of this model for ice requirement calculations were also included. Copyright 2007 John Wiley & Sons, Ltd. [source]

Linking isoprene with plant thermotolerance, antioxidants and monoterpene emissions

ABSTRACT The purpose of the present study was to test the possible plant thermotolerance role of isoprene and to study its relationship with non-enzymatic antioxidants and terpene emissions. The gas exchange, chlorophyll fluorescence, extent of photo- and oxidative stress, leaf damage, mechanisms of photo- and antioxidant protection, and terpene emission were measured in leaves of Quercus ilex seedlings exposed to a ramp of temperatures of 5 C steps from 25 to 50 C growing with and without isoprene (10 L L,1) fumigation. The results showed that isoprene actually conferred thermotolerance (shifted the decrease of net photosynthetic rates from 35 to 45 C, increased Fv/Fm at 50 C from 0.38 to 0.65, and decreased the leaf area damaged from 27 to 15%), that it precluded or delayed the enhancement of the antioxidant non-enzymatic defence conferred by , -tocopherol, ascorbic acid or , -carotene consumption in response to increasing temperatures, and that it decreased by approximately 70% the emissions of monoterpenes at the highest temperatures. This suggests that there are inducible mechanisms triggered by the initial stages of thermal damage that up-regulate these antioxidant compounds at high temperatures and that these mechanisms are somehow suppressed in the presence of exogenous isoprene, which seems to already exert an antioxidant-like behaviour. [source]

In vitro hydrolytic degradation of centrifugally spun polyhydroxybutyrate,pectin composite fibres

L John R Foster
Abstract BACKGROUND: Centrifugal spinning is a novel fibre-forming process that readily permits the incorporation of additives while avoiding the thermal damage often associated with conventional melt spinning. Centrifugal spinning of a viscous solution of poly(3-hydroxybutyrate) (PHB) mixed with pectin was used to fabricate a range of fibres containing different concentrations of this biologically active agent. The influence of this blending on fibre morphology and in vitro degradation in an accelerated hydrolytic model at 70 C and pH of 10.6 is reported. RESULTS: Blending influenced the physiochemical properties of the fibres, and this significantly affected the degradation profile of both the fibre and its PHB constituent. A greater influence on degradation was exerted by the type of pectin and its degree of esterification than by variations in its loading. CONCLUSION: Centrifugal spinning permits the fabrication of composite fibrous matrices from PHB and pectin. Incorporation of the polysaccharide into the fibres can be used to manipulate degradation behaviour and demonstrates a model for doping of matrices with active biological constituents. The unique features of the centrifugal spinning process, as illustrated by the structure of the fibres and the degradation profiles, suggest possible applications of centrifugally spun biopolymers as wound scaffolding devices and in tissue engineering. Copyright 2009 Society of Chemical Industry [source]

Liver resection using heat coagulative necrosis: indications and limits of a new method

Gregor A. Stavrou
Abstract Background:, A new approach towards achieving bloodless liver resection is the use of heat coagulative necrosis. The latest stage of this technique is a four-probe device (Habib Sealer), which we used for a variety of resections to find the best indications for the method. Methods:, Between 2005 and 2006 we performed 28 liver resections in 20 consecutive patients. The most common indication was metastatic colorectal cancer (75%). We treated a heterogeneous patient collective in terms of tumour localization and extent of resection. Resection was performed after creating a necrotic zone. The device achieved an area of coagulation of 1-cm width in which even larger vessels and bile ducts were safely sealed. Results:, Operative spectrum covered atypical resections (8), one- or bisegmentectomies at different locations (15), hemihepatectomies (4) and one extended right hepatectomy. With one exception intra-operative blood loss was lower than 100 mL. Four patients (20%) developed operation-related complications comprising abscess formation at the resection site. Follow-up shows tumour-free survival for 13 of 18 patients 12 months after resection. Conclusion:, Liver resection using the sealer device seems safe. In proximity of hilar structures or large vessels the method is not favourable for the fear of thermal damage. Extended resections are possible but not parenchyma saving. Good indications are atypical (deep) resections , especially in Segment IVb. [source]