A New Ex Vivo Human Skin Burn Model

Currently, most burn models for preclinical testing are on animals. For obvious ethical, anatomical, and physiological reasons, these models could be replaced with optimized ex vivo systems. The creation of a burn model on human skin using a pulsed dye laser could represent a relevant model for preclinical research. Six samples of excess human abdominal skin were obtained within one hour after surgery. Burn injuries were induced on small samples of cleaned skin using a pulsed dye laser on skin samples, at varying fluences, pulse numbers and illumination duration. In total, 70 burn injuries were performed on skin ex vivo before being histologically and dermato-pathologically analyzed. Irradiated burned skin samples were classified with a specified code representing burn degrees. Then, a selection of samples was inspected after 14 and 21 days to assess their capacity to heal spontaneously and re-epithelize. We determined the parameters of a pulsed dye laser inducing first, second, and third degree burns on human skin and with fixed parameters, especially superficial and deep second degree burns. After 21 days with the ex vivo model, neo-epidermis was formed. Our results showed that this simple, rapid, user-independent process creates reproducible and uniform burns of different, predictable degrees that are close to clinical reality. Human skin ex vivo models can be an alternative to and complete animal experimentation, particularly for preclinical large screening. This model could be used to foster the testing of new treatments on standardized degrees of burn injuries and thus improve therapeutic strategies.

A new thermal dose model based on Vogel-Tammann-Fulcher behaviour in thermal damage processes

Thermal dose models are metrics that quantify the thermal effect on tissues based on the temperature and the time of exposure. These models are used to predict and control the outcome of hyperthermia (up to 45^°C) treatments, and of thermal coagulation treatments at higher temperatures (>45^°C). The validity and accuracy of the commonly used models (CEM43) are questionable when heating above the hyperthermia temperature range occurs, leading to an over-estimation of the accumulation of thermal damage. A new CEM43 dose model based on an Arrhenius-type, Vogel-Tammann-Fulcher, equation using published data, is introduced in this work. The new dose values for the same damage threshold that was produced at different in-vivo skin experiments were in the same order of magnitude, while the current dose values varied by two orders of magnitude. In addition, the dose values obtained using the new model for the same damage threshold in 6 lesions in ex-vivo liver experiments were more consistent than the current model dose values. The contribution of this work is to provide new modeling approaches to inform more robust thermal dosimetry for improved thermal therapy modeling, monitoring, and control.

Preclinical and clinical evaluation on the performance and safety of a novel energy-based device for body shaping: A pilot study

BACKGROUND

The emergence on the market of non-invasive mechanisms aimed at reducing subcutaneous fat achieving a slimming effect arouses great interest in doctors and patients. Several methods for the destruction of adipocytes are today on the market.

AIMS

This is a pilot study on body fat reduction treatment, using a novel energy-based device for body shaping.

METHODS

The study is performed on 42 patients, healthy adults of both sexes, with BMI between 25 and 30 kg/m², indicated for the removal of fatty tissue deposits specifically in the following areas: flanks, abdomen, internal legs, trochanter, buttocks, and arms. A minimum of 5 to a maximum of 6 treatments were performed for each patient, with the device, every two weeks and with a follow-up of 6 weeks. Circumference reduction, side effects, and patient pain were evaluated for all patients.

RESULTS

A set of 42 patients were evaluated. The mean circumference reduction at 6 weeks was 2.42 ± 0.4 cm (p < 0.001). Treatment was well-tolerated (pain score, 3.24 ± 1.03) by all patients. There were no adverse events and patients declared to be satisfied with the aesthetic results obtained with the treatment.

CONCLUSION

The new device emerges as a valid and safe treatment for all patients and shows a higher security profile with no side effects.

Nonuniform Exposure to the Cornea from Millimeter Waves

This study examines the nonuniform exposure to the cornea from incident millimeter waves at 94-100 GHz. Two previous studies measured temperature increases in the rhesus cornea exposed to brief (1-6 s) pulses of high-fluence millimeter waves (94 GHz), one of which also estimated thresholds for corneal damage (reported as ED50, the dose resulting in a visible lesion 50% of the time). Both studies noted large variations in the temperature increase across the surface of the cornea due to wave interference effects. This study examines this variability using high-resolution simulations of mm-wave absorption and temperature increase in the human cornea from exposures to plane wave energy at 100 GHz. Calculations are based on an earlier study. The simulations show that the peak temperature increases in the cornea from short exposures (up to 10 s) to high-intensity mm-wave pulses are 1.7-2.8 times the median increase depending on the polarization of the incident energy. A simple one-dimensional "baseline" model provides a good estimate of the median temperature increase in the cornea. Two different estimates are presented for the thresholds for producing thermal lesions, expressed in terms of the minimum fluence of incident 100 GHz pulses. The first estimate is based on thresholds for thermal damage from pulsed infrared energy, and the second is based on a thermal damage model. The mm-wave pulses presently considered far exceed current IEEE or ICNIRP exposure limits but may be produced by some nonlethal weapons systems. Interference effects due to wave reflections from structures in and near the eye result in highly localized variations in energy absorbed in the cornea and surrounding facial tissues and are important to consider in a hazard analysis for exposures to intense pulsed millimeter waves.

Strategy of boundary discretization in numerical simulation of laser propagation in skin tissue with vascular lesions

Understanding light propagation in skin tissues with complex blood vessels can help improve clinical efficacy in the laser treatment of cutaneous vascular lesions. The voxel-based Monte Carlo (VMC) algorithm with simple blood vessel geometry is commonly used in studying the law of light propagation in tissues. However, unavoidable errors are expected in VMC because of the zigzag polygonal interface. A tetrahedron-based Monte Carlo with extended boundary condition (TMCE) solver is developed to discretize complex tissue boundaries accurately. Tetrahedra are generated along the interface, resulting in a polyhedron approximation to match the real interface. A comparison between TMCE and VMC shows neglected differences in the overall distribution of energy deposition of different models, but poor adaptability of the curved tissue interface in VMC leads to a higher energy deposition error than TMCE in a mostly deposited region in blood vessels. Replacing the real blood vessel with a cylinder-shaped vessel shows an error lower than that caused by VMC. Statistical significance analysis of energy deposition by TMCE shows that mean curvature has stronger relationship with energy deposition than the Gaussian curvature, which indicates the importance of this geometric parameter in predicting photon behavior in vascular lesions.

Porcine skin damage threshold from mid-infrared optical parametric oscillator radiation at 3.743 µm

There is increasing use of mid-infrared optical parametric oscillator radiation operating in the wavelength range of 3-5 µm. To expand existing damage data for skin exposure to lasers in this wavelength region, the in-vivo damage threshold at the wavelength of 3.743 µm was determined in a Guizhou miniature pig model for an exposure duration of 1.0 s. The irradiance of the laser spot was nearly Gaussian-distributed and the 1/e² beam diameter on the animal skin surface was fixed at 0.94 and 0.88 cm along horizontal and vertical directions. Damage lesion determinations were performed at 1- and 24-hour post-exposure. The probit analysis was employed to establish the ED₅₀ values. The ED₅₀ expressed in peak radiant exposure for the Gaussian spot was 4.04 J/cm² at the 24-hour post-exposure. Sufficient margin existed between the damage threshold and MPE from the current laser safety standard. The obtained data may contribute to the knowledge base for refinement of laser safety standard in the wavelength range of 2.6-1000 µm.

Comparison of different energy response for lipolysis using a 1,060-nm laser: An animal study of three pigs

BACKGROUND

Non-invasive body-sculpting procedures are becoming increasingly popular. The application of 1,060 nm of laser energy transcutaneously to hyperthermically induce the disruption of fat cells in the abdomen is a type of non-invasive procedure.

AIMS

The purpose of this study was to compare the treatment results from two parameters of the same system, each with different energy output levels, in an in vivo porcine model to determine the most effective application.

METHODS

Female pigs (n = 3) were used in this study. We examined the effects of the treatment using photography, ultrasonography, gross and microscopic pathology, and histological examination in order to determine the mechanism of action, efficacy, and safety of the procedure. Blood chemistry analysis was performed before each session to check lipid levels and to monitor for any adverse changes in markers that may indicate liver damage. Biopsies were taken and routinely processed with hematoxylin and eosin and Oil Red O stains to examine for tissue damage at baseline and after each treatment. Terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick end labeling (TUNEL) assays were performed to check for apoptotic-related DNA damage.

RESULTS

Ultrasonic imaging of the same area before and after the application of 1,060 nm of laser energy at outputs of 0.9 and 1.4 W/cm² showed that the density of the fat layer changed immediately after irradiation due to the transient heat transfer in the fat layer. Preclinical evaluation was performed to obtain comparison data on the safety and efficacy of subcutaneous fat reduction after applying the different energy outputs of 0.9 and 1.4 W/cm² .

CONCLUSION

Based on our findings, we suggest that long-term histologic changes through the use of these devices suggest a comparative effectiveness of the treatment energy.

Theoretical Study on Pressure Damage Based on Clinical Purpura during the Laser Irradiation of Port Wine Stains with Real Complex Vessels

Port wine stains (PWSs) are congenital dermal vascular lesions composed of a hyperdilated vasculature. Purpura represented by local hemorrhage from water vaporization in blood during laser therapy of PWS is typically considered a clinical feedback, but with a low cure rate. In this study, light propagation and heat deposition in skin and PWSs is simulated by a tetrahedron-based Monte Carlo method fitted to curved bio-tissues. A curvature-corrected pressure damage model was established to accurately evaluate the relationship between purpura-bleeding area (rate) and laser therapy strategy for real complex vessels. Results showed that the standard deviation of Gaussian curvature of the vessel wall has negative relation with the fluence threshold of vessel rupture, but has positive relation with the effective laser fluence of vessel damage. This finding indicated the probable reason for the poor treatment of PWS, that is, considering purpura formation as a treatment end point (TEP) only leads to partial removal of vascular lesions. Instead, appropriate purpura area ratio with marked effects or rehabilitation should be adopted as TEP. The quantitative correlation between the fluence of a pulsed dye laser and the characteristics of vascular lesions can provide personalized and precise guidance for clinical treatments.

The Impact of Proteomic Investigations on the Development and Improvement of Skin Laser Therapy: A Review Article

Introduction: Different molecular approaches have contributed to finding various responses of skin to external and internal tensions such as laser irradiation and many important mediators of skin disease have been identified through these approaches. However, different essential signals of skin biomarker pathways and proteins are partially detected or completely unknown. In the present study, the impact of proteomics on the evaluation of laser therapy for the treatment of skin diseases is investigated. Methods: The keywords of "Proteomics", "Laser therapy", "Skin", and "Skin disease" were searched in Google Scholar, Scopus and PubMed search engines. After screening, 53 documents were included in the study. Results: The global assessments revealed that different proteins in different signaling pathways of skin metabolism in terms of health or illness after laser therapy are expressed differentially. The results indicated that the application of proteomics is a useful method for promoting the results of laser interventions. Conclusion: This kind of research dealt with the practical proteomics of skin diseases and skin laser therapy.

The influence of morphological distribution of melanin on parameter selection in laser thermotherapy for vascular skin diseases

Port wine stains (PWSs) are congenital vascular malformations that progressively darken and thicken with age. Currently, laser therapy is the most effective way in clinical management of PWS. It is known that skin pigmentation (melanin content) affects the radiant exposure that can be safely applied to treat PWS. However, the effect of melanin distribution in the epidermis on the maximum safe radiant exposure has not been studied previously. In this study, 10 different morphological distributions of melanin were proposed according to the formation and migration characteristics of melanin, and the two-scale heat transfer model was employed to investigate the influence of melanin distribution on the threshold radiant exposure of epidermis and blood vessels. The results show that melanin distributions do have a strong effect on laser parameter selection. When uniform melanin distribution is assumed, the threshold radiant exposure to damage a typical PWS blood vessel (50 μm diameter) is 8.62 J/cm² lower than that to injure epidermis. The optimal pulse duration is 1-5 ms for a typical PWS blood vessel of 50 μm when melanin distribution is taken into consideration. PWS blood vessels covered by non-uniformly distributed melanin are more likely to have poor response to laser treatment.

A pilot clinical trial of a near-infrared laser vaccine adjuvant: safety, tolerability, and cutaneous immune cell trafficking

Many vaccines require adjuvants to enhance immunogenicity, but there are few safe and effective intradermal (i.d.) adjuvants. Murine studies have validated the potency of laser illumination of skin as an adjuvant for i.d. vaccination with advantages over traditional adjuvants. We report a pilot clinical trial of low-power, continuous-wave, near-infrared laser adjuvant treatment, representing the first human trial of the safety, tolerability, and cutaneous immune cell trafficking changes produced by the laser adjuvant. In this trial we demonstrated a maximum tolerable energy dose of 300 J/cm2 to a spot on the lower back. The irradiated spot was biopsied 4 h later, as was a control spot. Paired biopsies were submitted for histomorphologic and immunohistochemical evaluation in a blinded fashion as well as quantitative PCR analysis for chemokines and cytokines. Similar to prior murine studies, highly significant reductions in CD1a+ Langerhans cells in the dermis and CD11c+ dermal dendritic cells were observed, corresponding to the increased migratory activity of these cells; changes in the epidermis were not significant. There was no evidence of skin damage. The laser adjuvant is a safe, well-tolerated adjuvant for i.d. vaccination in humans and results in significant cutaneous immune cell trafficking.-Gelfand, J. A., Nazarian, R. M., Kashiwagi, S., Brauns, T., Martin, B., Kimizuka, Y., Korek, S., Botvinick, E., Elkins, K., Thomas, L., Locascio, J., Parry, B., Kelly, K. M., Poznansky, M. C. A pilot clinical trial of a near-infrared laser vaccine adjuvant: safety, tolerability, and cutaneous immune cell trafficking.

Silicon arrayed waveguide gratings at 2.0-μm wavelength characterized with an on-chip resonator

Low-loss arrayed waveguide gratings (AWGs) are demonstrated at a 2.0-μm wavelength. These devices promote rapidly developing photonic applications, supported by the recent development of mid-infrared lasers integrated on silicon (Si). Multi-spectral photonic integrated circuits at 2.0-μm are envisioned since the AWGs are fabricated with the 500-nm-thick Si-on-insulator platform compatible with recently demonstrated lasers and semiconductor optical amplifiers on Si. Characterization with the AWG-ring method improves the on-chip transmission uncertainty to ∼6% compared to the conventional method with an uncertainty of ∼53%. Channel losses of ∼2.4  dB are found, with -31  dB crosstalk per channel. Fully integrated multi-spectral sources at 2.0 μm with pump lasers, low-loss multiplexers, and an output amplifier are now feasible.

Evaluation of the Photothermal Properties of a Reduced Graphene Oxide/Arginine Nanostructure for Near-Infrared Absorption

Strong near-infrared (NIR) absorption of reduced graphene oxide (rGO) make this material a candidate for photothermal therapy. The use of rGO has been limited by low stability in aqueous media due to the lack of surface hydrophilic groups. We report synthesis of a novel form of reduced graphene-arginine (rGO-Arg) as a nanoprobe. Introduction of Arg to the surface of rGO not only increases the stability in aqueous solutions but also increases cancer cell uptake. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) images are recorded to characterize the morphology of rGO-Arg. Fourier transform infrared (FTIR), X-ray photoelectron spectra (XPS), Raman, and UV-vis spectroscopy are utilized to analyze the physiochemical properties of rGO-Arg. Interaction of rGO-Arg with 808 nm laser light has been evaluated by measuring the absorption cross section in response to periodically modulated intensity to minimize artifacts arising from lateral thermal diffusion with a material scattering matched to a low scattering optical standard. Cell toxicity and cellular uptake by MD-MB-231 cell lines provide supporting data for the potential application of rGO-Arg for photothermal therapy. Absorption cross-section results suggest rGO-Arg is an excellent NIR absorber that is 3.2 times stronger in comparison to GO.

Autofluorescence spectroscopy for nerve-sparing laser surgery of the head and neck-the influence of laser-tissue interaction

The use of remote optical feedback systems represents a promising approach for minimally invasive, nerve-sparing laser surgery. Autofluorescence properties can be exploited for a fast, robust identification of nervous tissue. With regard to the crucial step towards clinical application, the impact of laser ablation on optical properties in the vicinity of structures of the head and neck has not been investigated up to now. We acquired 24,298 autofluorescence spectra from 135 tissue samples (nine ex vivo tissue types from 15 bisected pig heads) both before and after ER:YAG laser ablation. Sensitivities, specificities, and area under curve(AUC) values for each tissue pair as well as the confusion matrix were statistically calculated for pre-ablation and post-ablation autofluorescence spectra using principal component analysis (PCA), quadratic discriminant analysis (QDA), and receiver operating characteristics (ROC). The confusion matrix indicated a highly successful tissue discrimination rate before laser exposure, with an average classification error of 5.2%. The clinically relevant tissue pairs nerve/cancellous bone and nerve/salivary gland yielded an AUC of 100% each. After laser ablation, tissue discrimination was feasible with an average classification accuracy of 92.1% (average classification error 7.9%). The identification of nerve versus cancellous bone and salivary gland performed very well with an AUC of 100 and 99%, respectively. Nerve-sparing laser surgery in the area of the head and neck by means of an autofluorescence-based feedback system is feasible even after ER-YAG laser-tissue interactions. These results represent a crucial step for the development of a clinically applicable feedback tool for laser surgery interventions in the oral and maxillofacial region.

Subcutaneous adipose tissue response to a non-invasive hyperthermic treatment using a 1,060 nm laser

BACKGROUND

We postulated that a hyperthermic treatment using a 1,060 nm laser can cause a controlled adipocyte injury resulting in non-invasive fat reduction. This three-part study identified treatment parameters for a safe and tolerable treatment, demonstrated short- and long-term tissue response, and assessed the potential of this treatment for non-invasive fat reduction.

METHODS

In vivo temperature measurements were conducted prior to abdominoplasty via a thermal camera (for surface readings) and thermocouple needle (for subcutaneous readings). Short- and long-term tissue response was evaluated on the abdomen immediately post to 6 months post a 1,060 nm laser treatment. Laser dosage was varied to identify safe and effective parameters for fat reduction. Tissue biopsies for hematoxylin/eosin (H&E) staining were taken at weeks 1 and 2, as well as at 1, 2, 3, and 6 months (if applicable). Additionally, six subjects received a hyperthermic laser treatment to the flanks; four patients receiving laser treatment to one flank and cryolipolysis on the other, and two patients receiving laser treatment on one side with the other side as an untreated control. Efficacy measurements included ultrasound measurement of fat thickness at baseline, 2, 3, and 6 months; Magnetic Resonance Imaging (MRI) to calculate fat volume at baseline, 3 and 6 months; and blinded photograph evaluation at baseline, 1, 2, 3, and 6 months.

RESULTS

In vivo temperature measurements demonstrated that the hyperthermic temperature target (42-47°C) can be achieved and maintained in subcutaneous adipose tissue via a 1,060 nm laser in conjunction with surface cooling. Short- and long-term tissue responses were evaluated by tissue histology up to 6 months following treatment. Histological changes included inflammation, followed by macrophage infiltration starting at approximately 2 weeks, with evacuation of cellular debris completed by approximately 6 months. Clinical results demonstrated average fat thickness reduction at 14%, 18%, and 18% at 2, 3, and 6 months, respectively. Average fat volume reduction measured by MRI at 3 and 6 months was 24% and 21%, respectively. Blinded photo evaluation showed improvement starting at 1-month post-treatment and was maintained at 6 months. Adverse events were rare and included mild tenderness that resolved by 1-week post-treatment.

CONCLUSION

Parameters were identified that selectively injure and reduce adipocytes in subcutaneous tissue using a 1,060 nm externally applied laser. The treatment had an excellent safety profile and was well tolerated. The clinical study demonstrated that a 1,060 nm hyperthermic laser treatment for non-invasive fat reduction can be safe and effective. Lasers Surg. Med. 49:480-489, 2017. © 2016 Wiley Periodicals, Inc.

The effects of 1064 nm Nd:YAG laser irradiation under the different treatment conditions for skin rejuvenation: quantitative and histologic analyses

OBJECTIVE

The aim of this study was to estimate heat distributions and evaluate degrees of tissue damages histologically after transmitting therapeutic lasers to find optimum ranges for skin rejuvenation.

BACKGROUND DATA

To treat skin aging, many researchers attempted to evaluate treatment effects for the different approaches. The noninvasive skin rejuvenation method was mostly employed to optimize the therapeutic effects by quantifying the laser conditions. However, current approaches produced low reliability for predicting tissue damage.

METHODS

We transmitted the 1064 nm Nd:YAG laser into a skin-mimicking phantom and pig skin samples according to the different fluences and spot diameters, and analyzed its internal-external temperatures. For histologic analyses, we also stained pig skin samples with hematoxylin and eosin (H&E) and compared degrees of tissue damage. The spot diameter conditions were classified into 5, 8, and 10 mm, and the fluence conditions were divided into 26, 30, and 36 J/cm(2). In addition, the pulse duration was set to 30 ms.

RESULTS

In our experiments, the conditions of a spot diameter of 5 mm with a fluence of 36 J/cm(2) and a spot diameter of 10 mm with a fluence of 26 J/cm(2) yielded the maximum surface temperatures>40°C. Regarding histologic evaluations, we also found that the degrees of internal thermal injuries are worsened as spot diameters and fluences increased.

CONCLUSIONS

We selected the optimum treatment conditions for skin rejuvenation as being the laser condition of a spot diameter of 5 mm with a fluence of 36 J/cm(2) and a spot diameter of 10 mm with a fluence of 26 J/cm(2).

Near-infrared-actuated devices for remotely controlled drug delivery

A reservoir that could be remotely triggered to release a drug would enable the patient or physician to achieve on-demand, reproducible, repeated, and tunable dosing. Such a device would allow precise adjustment of dosage to desired effect, with a consequent minimization of toxicity, and could obviate repeated drug administrations or device implantations, enhancing patient compliance. It should exhibit low off-state leakage to minimize basal effects, and tunable on-state release profiles that could be adjusted from pulsatile to sustained in real time. Despite the clear clinical need for a device that meets these criteria, none has been reported to date to our knowledge. To address this deficiency, we developed an implantable reservoir capped by a nanocomposite membrane whose permeability was modulated by irradiation with a near-infrared laser. Irradiated devices could exhibit sustained on-state drug release for at least 3 h, and could reproducibly deliver short pulses over at least 10 cycles, with an on/off ratio of 30. Devices containing aspart, a fast-acting insulin analog, could achieve glycemic control after s.c. implantation in diabetic rats, with reproducible dosing controlled by the intensity and timing of irradiation over a 2-wk period. These devices can be loaded with a wide range of drug types, and therefore represent a platform technology that might be used to address a wide variety of clinical indications.

A two-temperature model for selective photothermolysis laser treatment of port wine stains

Selective photothermolysis is the basic principle for laser treatment of vascular malformations such as port wine stain birthmarks (PWS). During cutaneous laser surgery, blood inside blood vessels is heated due to selective absorption of laser energy, while the surrounding normal tissue is spared. As a result, the blood and the surrounding tissue experience a local thermodynamic non-equilibrium condition. Traditionally, the PWS laser treatment process was simulated by a discrete-blood-vessel model that simplifies blood vessels into parallel cylinders buried in a multi-layer skin model. In this paper, PWS skin is treated as a porous medium made of tissue matrix and blood in the dermis. A two-temperature model is constructed following the local thermal non-equilibrium theory of porous media. Both transient and steady heat conduction problems are solved in a unit cell for the interfacial heat transfer between blood vessels and the surrounding tissue to close the present two-temperature model. The present two-temperature model is validated by good agreement with those from the discrete-blood-vessel model. The characteristics of the present two-temperature model are further illustrated through a comparison with the previously-used homogenous model, in which a local thermodynamic equilibrium assumption between the blood and the surrounding tissue is employed.

Effect of laser thermal injury on Langerhans cells in mouse and hairless guinea pig epidermis

To examine the effect of laser thermal injury on Langerhans cells (LC) within the epidermis, the dorsal skin of mice and hairless guinea pigs was exposed to varying levels of laser irradiation using a thulium laser at a wavelength of 2.0 μm. At 6, 24 and 48 h post irradiation, animals were euthanized, skin samples prepared for histology and the epidermis obtained and stained by major histocompatibility complex-II staining (mice) or ATPase assay (hairless guinea pigs) for the enumeration of LC. Mouse skin exhibited histological evidence of thermal damage at 24 h post irradiation at even the lowest dose (0.14 W) and decreases in the numbers of epidermal LC were observed at all doses and decreases were proportional to dose. In contrast, hairless guinea pig skin only showed consistent histological evidence of thermal damage at the highest dose of irradiation (0.70 W) at 24 and 48 h post irradiation and exhibited a statistically significant decrease in numbers of epidermal LC only at this dose. Thus, epidermal LC depletion occurred in the skin of both mice and hairless guinea pigs in response to laser treatment and the magnitude of depletion directly correlated with the extent of thermal damage both within and between species.

Skin burns after laser exposure: histological analysis and predictive simulation

Thermal effects of laser irradiation on skin are investigated in this paper. The main purpose is to determine the damage level induced by a laser exposure. Potential burns induced by two lasers (wavelength 808nm and 1940nm) are studied and animal experimentations are performed. Several exposure durations and laser powers are tested. Based on previous works, a mathematical model dedicated to temperature prediction is proposed and finite-element method is implemented. This numerical predictive tool based on the bioheat equation takes into account heat losses due to the convection on skin surface, blood circulatory and also evaporation. Thermal behavior of each skin layer is also described considering distinct thermal and optical properties. Since the mathematical model is able to estimate damage levels, histological analyses were also carried through. It is confirmed that the mathematical model is an efficient predictive tool for estimation of damage caused by lasers and that thermal effects sharply depend on laser wavelength.

Three-dimensional Monte Carlo model of pulsed-laser treatment of cutaneous vascular lesions

We present a three-dimensional Monte Carlo model of optical transport in skin with a novel approach to treatment of side boundaries of the volume of interest. This represents an effective way to overcome the inherent limitations of "escape" and "mirror" boundary conditions and enables high-resolution modeling of skin inclusions with complex geometries and arbitrary irradiation patterns. The optical model correctly reproduces measured values of diffuse reflectance for normal skin. When coupled with a sophisticated model of thermal transport and tissue coagulation kinetics, it also reproduces realistic values of radiant exposure thresholds for epidermal injury and for photocoagulation of port wine stain blood vessels in various skin phototypes, with or without application of cryogen spray cooling.

Injury depth control from combined wavelength and power tuning in scanned beam laser thermal therapy

Laser thermal therapy represents a possible method to treat premalignant epithelial lesions of the esophagus. Dynamically conforming the thermal injury profile to a specific lesion boundary is expected to improve the efficacy of such a treatment and avoid complications. In this work, we investigated wavelength tuning as a mechanism to achieve this aimed control over injury depth by using the strong variation of water absorption close to 1900 nm. We developed a numerical model simulating in steps the photon propagation in the tissue, the diffusion of the absorbed heat, and the resulting tissue damage. The model was compared with experimental results on porcine esophageal specimens ex vivo and showed good agreement. Combined with power tuning, the wavelength agility in the range of 1860 to 1895 nm extends the injury range compared to a fixed wavelength source beyond 1 mm, while at the same time improving control over shallow depths and avoiding vaporization at the tissue surface. The combination of two or three discrete wavelengths combined at variable ratios provides similar control, and may provide an improved strategy for the treatment of endothelial lesions.

Numerical optimization of sequential cryogen spray cooling and laser irradiation for improved therapy of port wine stain

BACKGROUND AND OBJECTIVE

Despite application of cryogen spray (CS) precooling, customary treatment of port wine stain (PWS) birthmarks with a single laser pulse does not result in complete lesion blanching for a majority of patients. One obvious reason is nonselective absorption by epidermal melanin, which limits the maximal safe radiant exposure. Another possible reason for treatment failure is screening of laser light within large PWS vessels, which prevents uniform heating of the entire vessel lumen. Our aim is to identify the parameters of sequential CS cooling and laser irradiation that will allow optimal photocoagulation of various PWS blood vessels with minimal risk of epidermal thermal damage.

STUDY DESIGN AND METHODS

Light and heat transport in laser treatment of PWS are simulated using a custom 3D Monte Carlo model and 2D finite element method, respectively. Protein denaturation in blood and skin are calculated using the Arrhenius kinetic model with tissue-specific coefficients. Simulated PWS vessels with diameters of 30-150 µm are located at depths of 200-600 µm, and shading by nearby vessels is accounted for according to PWS histology data from the literature. For moderately pigmented and dark skin phototypes, PWS blood vessel coagulation and epidermal thermal damage are assessed for various parameters of sequential CS cooling and 532-nm laser irradiation, i.e. the number of pulses in a sequence (1-5), repetition rate (7-30 Hz), and radiant exposure.

RESULTS

Simulations of PWS treatment in darker skin phototypes indicate specific cooling/irradiation sequences that provide significantly higher efficacy and safety as compared to the customary single-pulse approach across a wide range of PWS blood vessel diameters and depths. The optimal sequences involve three to five laser pulses at repetition rates of 10-15 Hz.

CONCLUSIONS

Application of the identified cooling/irradiation sequences may offer improved therapeutic outcome for patients with resistant PWS, especially in darker skin phototypes.

Hematopoietic radiation syndrome in the Gottingen minipig

Additional large animal models for the acute radiation syndrome (ARS) would facilitate countermeasure development. We demonstrate here that Gottingen minipigs develop hematopoietic ARS symptoms similar to those observed in canines, non-human primates (NHPs) and humans. Dosimetry for whole-body γ irradiation (0.6 Gy/min) was performed using electronic paramagnetic resonance (EPR) with alanine; National Institute of Standards and Technology (NIST)-calibrated alanine pellets and water-filled Plexiglas phantoms were used. After irradiations of 1.6-2.0 Gy, blood pancytopenia was observed for several weeks, accompanied by the characteristic ARS stages: prodromal symptoms, latent period, illness and recovery or morbidity. Morbidity occurred between days 14 and 27, with a preliminary LD(50/30) estimate between 1.7 and 1.9 Gy. The criterion of whether platelet counts were <200 × 10(3)/µl 7 days postirradiation predicted whether animals would survive in 18 out of 20 cases. The degree of granulocytosis 3 h postirradiation was inversely correlated with survival. Animals euthanized based on preset morbidity criteria displayed signs of multi-organ dysfunction, including widespread internal hemorrhage and alterations in organ function reflected in blood chemistry. Circulating C-reactive protein (CRP), a marker for inflammation, became elevated within hours after irradiation, subsided after several days, and increased again after 14 days. The results support further development of the Gottingen minipig as a model for ARS.

Mathematical model that describes the transition from thermal to photochemical damage in retinal pigment epithelial cell culture

We propose a rate process model for describing photochemical damage to retinal cells by short wavelength laser exposures. The rate equation for photochemical damage contains a positive rate that is temperature independent, and a negative (quenching) rate that is temperature dependent. Using the traditional Arrhenius integral to describe thermal damage, we derive damage threshold doses for both thermal and photochemical mechanisms, and show that the model accounts for the sharp transition from thermal to photochemical damage thresholds that have recently been observed in an in-vitro retinal model.

Noninvasive assessment of burn wound severity using optical technology: a review of current and future modalities

Clinical examination alone is not always sufficient to determine which burn wounds will heal spontaneously and which will require surgical intervention for optimal outcome. We present a review of optical modalities currently in clinical use and under development to assist burn surgeons in assessing burn wound severity, including conventional histology/light microscopy, laser Doppler imaging, indocyanine green videoangiography, near-infrared spectroscopy and spectral imaging, in vivo capillary microscopy, orthogonal polarization spectral imaging, reflectance-mode confocal microscopy, laser speckle imaging, spatial frequency domain imaging, photoacoustic microscopy, and polarization-sensitive optical coherence tomography.

Fluence of thulium laser system in skin ablation

Tm:YAP laser system at power levels up to 1.2 W at 1980 nm was established in both continuous-wave and modulated modes of operation. The fluence effect of the laser system for skin ablation was analyzed by histology analysis with Wistar rat skin tissues. Thermally altered length, thermally altered area, ablation area, and ablation depth parameters were measured on histology images of skin samples just after the laser operation and after four-day healing period. Continuous-wave mode of operation provided higher thermal effects on the skin samples. Lower fluence levels were found for efficient ablation effect.

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

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 65 degrees C 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 50 degrees C during 1 minute exposures. Three minutes at 45 degrees C resulted in 40% viability. In vivo, the temperature of adipose tissue at 7-12 mm depth from the surface increased to 50 degrees C while the temperature of cutaneous tissues was <30 degrees C 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 43-45 degrees C 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 45 degrees C on the order of minutes, 1 and 3 minutes, respectively. In vivo, 15 minutes thermal exposures to 43-45 degrees C 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.

Infrared skin damage thresholds from 1940-nm continuous-wave laser exposures

A series of experiments are conducted in vivo using Yucatan mini-pigs (Sus scrofa domestica) to determine thermal damage thresholds to the skin from 1940-nm continuous-wave thulium fiber laser irradiation. Experiments employ exposure durations from 10 ms to 10 s and beam diameters of approximately 4.8 to 18 mm. Thermal imagery data provide a time-dependent surface temperature response from the laser. A damage endpoint of minimally visible effect is employed to determine threshold for damage at 1 and 24 h postexposure. Predicted thermal response and damage thresholds are compared with a numerical model of optical-thermal interaction. Results are compared with current exposure limits for laser safety. It is concluded that exposure limits should be based on data representative of large-beam exposures, where effects of radial diffusion are minimized for longer-duration damage thresholds.

In vivo comparison of near infrared lasers for skin welding

The skin closure abilities of near infrared lasers and suturing were compared by histological examination and mechanical tensile tests during a 21-day healing period. One-centimeter incisions on the dorsal skin of Wistar rats were treated by one of the closing techniques: (a) soldering, using an 809 nm diode laser (0.5 W, 5 s) with 25% bovine serum albumin (BSA) and 2.5 mg/ml indocyanine green (ICG); (b) direct welding with a 980 nm diode laser (0.5 W, 5 s); (c) direct welding with a 1,070 nm fiber laser (0.5 W, 5 s); (d) suturing. Six spots (79.61 J/cm(2) for each spot) were applied through the incisions. Healing was inspected on the 1st, 4th, 7th, 14th, and 21st post-operative days. The closure index (CI), thermally altered area (TAA), granulation area (GA) and epidermal thickness (ET) were determined by histological examination. Tensile tests were performed at a 5 mm/min crosshead speed up to the first opening along the incision. Immediate superficial closure with high CI values was found for the laser-irradiated incisions at the early phase of recovery. Clear welds without thermal damage were observed for the group irradiated at 1,070 nm. For the sutured group, the incisions remained unclosed for the first day, and openings through the incision were observed. At the end of the 21-day recovery period, no differences between experimental groups were observed in terms of the CI, GA and ET values. However, the tensile strength of the groups irradiated at 980 nm and 1,070 nm was found to be higher than that of the sutured incisions. The laser welding techniques were found to be reliable in terms of immediate and mechanically strong closure compared with suturing. Of them, 1,070 nm laser welding yielded noticeably stronger bonds, with minimal scarring at the end of the 21-days of recovery.

Modulated and continuous-wave operations of low-power thulium (Tm:YAP) laser in tissue welding

Our aim is to explore the welding capabilities of a thulium (Tm:YAP) laser in modulated and continuous-wave (CW) modes of operation. The Tm:YAP laser system developed for this study includes a Tm:YAP laser resonator, diode laser driver, water chiller, modulation controller unit, and acquisition/control software. Full-thickness incisions on Wistar rat skin were welded by the Tm:YAP laser system at 100 mW and 5 s in both modulated and CW modes of operation (34.66 Wcm(2)). The skin samples were examined during a 21-day healing period by histology and tensile tests. The results were compared with the samples closed by conventional suture technique. For the laser groups, immediate closure at the surface layers of the incisions was observed. Full closures were observed for both modulated and CW modes of operation at day 4. The tensile forces for both modulated and CW modes of operation were found to be significantly higher than the values found by conventional suture technique. The 1980-nm Tm:YAP laser system operating in both modulated and CW modes maximizes the therapeutic effect while minimizing undesired side effects of laser tissue welding. Hence, it is a potentially important alternative tool to the conventional suturing technique.

Systematic evaluations of skin damage irradiated by an erbium:YAG laser: histopathologic analysis, proteomic profiles, and cellular response

BACKGROUND

The erbium:yttrium-aluminum-garnet (Er:YAG) laser is used for surgical resurfacing. It has ablative properties with water as its main chromophore.

OBJECTIVE

This study attempted to establish the cutaneous effect and cellular response to Er:YAG laser irradiation using different fluences (7.5 and 15 J/cm(2)).

METHODS

Female nude mouse was used as the animal model in the study. Physiological parameters were examined and histology was evaluated at 4, 24 and 96 h after laser exposure. A proteomic analysis and immunoblotting were also used to determine the mechanisms of the laser's effect on the skin.

RESULTS

Both fluences were associated with a significant increase in transepidermal water loss (TEWL), erythema (a*), and the skin pH at 4 and 24h. In contrast, at 96 h, the levels of these parameters had generally decreased to the baseline. The histology examined by light microscopy and transmission electron microscopy (TEM) showed vacuolization, hydropic degeneration and epidermal necrosis of laser-irradiated skin. The higher fluence (15 J/cm(2)) exhibited more-severe disruption of the skin. Bulous and scarring were observed in skin treated with the higher fluence during the recovery period. p53 and p21 proteins were significantly activated in skin following exposure to the laser. However, proliferating cell nuclear antigen and cytokeratin expressions were downregulated by the low fluence (7.5 J/cm(2)).

CONCLUSION

Both proliferation and apoptosis occurred when the laser-irradiated the skin.

Optical, thermal, and electrical monitoring of radio-frequency tissue modification

Radio-frequency (rf) tissue fusion involves the sealing of tissue between two electrodes delivering rf currents. Applications include small bowel fusion following anastomosis. The mechanism of adhesion is poorly understood, but one hypothesis is that rf modification is correlated to thermal damage and dehydration. A multimodal monitoring system capable of acquiring tissue temperature, electrical impedance, and optical transmittance at 1325-nm wavelength during rf delivery by a modified Ligasure fusion tool is presented. Measurements carried out on single layers of ex vivo porcine small bowel tissue heated at approximately 500-kHz frequency are correlated with observation of water evaporation and histological studies on full seals. It is shown that the induced current generates a rapid quasilinear rise of temperature until the boiling point of water, that changes in tissue transmittance occur before impedance control is possible, and that a decrease in transmission occurs at typical denaturation temperatures. Experimental results are compared with a biophysical model for tissue temperature and a rate equation model for thermal damage.