Mathematical modeling of laser lipolysis

Measurements of hair temperature avalanche effect with alexandrite and Nd:YAG hair removal lasers

BACKGROUND AND OBJECTIVES

In this study, we investigate the photothermal response of human hair using a pulsed laser source employed in the hair removal treatment. The purpose is to understand the dynamics behind the most common clinical practice to better define the salient features that may contribute to the efficiency of the process.

STUDY DESIGN/MATERIALS AND METHODS

Temperature changes of hair samples (dark brown color) from a human scalp (skin type Fitpatrick II) were measured by a thermal camera following irradiation with single and multiple neodymium: yttrium-aluminum-garnet (Nd:YAG) (1064 nm) and alexandrite (755 nm) laser pulses. Particularly, the hair was treated with an individual laser pulse of a sufficiently high fluence, or with a series of lower fluence laser pulses. We investigated the temperature increase in a broad range of fluence and number of pulses. From the data analysis we extrapolated important parameters such as thermal gain and threshold fluence that can be used for determining optimal parameters for the hair removal procedure. Our experimental investigations and hypothesis were supported by a numerical simulation of the light-matter interaction in a skin-hair model, and by optical transmittance measurements of the irradiated hair.

RESULTS

An enhancement of the temperature response of the irradiated hair, that deviates from the linear behavior, is observed when hair is subjected to an individual laser pulse of a sufficiently high fluence or to a series of lower fluence laser pulses. Here, we defined the nonlinear and rapid temperature built-up as an avalanche effect. We estimated the threshold fluence at which this process takes place to be at 10 and 2.5 J/cm² for 1064 and 755 nm laser wavelengths, respectively. The thermal gain expressed by the degree of the deviation from the linear behavior can be higher than 2 when low laser fluence and multiple laser pulses are applied (n = 50). The comparison of the calculated gain for the two different laser wavelengths and the number of pulses reveals a much higher efficiency when low fluence and multiple pulses are delivered. The avalanche effect manifests when the hair temperature exceeds 45°C. The enhanced temperature increase during the subsequent delivery of laser pulses could be ascribed to the temperature-induced changes in the hair's structural properties. Simulations of the hair temperature under Nd:YAG and alexandrite irradiation indicate that the avalanche phenomenon observed in the hair suspended in air may apply also to the hair located within the skin matrix. Namely, for the same fluence, similar temperature increase was obtained also for the hair located within the skin.

CONCLUSION

The observed "avalanche" effect may contribute to the reported clinical efficacy of laser hair removal and may at least partially explain the observed efficacy of the brushing hair removal procedures where laser fluence is usually low. The repeated irradiation during the brushing procedure may lead to an avalanche-like gradual increase of the hair's thermal response resulting in sufficiently high final hair temperatures as required for effective hair reduction.

Development of a numerical multi-layer model of skin subjected to pulsed laser irradiation to optimise thermal stimulation in photorejuvenation procedure

BACKGROUND AND OBJECTIVE

This paper presents the development of a 3D physics-based numerical model of skin capable of representing the laser-skin photo-thermal interactions occurring in skin photorejuvenation treatment procedures. The aim of this model was to provide a rational and quantitative basis to control and predict temperature distribution within the layered structure of skin. Ultimately, this mathematical and numerical modelling platform will guide the design of an automatic robotic controller to precisely regulate skin temperature at desired depths and for specific durations.

METHODS

The Pennes bioheat equation was used to account for heat transfer in a 3D multi-layer model of skin. The effects of blood perfusion, skin pigmentation and various convection conditions are also incorporated in the proposed model. The photo-thermal effect due to pulsed laser light on skin is computed using light diffusion theory. The physics-based constitutive model was numerically implemented using a combination of finite volume and finite difference techniques. Direct sensitivity routines were also implemented to assess the influence of constitutive parameters on temperature. A stability analysis of the numerical model was conducted.

RESULTS

Finally, the numerical model was exploited to assess its ability to predict temperature distribution and thermal damage via a multi-parametric study which accounted for a wide array of biophysical parameters such as light coefficients of absorption for individual skin layers and melanin levels (correlated with ethnicity). It was shown how critical is the link between melanin content, laser light characteristics and potential thermal damage to skin.

CONCLUSIONS

The developed photo-thermal model of skin-laser interactions paves the way for the design of an automated simulation-driven photorejuvenation robot, thus alleviating the need for inconsistent and error-prone human operators.

1470-nm Radial fiber-assisted liposuction for body contouring and facial fat grafting

Background

Laser‐assisted liposuction using 1470‐nm radial fiber emits light energy preferentially absorbed by water, yielding a rapid and localized contouring and tightening effect, with minimal scarring. When collected under appropriate conditions, extracted fat samples can be exploited as autologous filling material in liposculpturing procedures.

Objectives

To assess the 6‐month contouring efficacy of 1470 radial fiber‐assisted liposuction and the volumetric enhancement effect of the harvested tissue in facial fat grafting.

Methods

Twenty subjects underwent liposuction (BeautiFill, Alma Lasers, Inc.) of lower abdominal or outer thigh fat. In seven subjects, harvested samples were grafted into facial regions. Treatment safety, body weight, blinded evaluator‐assessed aesthetic improvements, and subject‐rated satisfaction were monitored for 6 months. Abdominal and facial fat thickness were assessed by magnetic resonance imaging (n = 5) within 3 months of treatment.

Results

One‐month posttreatment, most subjects ranked improvements good/excellent (88%) and skin tightening satisfactory/very satisfactory (92%), with >70% of subjects providing similar scores 6‐month posttreatment. Blinded evaluators noted improved/very much improved aesthetic appearance (87%). Harvested tissue injected as a facial filler (21.0 ± 5.2 ml) led to a 0.63 ± 0.12 mm increase in facial fat thickness, observed by MRI, within 3 months. Six months postfilling, the majority of subjects (83%) were satisfied with the outcome. All procedures were well‐tolerated.

Conclusions

A single 1470 nm radial fiber‐assisted abdominal and thigh liposuction session provided for effective and durable reduction of adipose tissue deposits, with appreciable skin tightening and aesthetic improvements. The gentle harvesting method yielded viable filler material, which was well‐retained in facial regions for up to 6 months.

Towards personalized and versatile monitoring of temperature fields within heterogeneous tissues during laser therapies

Advancements in medical laser technology have paved the way for its widespread acceptance in a variety of treatments and procedures. Selectively targeting particular tissue structures with minimally invasive procedures limits the damage to surrounding tissue and allows for reduced post-procedural downtime. In many treatments that are hyperthermia-based, the efficiency depends on the achieved temperature within the targeted tissues. Current approaches for monitoring subdermal temperature distributions are either invasive, complex, or offer inadequate spatial resolution. Numerical studies are often therapy-tailored and source tissue parameters from the literature, lacking versatility and a tissue-specific approach. Here, we show a protocol that estimates the temperature distribution within the tissue based on a thermographic recording of its surface temperature evolution. It couples a time-dependent matching algorithm and thermal-diffusion-based model, while recognizing tissue-specific characteristics yielded by a fast calibration process. The protocol was employed during hyperthermic laser treatment performed ex-vivo on a heterogeneous porcine tissue, and in-vivo on a human subject. In both cases the calibrated thermal parameters correlate with the range of values reported by other studies. The matching algorithm sufficiently reproduced the temperature dynamics of heterogeneous tissue. The estimated temperature distributions within ex-vivo tissue were validated by simultaneous reference measurements, and the ones estimated in-vivo reveal a distribution trend that correlates well with similar studies. The presented method is versatile, supported by the protocol for tissue-specific tailoring, and can readily be implemented for temperature monitoring of various hyperthermia-based procedures by means of recording the surface temperature evolution with a miniature thermal camera implemented within a handheld laser scanner or similar.

Non-contact monitoring of the depth temperature profile for medical laser scanning technologies

Medical treatments such as high-intensity focused ultrasound, hyperthermic laser lipolysis or radiofrequency are employed as a minimally invasive alternatives for targeted tissue therapies. The increased temperature of the tissue triggers various thermal effects and leads to an unavoidable damage. As targeted tissues are generally located below the surface, various approaches are utilized to prevent skin layers from overheating and irreparable thermal damages. These procedures are often accompanied by cooling systems and protective layers accounting for a non-trivial detection of the subsurface temperature peak. Here, we show a temperature peak estimation method based on infrared thermography recording of the surface temperature evolution coupled with a thermal-diffusion-based model and a time-dependent data matching algorithm. The performance of the newly developed method was further showcased by employing hyperthermic laser lipolysis on an ex-vivo porcine fat tissue. Deviations of the estimated peak temperature remained below 1 °C, as validated by simultaneous measurement of depth temperature field within the tissue. Reconstruction of the depth profile shows a good reproducibility of the real temperature distribution with a small deviation of the peak temperature position. A thermal camera in combination with the time-dependent matching bears the scope for non-contact monitoring of the depth temperature profile as fast as 30 s. The latest demand for miniaturization of thermal cameras provides the possibility to embed the model in portable thermal scanners or medical laser technologies for improving safety and efficiency.

Temperature Depth Profiles Induced in Human Skin In Vivo Using Pulsed 975 nm Irradiation

BACKGROUND AND OBJECTIVES

The aim of this study was to determine the temperature depth profiles induced in human skin in vivo by using a pulsed 975 nm diode laser (with 5 ms pulse duration) and compare them with those induced by the more common 532 nm (KTP) and 1,064 nm (Nd:YAG) lasers. Quantitative assessment of the energy deposition characteristics in human skin at 975 nm should help design of safe and effective treatment protocols when using such lasers.

STUDY DESIGN/MATERIALS AND METHODS

Temperature depth profiles induced in the human skin by the three lasers were determined using pulsed photothermal radiometry (PPTR). This technique involves time-resolved measurement of mid-infrared emission from the irradiated test site and reconstruction of the laser-induced temperature profiles using an earlier developed optimization algorithm. Measurements were performed on volar sides of the forearms in seven volunteers with healthy skin. At irradiation spot diameters of 3-4 mm, the radiant exposures were 0.24, 0.36, and 5.7 J/cm² for the 975, 532, and 1,064 nm lasers, respectively.

RESULTS

Upon normalization to the same radiant exposure of 1 J/cm ² , the assessed maximum temperature rise in the epidermis averaged 0.8 °C for the 975 nm laser, 7.4 °C for the 532 nm, and 0.6 °C for the 1,064 nm laser. The characteristic subsurface depth to which 50% of the absorbed laser energy was deposited was on average 0.31 mm at 975 nm irradiation, and slightly deeper at 1,064 nm, and 0.15 mm at 532 nm. The experimentally obtained relations were reproduced in a dedicated numerical simulation.

CONCLUSIONS

The assessed energy deposition characteristics show that the pulsed 975 nm diode laser is very suitable for controlled heating of the upper dermis as required, for example, for nonablative skin rejuvenation. The risks of nonselective overheating of the epidermis and subcutis are significantly reduced in comparison with irradiation at 532 and 1,064 nm, respectively. Lasers Surg. Med. © 2019 Wiley Periodicals, Inc.

Adipose tissue, fillers, and skin tightening

The role of adipose tissue has long been underestimated in esthetic dermatology. With the development of liposculpture and lipolysis, subcutaneous adipose tissue has gained an increasing interest. Harvested tissue has been used for lipofilling. In recent years, a better understanding of adipocyte physiology and its role in aging opened a new road for targeted treatments. Subcutaneous adipose tissue is no longer an innocent bystander in the combat of aging and the correction in esthetics. Adipose tissue is of importance for metabolic function and thermoregulation. Adipose tissue is involved in inflammation. Adipose tissue is heterogeneous in sense of function, color and size of adipocytes. The tissue is an important source of somatic stem cells.

Does treadmill walking with near-infrared light applied to the abdominal area reduce local adiposity and body weight?

[Purpose] The purpose of this study was to determine the effect on local fat deposition and body weight of wearing a near-infrared light belt around the abdomen. [Subjects and Methods] Twenty-eight obese female subjects participated in this experiment. For measurement of body composition, an impedance-style body fat analyzer was used. The experimental group performed treadmill walking 3 times per week for 12 weeks while wearing an activated near-infrared belt around the abdomen. The near-infrared belt was composed of light-emitting diodes having wavelengths of 630 nm, 830 nm, 880 nm, and 956 nm. [Results] The analysis of abdominal circumference indicated that the abdominal circumference of the experimental group was reduced in post-test measurements compared to pre-test. [Conclusion] This investigation showed significant reductions in abdominal circumference, abdominal fat percentage, fat mass, and body-mass index for the experimental compared to the control group, suggesting that changes in body composition can be enhanced when near-infrared radiation is applied to the abdomen during walking.

Body Contouring and Skin Tightening Using a Unique Novel Multisource Radiofrequency Energy Delivery Method

Objective: The objective of this study was to examine the efficacy and safety of the latest multisource radiofrequency handpiece, specially designed for body area skin treatments. The new handpiece features six concentric electrodes, each connected to an independently controlled radiofrequency generator. Design and settings: This was an international multicenter study across two sites. Twenty-five patients were enrolled into the study. Patients underwent at least five sessions of body skin tightening and circumference reduction. The first four sessions were held at one-week intervals and the other 1 to 4 remaining sessions, at two-week intervals. Participants: Twenty-five patients (23 women and 2 men). Measurements: Overall change was graded by the physicians using the global aesthetic improvement scale. Patients were asked to complete satisfaction questionnaires at the end of the treatment sessions. Images were taken prior to the treatments, before every treatment session, and at the follow-up visit. Results: No adverse events were reported as a result of the treatment. Measured body weight of the patients, as monitored during the study period, was stable (±2kg). Ninety-two percent of the patients were pleased with the results and finished all the treatment sessions. Twenty-four patients (96%) saw an improvement in body shape. Ninety-two percent of the patients would recommend the treatment to others. Overall change graded by the physician by the global aesthetic improvement scale provided the following results: 44 percent of the patients had more than 75-percent improvement, 32 percent of the patients between 50- to 75-percent improvement, 20 percent of the patients had between 25- to 50-percent improvement and only four percent had less than 25-percent improvement. Conclusion: The authors' data show that the handpiece examined provides high efficacy in skin tightening and body contouring after 5 to 8 painless treatments. Patient subjective questionnaires show very high satisfaction rates.

Ex vivo laser lipolysis assisted with radially diffusing optical applicator

Laser-assisted lipolysis has been implemented to reduce body fat in light of thermal interactions with adipose tissue. However, using a flat fiber with high irradiance often needs rapid cannula movements and even undesirable thermal injury due to direct tissue contact. The aim of the current study was to explore the feasibility of a radially diffusing optical applicator to liquefy the adipose tissue for effective laser lipolysis. The proposed diffuser was evaluated with a flat fiber in terms of temperature elevation and tissue liquefaction after laser lipolysis with a 980-nm wavelength. Given the same power (20 W), the diffusing applicator generated a 30% slower temperature increase with a 25% lower maximum temperature (84±3.2°C in 1 min; p<0.001) in the tissue, compared with the flat fiber. Under the equivalent temperature development, the diffuser induced up to fivefold larger area of the adipose liquefaction due to radial light emission than the flat fiber. Ex vivo tissue tests for 5-min irradiation demonstrated that the diffuser (1.24±0.15  g) liquefied 66% more adipose tissue than the flat fiber (0.75±0.05  g). The proposed diffusing applicator can be a feasible therapeutic device for laser lipolysis due to low temperature development and wide coverage of thermal treatment.

The 975 nm Diode Laser in the Photothermal Treatment of the Aging and Sagging Face and Neck

OBJECTIVE

The purpose of this study was to investigate the use of a 975 nm diode laser for skin tightening.

BACKGROUND DATA

The photothermal effect of laser irradiation on the hypodermis causes retraction of superficial and deep skin layers by the heating of fibrous septa. New devices have been developed for repairing deformities in the cervicofacial region associated with aging and skin laxity.

MATERIALS AND METHODS

This retrospective, cross-sectional study included the medical records of 17 patients who had undergone photothermal laser therapy to correct deformities in the cervicofacial region between June 2013 and February 2015. An energy dose of 3 kJ per 100 cm(2) skin area was used as a safety parameter to calculate the optimal cumulative energy for the treated areas. Four cervicofacial lines were measured preoperatively (baseline), immediately after treatment, and 3 months post-treatment with a caliper. Measurements were compared using the Wilcoxon test at a significance level of 0.05 (p < 0.05).

RESULTS

A significant skin tightening was observed in all patients 3 months after the procedure. Mean length reductions found in the cervicofacial lines L1, L2, L3, and L4 at the 3-month follow-up were 0.9, 1.18, 1.32, and 1.27 cm, respectively.

CONCLUSIONS

The use of a 975 nm diode laser resulted in skin tightening.

Laser-assisted lipolysis for arm contouring in Teimourian grades III and IV: A prospective study involving 22 patients

BACKGROUND

Upper arm deformities secondary to weight loss or senile elastosis have led to an increased demand for aesthetic contouring procedures.

OBJECTIVE

To objectively assess whether, in Teimourian high-grade upper arm remodelling, laser-assisted lypolysis (LAL) alone could result in patient satisfaction.

METHODS

Between 2012 and 2013, 22 patients were treated for excessive upper arm fat (Teimourian grade III and IV) solely with LAL. The laser used in the present study was a 1470 nm diode laser (Alma Lasers, Israel) with the following parameters: continuous mode, 15 W power and transmission through a 600 μm optical fibre. Previous mathematical modelling suggested that 0.1 kJ was required to destroy 1 mL of fat. Patients were asked to complete a satisfaction questionnaire. The arm circumference was measured pre- and postoperatively. Treatment parameters, adverse effects and outcomes were recorded.

RESULTS

Pain during the anesthesia and discomfort after the procedure were minimal. Complications included ecchymoses and prolonged edema. The mean (± SD) arm circumference decreased 5.5±1.0 cm in the right arm (P<0.01) and 5.2±1.1 cm in the left arm (P<0.01) in grade III patients and 4.9±1.1 cm in the right arm (P<0.01) and 4.9±1.1 cm in the left arm (P<0.01) in grade IV patients. Although the circumference of both arms significantly decreased in grade III and grade IV patients, the skin tightening remained incomplete. Overall, the average opinion of treatment was poor for both patients and investigators. Of the 22 patients, only nine (41%) would recommend this treatment.

CONCLUSION

LAL for upper arm remodelling is not sufficient to ensure full skin tightening for patients with Teimourian grades III and IV upper arm deformities. A complementary surgery is mandatory for grades III and IV.

Impact of heat stress on germinal vesicle breakdown and lipolytic changes during in vitro maturation of bovine oocytes

Two studies were conducted with the overarching goal of determining the extent to which lipolytic changes relate to germinal vesicle breakdown (GVBD) in bovine oocytes matured under thermoneutral or hyperthermic conditions. To this end, cumulus-oocyte complexes underwent in vitro maturation for 0, 2, 4, 6 or 24 h at 38.5 (first study) or 38.5 and 41.0 C (second study; heat stress applied up through first 12 h only, then shifted to 38.5 C). Independent of maturation temperature, triglyceride and phospholipid content decreased markedly by 2 h of in vitro maturation (hIVM; P < 0.0005). Content was lowest at 24 hIVM with no detectable impact of heat stress when exposure occurred during first 12 hIVM. Germinal vesicle breakdown occurred earlier in oocytes experiencing heat stress with effects observed as soon as 4 hIVM (P < 0.0001). Germinal vesicle breakdown was associated with lipolytic changes (R² = 0.2123 and P = 0.0030 for triglyceride content; R² = 0.2243 and P = 0.0026 for phospholipid content). ATP content at 24 hIVM was higher in oocytes experiencing heat stress (P = 0.0082). In summary, GVBD occurs sooner in heat-stressed oocytes. Although marked decreases in triglyceride and phospholipid content were noted as early as 2 hIVM and preceded GVBD, lipolytic changes such as these are not likely serving as an initial driver of GVBD in heat-stressed oocytes because changes occurred similarly in oocytes matured at thermoneutral conditions.

Laser-assisted lipolysis for arm contouring in Teimourian grades I and II: a prospective study of 45 patients

Upper arm deformities secondary to weight loss or senile elastosis have led to an increased demand for aesthetic contouring procedures. We conducted this study to objectively assess if, in Teimourian low-grade upper arm remodelling, one session of laser-assisted lypolisis (LAL) could result in full patient satisfaction. Between 2011 and 2013, 45 patients were treated for unsightly fat arm Teimourian grade I (15 patients), grade IIa (15 patients) and grade IIb (15 patients) with one session of LAL. The laser used in this study was a 1470-nm diode laser (Alma Lasers, Cesarea, Israel) with the following parameters: continuous mode, 15 W power and transmission through a 600-μm optical fibre. Previous mathematical modelling suggested that 0.1 kJ was required in order to destroy 1 ml of fat. Treatment parameters and adverse effects were recorded.The arm circumference and skin pinch measurements were assessed pre and postoperatively. Patients were asked to file a satisfaction questionnaire. Pain during the anaesthesia and discomfort after the procedure were minimal. Complications included prolonged oedema in 11 patients. The average arm circumference decreased by 4.9 ± 0.4 cm in the right arm (p < 0.01) and 4.7 ± 0.5 cm in the left arm (p < 0.01) in grade I patients, 5.5 ± 0.6 cm in the right arm (p < 0.01) and 5.2 ± 0.5 cm in the left arm (p < 0.01) in grade IIa patients and 5.4 ± 0.5 cm in the right arm (p < 0.01) and 5.3 ± 0.5 cm in the left arm (p < 0.01) in grade IIB patients. The skin tightening effect was confirmed by the reduction of the skin calliper measurements in all three groups. Overall mean opinion of treatment was high for both patients and investigators. Of the 45 patients, all but one would recommend this treatment. A single session of LAL in upper arm remodelling for Teimourian grades I to IIb is a safe and reproducible technique. The procedure allows reduction in the amount of adipose deposits while providing full skin tightening.

Study of Interaction of Laser with Tissue Using Monte Carlo Method for 1064nm Neodymium-Doped Yttrium Aluminium Garnet (Nd:YAG) Laser

INTRODUCTION

Liposuction using laser is now one of the most common cosmetic surgery. This new method has minimized the disadvantages of the conventional liposuction including blood loss, skin laxity and long recovery time. Benefits of the new liposuction methods which include less trauma, bleeding and skin tightening prove the superiority of these methods over the traditional mechanical methods. Interaction of laser with fat tissue has the vital role in the development of these new procedures because this interaction simultaneously results in retraction of skin layers and coagulation of small blood vessels so skin tightening and less bleeding is achieved.

METHOD

Laser lipolysis uses a laser fiber inserted inside a metal cannula of 1 mm delivering the laser radiation directly to the target tissue. Laser lipolysis has a wavelength dependent mechanism, tissue heating and therefor thermal effects are achieved through absorption of radiation by the target tissue cells, causing their temperature to rise and their volumes to expand. We used Monte Carlo (MC) method to simulate the photons propagation within the tissue. This method simulates physical variables by random sampling of their probability distribution. We also simulated temperature rise and tissue heating using Comsol Multiphysics software.

CONCLUSION

Because optimum and safe laser lipolysis operation highly depends on optical characteristics of both tissue and laser radiation such as laser fluence, laser power and etc. having physical understanding of these procedures is of vital importance. In this study we aim to evaluate the effects of these important parameters.

RESULTS

Findings of our simulation prove that 1064 nm Neodymium-Doped Yttrium Aluminium Garnet (Nd:YAG) has good penetration depth into fat tissue and can reach inside the deeper layers of fat tissue. We see that this wavelength also resulted in good temperature rise; after irradiation of fat tissue with this wavelength we observed that tissue heated in permitted values (50-65°C), this is why this wavelength is widely used in laser lipolysis operations.

Development of a computational simulation tool to design a protocol for treating prostate tumours using transurethral laser photothermal therapy

OBJECTIVES

The objective of this study was to design laser treatment protocols to induce sufficient thermal damage to a tumour embedded in a prostate model, while protecting the surrounding healthy tissue.

METHODS

A computational Monte Carlo simulation algorithm of light transport in a spherical prostatic tumour containing gold nanorods was developed to determine laser energy deposition. The laser energy absorption was then used to simulate temperature elevations in the tumour embedded in an elliptical human prostate model. The Arrhenius integral was coupled with the heat transfer model to identify heating protocols to induce 100% damage to the tumour, while resulting in less than 5% damage to the surrounding sensitive prostatic tissue.

RESULTS

Heating time to achieve 100% damage to the tumour was identified to be approximately 630 s when using a laser irradiance of 7 W/cm2 incident on the prostatic urethral surface. Parametric studies were conducted to show how the local blood perfusion rate and urethral surface cooling affect the heating time to achieve the same thermal dosage. The heating time was shorter when cooling at the urethra was not applied and/or with heat-induced vasculature damage. The identified treatment protocols were acceptable since the calculated percentages of the damaged healthy tissue volume to the healthy prostatic volume were approximately 2%, less than the threshold of 5%. The approach and results from this study can be used to design individualised treatment protocols for patients suffering from prostatic cancer.

Laser assisted lipolysis for neck and submental remodeling in Rohrich type I to III aging neck: a prospective study in 30 patients

BACKGROUND

Since the first studies by Apfelberg in 1994 and the mathematical model by Mordon in 2004, laser lipolysis (LAL) has been on the rise. Laser lipolysis has the advantages of reduced operator fatigue, excellent patient tolerance, quick recovery time, as well as the additional benefit of dermal tightening. This article reports our experience with laser-assisted lipolysis (LAL) in submental and neck remodelling.

METHODS

Between June 2010 and January 2013, a prospective study was performed on 30 patients treated for Rohrich type I to III aging neck, with LAL. The laser used in this study was a 980 nm diode laser (Quanta system, spa model D-plus, Solbate Olona (VA), Italy). Laser energy was transmitted through a 600 μm optical fiber and delivered in a continuous mode 15 W power. Previous mathematical modelling suggested that 0.1 kJ was required in order to destroy 1 ml of fat. Patients were asked to fill out a satisfaction questionnaire. The cervicomental angle was measured 6 months post-operatively and compared with the preoperative values.

RESULTS

Other than three patients who developed mild hyperpigmentation that disappeared after 4 months, there were no complications in the series. Pain during the anaesthesia and discomfort after the procedure were minimal. The time taken to return to normal activities was 3.2 ± 1 days. All patients would strongly recommend this treatment. Overall satisfaction was high with both patients and investigators and was validated by decrease in cervicomental angle demonstrating a systematic decrease in fat thickness and improved skin tightening.

CONCLUSION

LAL is a safe and reproducible technique for remodeling in Rohrich type I to III aging neck. The procedure allows for a reduction in the amount of adipose deposits while providing concurrent skin contraction.

Optical-thermal light-tissue interactions during photoacoustic breast imaging

Light-tissue interactions during photoacoustic imaging, including dynamic heat transfer processes in and around vascular structures, are not well established. A three-dimensional, transient, optical-thermal computational model was used to simulate energy deposition, temperature distributions and thermal damage in breast tissue during exposure to pulsed laser trains at 800 and 1064 nm. Rapid and repetitive temperature increases and thermal relaxation led to superpositioning effects that were highly dependent on vessel diameter and depth. For a ten second exposure at established safety limits, the maximum single-pulse and total temperature rise levels were 0.2°C and 5.8°C, respectively. No significant thermal damage was predicted. The impact of tissue optical properties, surface boundary condition and irradiation wavelength on peak temperature location and temperature evolution with time are discussed.

Diffuse optical tomography: image reconstruction and verification

INTRODUCTION

In this study, we intend to use diffuse optical Tomography (DOT) as a noninvasive, safe and low cost technique that can be considered as a functional imaging method and mention the importance of image reconstruction in accuracy and procession of image. One of the most important and fastest methods in image reconstruction is the boundary element method (BEM). This method is introduced and employed in our works.

METHOD

Generally, to image a biological tissue we must obtain its optical properties. In order to reach this goal we benefit from diffusion equation because tissue is highly scattering medium. Diffusion equation is solved by boundary element equation (BEM) in our research. First, we assume a double layer phantom with different scattering and absorption coefficients to simulate and verify precession and accuracy of image reconstruction by BEM. Light absorption can be affected by volume fraction of blood in skin. For a specific skin species the volume fraction is calculated and then the results are compared with the reconstructed values obtained by BEM. Since the depth of tissue is important in light absorption a two layer phantom with known values is made and the depths of layers are reconstructed by BEM then they are compared with the expected values. A homogenous phantom with known scattering and absorption coefficients was made and then these coefficients were reconstructed by BEM. Finally, an inhomogeneous phantom (phantom with defect) whose defect was in a known position was made and the absorption and scattering coefficients were reconstructed and compared with real values.

RESULTS

Comparison between real or simulated values and reconstructed values of scattering and absorption coefficients, volume fraction of blood and thickness of phantom layers by BEM shows maximum errors of 24%, 7% and 35%, respectively.

CONCLUSION

Comparison between BEM data and real or simulated values shows an acceptabl eagreement. Consequently, we can rely on BEM as a beneficial method in diffuse optical tomography image reconstruction.

Temperature profiles of 980- and 1,470-nm endovenous laser ablation, endovenous radiofrequency ablation and endovenous steam ablation

Endovenous thermal ablation (EVTA) techniques are very effective for the treatment of varicose veins, but their exact working mechanism is still not well documented. The lack of knowledge of mechanistic properties has led to a variety of EVTA protocols and a commercially driven dissemination of new or modified techniques without robust scientific evidence. The aim of this study is to compare temperature profiles of 980-and 1,470-nm endovenous laser ablation (EVLA), segmental radiofrequency ablation (RFA), and endovenous steam ablation (EVSA). In an experimental setting, temperature measurements were performed using thermocouples; raw potato was used to mimic a vein wall. Two laser wavelengths (980 and 1,470 nm) were used with tulip-tip fibers and 1,470 nm also with a radial-emitting fiber. Different powers and pullback speeds were used to achieve fluences of 30, 60, and 90 J/cm. For segmental RFA, 1 cycle of 20 s was analyzed. EVSA was performed with two and three pulses of steam per centimeter. Maximum temperature increase, time span of relevant temperature increase, and area under the curve of the time of relevant temperature increase were measured. In all EVLA settings, temperatures increased and decreased rapidly. High fluence is associated with significantly higher temperatures and increased time span of temperature rise. Temperature profiles of 980- and 1,470-nm EVLA with tulip-tip fibers did not differ significantly. Radial EVLA showed significantly higher maximum temperatures than tulip-tip EVLA. EVSA resulted in mild peak temperatures for longer durations than EVLA. Maximum temperatures with three pulses per centimeter were significantly higher than with two pulses. RFA temperature rises were relatively mild, resulting in a plateau-shaped temperature profile, similar to EVSA. Temperature increase during EVLA is fast with a high-peak temperature for a short time, where EVSA and RFA have longer plateau phases and lower maximum temperatures.

Histological evaluation of dermal tissue remodeling with the 1444-nm neodymium:yttrium-aluminum-garnet laser in in vivo model

Laser lipolysis has a skin tightening effect by heating the deep dermis, in addition to the removal of fat tissues. The 1444-nm neodymium:yttrium-aluminum-garnet (Nd:YAG) laser has been expected to be more effective and safe for laser lipolysis, due to higher affinity to fat and water, than 1064-nm and 1320-nm wavelengths. The purpose of this study was to evaluate the skin tightening effect of the 1444-nm Nd:YAG laser through in vivo guinea pig models. The 1444-nm Nd:YAG laser was used to irradiate shaved dorsal skin of the guinea pigs and compared with controls (no power, only tunneling). Immediately, 1 week, 1 month and 3 months after laser administration, full-thickness skins were harvested and to evaluate dermal thickness, collagen organization, fibroblast proliferation, and intensity of elastic fibers and mucopolysaccharides, using hematoxylin-eosin, Masson-trichrome, Verhoeff's stain and Alcian blue stain. Dermal thickness showed an increase with time in all groups. In collagen organization, fibroblast proliferation, and intensity of elastic fibers and mucopolysaccharides, the treatment groups were higher than those of the control group, overall. Our study showed that the 1444-nm Nd:YAG laser appeared to be effective for the skin tightening effect in in vivo guinea pig models. The 1444-nm Nd:YAG laser can be used for skin tightening, as well as reduction of fat tissues.

Laser lipolysis using a 924- and 975-nm laser diode in the lower extremities

BACKGROUND

Laser technology provides the desired destruction of adipose tissue, hemostasis, and good skin retraction with a minimum of discomfort and a quick return to normal life for the patient. Here we present our experience with the use of laser-assisted liposuction (LAL) with a 924- and 975-nm laser diode and compare it with traditional liposuction alone.

METHODS

A total of 430 patients were reviewed for this study. Three hundred thirty patients were treated with the 924- and 975-nm laser diode for laser lipolysis and 100 patients were treated with traditional liposuction of the anterior and inner thigh, the knee, the calf, and the trochanter. Patients were assessed by means of ultrasound. Pictures were taken and the degree of satisfaction was assessed. All complications were recorded.

RESULTS

A total of 521 laser lipolysis procedures were performed at different areas: anterior thigh (86), inner thigh (122), trochanter (204), knee (67), and calf (42). The mean energy was area-dependent and evaluated in kJ: anterior thigh (15), inner thigh (14), trochanter (22), knee (5), and calf (4.5). The mean reduction of subcutaneous tissue with LAL in the anterior part of the thigh, the inner thigh, the calf, the knees, and the trochanter was 1.45, 1.9, 1.15, 1.2, and 3.6 cm, respectively. One hundred traditional liposuction procedures were performed for different areas: anterior thigh (27), inner thigh (38), trochanter (72), knee (21), and calf (12). The mean reduction of subcutaneous tissue in the anterior part of the thigh, the inner thigh, the calf, the knees, and the trochanter was 1.2, 1.6, 0.9, 0.6, and 3.2 cm, respectively. All patients who underwent LAL had superior satisfaction compared to those who had liposuction alone.

CONCLUSION

Laser lipolysis with 924- and 975-nm diodes is adequate treatment for removal of adipose deposits and to obtain aesthetically good skin results, with a minimum of recovery time and high patient satisfaction.

LEVEL OF EVIDENCE IV

This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

[Laser-assisted lipolysis for gynecomastia: safe and effective skin retraction]

OBJECTIVES

To evaluate efficacy of laser lipolysis in the treatment of gynecomastia to correct breast volume, flaccidity and excess skin without its excision.

METHODS

Prospectively, 32 patients with gynecomastia under tumescent anaesthesia and sedation underwent laser lipolysis with 980 nm diode laser, 15W continuous emission and 8 to 12 kJ energy per breast. Externally cold air was used to protect the skin. No drainages were used but a compressive bandage. Patients evaluated results on a VAS scale. Two doctors evaluated results comparing before and 6 month after photographs and also measured the areola and chest diameter.

RESULTS

Twenty three patients considered results as Very Good, 7 Good and 2 Fair Cutaneous retraction of the areola was noticeable one month after the surgery and was maximum 6 months after. Evaluation by doctors was 26 Very Good, 5 Good and 1 Fair. There were no burns, ischemia or lesions in areolas or nipples.

CONCLUSION

Laser assisted liposuction is a simple and efficacious technique, barely traumatic and permits a rapid reincorporation to normal activities.

Numerical simulation of endovenous laser treatment of the incompetent great saphenous vein with external air cooling

Endovenous laser treatment (ELT) has been proposed as an alternative in the treatment of reflux of the great saphenous vein. Before the procedure, peri-saphenous subcutaneous tumescent saline solution infiltration is usually performed. However, diffusion of this tumescent fluid is rapidly observed and can potentially reduce the efficacy as a heat sink. External skin cooling with cold air was proposed as an alternative solution. The objective of this study is to compare endovenous laser treatment without and with air cooling by realistic numerical simulations. An optical-thermal damage model was formulated and implemented using finite element modeling. The general model simulated light distribution using the diffusion approximation of the transport theory, temperature rise using the bioheat equation, and laser-induced injury using the Arrhenius damage model. Parameters, used in clinical procedures, were considered: power, 15 W; pulse duration, 1 s; fiber pull back, 3-mm increments every second; cold air applied in continuous mode during ELT; and no tumescent anesthesia. Simulations were performed for vein locations at 5, 10, and 15 mm in depth, with and without air cooling. For a vein located at 15 mm in depth, no significant difference was observed with and without cooling. For a vein located at 10 mm in depth, surface temperature increase up to 45 °C is observed without cooling. For a vein located at 5 mm, without cooling, temperature increase leads to irreversible damage of dermis and epidermis. Conversely, with air cooling, surface temperature reaches a maximum of 38 °C in accordance with recordings performed on patients. ELT of the incompetent great saphenous vein with external air cooling system is a promising therapy technique. Use of cold air on the skin continuously flowing in the area of laser shot decreased significantly the heat extent and the thermal damage in the perivenous tissues and the skin.

New frontiers in laser surgery

The simultaneous advances in engineering, medicine, and molecular biology have accelerated the pace of introductions of new light-based technologies in dermatology. In this review, the authors examine recent advances in laser surgery as well as peer into the future of energy-based cutaneous medicine. The future landscape of dermatology will almost undoubtedly include (1) noninvasive imaging technologies and (2) improved "destructive" modalities based on real-time feedback from the skin surface.

Focal laser ablation of prostate cancer: definition, needs, and future

Current challenges and innovations in prostate cancer management concern the development of focal therapies that allow the treatment of only the cancer areas sparing the rest of the gland to minimize the potential morbidity. Among these techniques, focal laser ablation (FLA) appears as a potential candidate to reach the goal of focusing energy delivery on the identified targets. The aim of this study is to perform an up-to-date review of this new therapeutic modality. Relevant literature was identified using MEDLINE database with no language restrictions (entries: focal therapy, laser interstitial thermotherapy, prostate cancer, FLA) and by cross-referencing from previously identified studies. Precision, real-time monitoring, MRI compatibility, and low cost of integrated system are principal advantages of FLA. Feasibility and safety of this technique have been reported in phase I assays. FLA might eventually prove to be a middle ground between active surveillance and radical treatment. In conclusion, FLA may have found a role in the management of prostate cancer. However, further trials are required to demonstrate the oncologic effectiveness in the long term.

Ablation efficiency and relative thermal confinement measurements using wavelengths 1,064, 1,320, and 1,444 nm for laser-assisted lipolysis

Laser-assisted lipolysis is routinely used for contouring the body and the neck while modifications of the technique have recently been advocated for facial contouring. In this study, wavelength-dependence measurements of laser lipolysis effect were performed using different lasers at 1,064, 1,320, and 1,444 nm wavelengths that are currently used clinically. Fresh porcine skin with fatty tissue was used for the experiments with radiant exposure of 5–8 W with the same parameters (beam diameter = 600 μm, peak power = 200 mJ, and pulse rate = 40 Hz) for 1,064, 1,320 and 1,444 nm laser wavelengths. After laser irradiation, ablation crater depth and width and tissue mass loss were measured using spectral optical coherence tomography and a micro-analytical balance, respectively. In addition, thermal temporal monitoring was performed with a thermal imaging camera placed over ex vivo porcine fat tissue; temperature changes were recorded for each wavelength. This study demonstrated greatest ablation crater depth and width and mass removal in fatty tissue at the 1,444 nm wavelength followed by, in order, 1,320 and 1,064 nm. In the evaluation of heat distribution at different wavelengths, reduced heat diffusion was observed at 1,444 nm. The ablation efficiency was found to be dependent upon wavelength, and the 1,444 nm wavelength was found to provide both the highest efficiency for fatty tissue ablation and the greatest thermal confinement.

Evaluation of Tissue Tightening by the Subdermal Nd: YAG Laser-Assisted Liposuction Versus Liposuction Alone

BACKGROUND

Skin tightening is a desirable outcome for skin flaccidity.

OBJECTIVE

We evaluated the applicability, safety, capacity and intensity of skin tightening with the subdermal 1,064 nm Nd: YAG laser application to the upper arms, and compared the results with liposuction.

MATERIALS AND METHODS

Patients with lipodystrophy and mild-to-severe skin laxity of the arms were included (n=28). In half of patients, a single treatment with a subcutaneous laser and liposuction was performed, while the other 14 had a regular liposuction. Treatment parameters, adverse effects and photographic documentation were recorded.

RESULTS

Aesthetic improvement and skin retraction was superior by laser lipolysis. The procedure was well tolerated without significant complications.

CONCLUSIONS

The subdermal laser-assisted liposuction using a 1,064 nm Nd: YAG laser achieves improved skin tightening.

New clinical outcomes utilizing a 1064-nm Nd:YAG laser for lipolysis of the torso oblique region

OBJECTIVES

The safety and efficacy of a 1064-nm Nd:YAG laser (Cynosure, Westford, USA) utilizing a 300-microm optical fiber and a 1-mm diameter micro-cannula were evaluated as a treatment for reduction in the appearance or elimination of unwanted fat in the lower back/flanks ('love handles'). In addition, the use of the laser for tightening the skin and collagen regeneration in the area of lipolysis was assessed through biopsies.

METHODS

Ten subjects with unwanted flaccidity and fat deposits in the oblique region of the torso were enrolled in the study. Subjects underwent a single laser lipolysis treatment followed by aspiration of the treatment area. The total tumescence used, laser energy delivered, and tissue removed was recorded for each subject. All subjects had baseline photographs taken and their weight recorded prior to treatment. Pregnancy tests (if applicable) were performed prior to treatment as well. Three subjects had 4-mm biopsies taken at baseline and 6 months to evaluate collagen regeneration. Collagen and elastic tissue fibers were evaluated using special routine stains and histochemical stains designed to highlight these dermal components. Follow-up visits were conducted at 1 week, 1 month, 3 months and 6 months following treatment to evaluate side effects, weight loss and laxity. Additionally, patients kept an evaluation log for each of the first 7 days following treatment. At the 6-month conclusion, patient satisfaction was recorded.

RESULTS

Laser lipolysis procedures with subsequent aspiration were performed bilaterally on the flanks of 10 subjects. At 1-week post-treatment, 80% of the subjects demonstrated reduction in laxity. Similarly, 100% of patients showed visible skin improvement at 1 month, with 70% recording a score of 2 (good improvement). Three-month evaluations yielded one patient (10%) with a score of 3 (excellent improvement) and seven patients (70%) with a score of 2. Histology reports confirmed the visual clinical outcomes, describing thicker collagen bundles at 6 months, as well as coagulation of blood vessels and adipocytes. Side effects were mild and transient in nature, and the majority of discomfort, redness, bruising, swelling, and tingling experienced was resolved within 1 week post-procedure. The treatment was well tolerated and efficacious, with 90% of patients rating their results as good or excellent and 100% of patients reporting that they would recommend the procedure.

CONCLUSION

The use of the 1064-nm Nd:YAG laser with a 300-microm fiber demonstrated the ability to treat adipose tissue in the highly vascular flank area with favorable efficacy and safety. Patients exhibited a quick recovery time and excellent tolerance, as well as visually improved skin.

Discussion of laser-assisted liposuction

There has been a significant advancement in the use of lasers for body contouring over the past several years. This article will review the recent past and discuss the future of this trend.

INTRODUCTION

There is much confusion over the definition of procedures using lasers for lipolysis and liposuction. This review article discusses the definitions of suction-assisted liposuction, laser lipolysis, and laser-assisted liposuction in detail. The development of these procedures is then discussed and pertinent articles are reviewed.

MATERIALS AND METHODS

Pubmed and FDA.gov web sites were searched for published articles and FDA approved devices employing lasers for targeting fat for body contouring. This information along with the authors' personal experience was used to review and discuss this topic.

DISCUSSION

There is a specific difference between suction-assisted liposuction, laser-assisted liposuction, and laser lipolysis. This review article clarifies these definitions and highlights the recent articles employing lasers for minimally invasive fat reduction.

Laser lipolysis versus traditional liposuction for fat removal

Liposuction is second only to breast augmentation as the most commonly performed cosmetic procedure in the USA. Liposuction removes fat through very small skin incisions, with atraumatic, blunt-tipped cannulas. Simplicity, quality of results and relatively rare complications are but a few benefits that explain its success. Its main limitation is the minimal skin retraction achieved after the procedure. Laser lipolysis is based on a thermal effect. The laser can vaporize, melt tissues and coagulate blood vessels. More importantly, the laser stimulates the formation of collagen in the region, enhancing skin elasticity and promoting skin contraction in the treated areas. This review aims to describe traditional liposuction and laser lipolysis, and discusses the difference between the two techniques.