Effect of the Combination of Different Electrode Spacings and Power on Bipolar Radiofrequency Fat Dissolution: A Computational and Experimental Study

Accurate Temperature Reconstruction in Radiofrequency Ablation for Atherosclerotic Plaques Based on Inverse Heat Transfer Analysis

Radio frequency ablation has emerged as a widely accepted treatment for atherosclerotic plaques. However, monitoring the temperature field distribution in the blood vessel wall during this procedure presents challenges. This limitation increases the risk of endothelial cell damage and inflammatory responses, potentially leading to lumen restenosis. The aim of this study is to accurately reconstruct the transient temperature distribution by solving a stochastic heat transfer model with uncertain parameters using an inverse heat transfer algorithm and temperature measurement data. The nonlinear least squares optimization method, Levenberg-Marquardt (LM), was employed to solve the inverse heat transfer problem for parameter estimation. Then, to improve the convergence of the algorithm and reduce the computational resources, a method of parameter sensitivity analysis was proposed to select parameters mainly affecting the temperature field. Furthermore, the robustness and accuracy of the algorithm were verified by introducing random noise to the temperature measurements. Despite the high level of temperature measurement noise (ξ = 5%) and larger initial guess deviation, the parameter estimation results remained closely aligned with the actual values, with an overall ERMS consistently below 0.05. The absolute errors between the reconstruction temperature at the measurement points TC1, TC2, and TC3, and the actual temperature, remained within 0.33 °C, 2.4 °C, and 1.17 °C, respectively. The Levenberg-Marquardt algorithm employed in this study proficiently tackled the ill-posed issue of inversion process and obtained a strong consistency between the reconstructed temperature the actual temperature.

A novel electrode for reducing tissue thermal damage in radiofrequency-induced intestinal anastomosis

PURPOSE

This study aimed to design a novel electrode for reducing tissue thermal damage in radiofrequency-induced intestinal anastomosis.

MATERIAL AND METHODS

We developed and compared two electrodes (Ring electrode, and Plum electrode with reduced section of the middle fusion area by nearly 80% arising from novel structural design) by performing ex-vivo experiments and finite element analysis.

RESULTS

In contrast to the Ring electrode group, slightly higher mean strength is acquired with the tensile force and burst pressure results increasing from 9.7 ± 1.47 N, 84.0 ± 5.99 mmHg to 11.1 ± 1.71 N, 89.4 ± 6.60 mmHg, respectively, as well as a significant reduction in tissue thermal damage for the Plum electrode group, with compression pressure of 20 kPa, RF energy of 120 W and welding duration of 8 s applied to the target regions to achieve anastomosis. Besides, the novel structural design of the Plum electrode can counteract the tension generated by intestinal peristalsis and enhance the biomechanical strength of the anastomotic area. The histological observation showed that the fusion area of the two-layer intestinal tissue is tightly connected with decreased thickness.

CONCLUSION

The novel electrode (Plum electrode) could reduce tissue thermal damage in radiofrequency-induced intestinal anastomosis.

Effect of geometric parameters of electrodes on skin heating for the design of non-ablative radiofrequency device

BACKGROUND

Non-ablative radiofrequency (RF) has been widely used in clinical and at-home cosmetics devices. RF electrode geometry can influence the heat distribution in the tissue. This study analyzes the influence of geometric parameters of the electrode on the heat distribution in the layered tissue.

MATERIALS & METHODS

The finite element simulation of the electrothermal coupling field was performed to obtain the three-dimensional (3D) temperature distribution of the four-layer tissue. The electrode geometric parameters including the inter-electrode spacing (5-12 mm), width (1-3 mm), length (3-10 mm), shapes (bar, dot and circle), and the coupling gel's electrical conductivity (0.2-1.5 S/m) were simulated. The maximum temperature at 2 mm depth (T-2 mm ) and the temperature difference (Tdiff ) between the maximum skin surface temperature and T-2 mm were obtained to evaluate the effectiveness and safety.

RESULTS

The effect of geometric parameters on the effectiveness and safety was mixed. The maximum T-2 mm occurred with the 5 mm inter-electrode spacing, 3 mm width, 10 mm length, the circle-shaped electrode, and the 1.5 S/m coupling gel's electrical conductivity. The ratio of inter-electrode spacing to width at around four can achieve rapid temperature rise and skin surface temperature protection. The electrode shape influenced the area of temperature rise in the tissue's cross-section. The coupling gel's electrical conductivity should be close to that of the skin to avoid energy accumulation on the skin surface.

CONCLUSION

The electrode's geometric parameters affect the effectiveness and safety of the RF product. This study has provided the simulation procedure for the electrode design.

Structural design optimization and lipolytic effect prediction of vacuum suction cryolipolysis applicator: Simulation study

BACKGROUND AND OBJECTIVES

Cryolipolysis is a popular noninvasive lipolytic method that uses low temperature to induce apoptosis or necrosis of adipocytes to reduce local fat in the human body. Vacuum suction applicator is a commonly used cryolipolysis equipment, which suction human skin and fat into a chamber for cooling. The structure of vacuum suction applicator is usually irregular, its cooling characteristic is also complex, and unreasonable suction structure will cause human discomfort. Biological experiments and clinical studies are often used to study the structural design of applicators, whereas these methods are impossible to obtain the three-dimensional cooling characteristic of applicator comprehensively and require a lot of costs. This study aims to optimize the structure of applicator for lowering discomfort, evaluate the cooling characteristic and lipolytic effect of applicators, which could provide guidance for clinical application of applicators and reduce costs.

MATERIALS AND METHODS

Cryolipolysis applicators models with four vacuum suction angles were established, and COMSOL was used to compare the cooling performance parameters, cooling kinetics, and lipolytic effects of the applicators. Specific evaluation indicators also include: cooling capacity analysis, temperature field analysis, lipolytic percentage, lipolytic volume, lipolytic weight, lipolytic thickness, lipolytic waistline, and lipolysis temperature threshold analysis.

RESULTS

The applicator with a small suction angle has a greater cooling capacity to cool deeper level of fat. When the cooling temperature is -10°C, the temperature of skin layer is about -10°C at 60 minutes, the temperature of fat layer is -7.36 to 3.01°C at 10 mm, -3.67 to 5.91°C at 20 mm and 2.01-10.81°C at 30 mm. The percentage of lipolytic declined with the increase of suction angle, the final lipolytic percentage (35.81%) of the 90° applicator is the highest, the percentage (28.72%) of 150° applicator (28.72%) is the lowest. The lipolytic volume, weight, and average thickness of applicator constantly increased with the increase of the suction angle, the final lipolytic volume range of the four suction angle applicators is 171.88-310.18 cm³ , the lipolytic weight range is 160.11-288.93 g, and the lipolytic average thickness range is 1.21-1.36 cm. Lower lipolysis temperature threshold will reduce the lipolysis effect, but it may also lead to another lipolysis mechanism-cell necrosis.

CONCLUSION

Different suction angles significantly affect the cooling characteristics and lipolytic effects of cryolipolysis applicator. A reasonable suction angle is one of the critical factors to improve the efficiency and comfort of cryolipolysis.

Minimizing thermal damage using self-cooling jaws for radiofrequency intestinal tissue fusion

INTRODUCTION

Radiofrequency (RF)-induced tissue fusion shows great potential in sealing intestinal tissue without foreign materials. To improve the performance of RF-induced tissue fusion, a novel self-cooling jaw has been designed to minimize thermal damage during the fusion.

MATERIAL AND METHODS

The prototype of self-cooling jaws was developed and manufactured. A total number of 60 mucosa-to-mucosa fusions were conducted using ex-vivo porcine intestinal segments with the proposed design and conventional bipolar jaws. The effects of intestinal fusion were evaluated based on temperature curves, burst pressure, thermal damage, and histological appearances.

RESULTS

The self-cooling jaws showed significant decrease in temperature during the fusion process. An optimal burst pressure (5.7 ± 0.5 kPa) and thermal damage range (0.9 ± 0.1 mm) were observed when the applied RF power was 100 W. The thermal damage range of the prototype has almost decreased 36% in comparison with the conventional bipolar jaws (1.4 ± 0.1 mm). The histological observation revealed that a decrease of thermal damage was achieved through the application of self-cooling jaws.

CONCLUSIONS

The self-cooling jaws were proved to be effective for reducing the thermal damage during RF-induced tissue fusion, which could potentially promote the clinical application of tissue fusion techniques in the future.

A Multi-Site, Single-Blinded, Prospective Pilot Clinical Trial for Non-Invasive Fat Reduction of the Abdomen and Flanks Using a Monopolar 2 MHz Radiofrequency Device

BACKGROUND AND OBJECTIVES

Demand for non-invasive body sculpting procedures has been steadily increasing, spurring the development of new energy-based technologies. This study assessed the safety and efficacy of a new monopolar 2 MHz radiofrequency (RF) device for fat reduction of the flanks and abdomen.

STUDY DESIGN/MATERIALS AND METHODS

Nineteen subjects from two clinical sites were enrolled in this study and received a single 15-minute treatment with the 2 MHz RF device. Up to six applicators were placed on the abdomen and/or flanks during the treatment. Follow-up assessments were scheduled 12 weeks after treatment. Efficacy evaluations included live ratings and Global Aesthetic Improvement Scale (GAIS) ratings by blinded investigators, ultrasound measurements of fat thickness, and patient-reported outcomes before and after treatment.

RESULTS

Investigator assessments showed more than one-point change in the GAIS scale at the 12-week follow-up visit. Ultrasound measurements revealed a significant reduction in fat thickness in both the abdomen (average 24%) and the flanks (22%). The majority of the patients were satisfied with the treatment and mild self-resolving side effects were observed. No serious adverse events were reported.

CONCLUSIONS

Treatment of local adiposities with a new monopolar 2 MHz radiofrequency device leads to improvement of body contour with no downtime or side effects. Lasers Surg. Med. © 2020 Wiley Periodicals LLC.