Effect of Fibrous Septa in Radiofrequency Heating of Cutaneous and Subcutaneous Tissues: Computational Study

Simulation-guided development of advanced PID control algorithm for skin cooling in radiofrequency lipolysis

BACKGROUND

The clinical outcomes of bipolar radiofrequency (RF) lipolysis, a prevalent non-invasive fat reduction procedure, hinge on the delicate balance between effective lipolysis and patient safety, with skin overheating and subsequent tissue damage as primary concerns.

OBJECTIVE

This study aimed to investigate a novel bipolar radiofrequency lipolysis technique, safeguarding the skin through an innovative PID temperature control algorithm.

METHODS

Utilizing COMSOL Multiphysics simulation software, a two-dimensional fat and skin tissue model was established, simulating various PID temperature control schemes. The crux of the simulation involved a comparative analysis of different PID temperatures at 45 °C, 50 °C, and 55 °C and constant power strategies, assessing their implications on skin temperature. Concurrently, a custom bipolar radiofrequency lipolysis device was developed, with ex vivo experiments conducted using porcine tissue for empirical validation.

RESULTS

The findings indicated that with PID settings of Kp = 7, Ki = 2, and Kd = 0, and skin temperature control at 45 °C or 50 °C, the innovative PID-based epidermal temperature control strategy successfully maintained the epidermal temperature within a safe range. This maintenance was achieved without compromising the effectiveness of RF lipolysis, significantly reducing the risk of thermal damage to the skin layers.

CONCLUSION

Our research confirms the substantial practical utility of this advanced PID-based bipolar RF lipolysis technique in clinical aesthetic procedures, enhancing patient safety during adipose tissue ablation therapies.

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.

A Three-dimensional Simulation Based on Radiofrequency Electrothermal Coupling fields for Skin Rejuvenation. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2023;2023:1-4. [PMID: 38083140 DOI: 10.1109/embc40787.2023.10340026] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Radiofrequency (RF) current is used as an effective non-ablative method for skin rejuvenation. However, mixed results have been reported using different home-use RF devices. In order to evaluate the safety and effectiveness of home-use RF devices, this study has provided a three-dimensional (3D) simulation procedure based on the electrothermal coupling model for home-use RF devices. Firstly, the tissue geometric model with the setting electrode shapes was established and then imported into the simulation software. Secondly, electrical and thermal boundary conditions with excitation voltages were loaded to the corresponding components. In addition, the items of 3D temperatures at all locations and key temperatures of the tissue were assessed. The results have shown the temperature distributions of four commercial RF products, respectively. This 3D RF electrothermal coupling simulation can be conducted quickly and effectively to obtain the temperature and electric distribution of the home-use RF devices at different using periods, which is also useful for the design of home-use RF devices.Clinical Relevance- This study provides a simple and effective simulation procedure for device developers to evaluate the home-use RF devices when designing products. This simulation is also helpful for customer decision-making and performance evaluation considering different devices.

Transport and distribution of biotherapeutics in different tissue layers after subcutaneous injection

The subcutaneous injection is the main route of administration for monoclonal antibodies (mAbs) and several other biotherapeutics due to the patient comfort and cost-effectiveness. However, their transport and distribution after subcutaneous injection is poorly understood. Here, we exploit a three-dimensional poroelastic model to find the biomechanical response of the tissue, including interstitial pressure and tissue deformation during the injection. We quantify the drug concentration inside the tissue. We start with a single-layer model of the tissue. We show that during injection, the difference between the permeability of the solvent and solute will result in a higher drug concentration proportional to the inverse permeability ratio. Then we study the role of tissue layered properties with primary layers, including epidermis, dermis, subcutaneous (SQ), and muscle layers, on tissue biomechanical response to injection and drug transport. We show that the drug will distribute mainly in the SQ layer due to its lower elastic moduli. Finally, we study the effect of secondary tissue elements like the deep fascia layer and the network of septa fibers inside the SQ tissue. We use the Voronoi algorithm to create random geometry of the septa network. We show how drugs accumulate around these tissue components as observed in experimental SQ injection. Next, we study the effect of injection rate on drug concentration. We show how higher injection rates will slightly increase the drug concentration around septa fibers. Finally we demonstrate how the concentration dependent viscosity will increase the concentration of biotherapeutics in the direction of septa fibers. .

Multicenter Pivotal Study Demonstrates Safety and Efficacy of a New Cellulite Procedure: 3-Month Results

BACKGROUND

Cellulite is an aesthetic condition affecting the appearance of skin in certain body regions and is associated with body dissatisfaction, psychosocial stress, and decreased quality of life. Previous studies established the safety and feasibility of a novel, minimally invasive device to identify and release septa responsible for cellulite depressions: targeted verifiable subcision (TVS).

OBJECTIVES

The objective of this single-arm, open-label, multicenter study was to evaluate the safety and efficacy of TVS for reducing the appearance of moderate to severe cellulite in adult women.

METHODS

Adult women aged 21 to 55 years and a BMI < 30 kg/m2 with moderate or severe cellulite on the buttocks and/or thighs were eligible to enroll at 9 sites. Endpoint data included results from 4 of the postprocedural follow-up visits at 24 hours, 7 days, 30 days, and 90 days. The primary endpoints were a mean ≥1 point reduction in the Cellulite Severity Scale at 90 days and no related serious adverse events at 30 days.

RESULTS

Seventy-four female participants with a mean BMI of 24.8 ± 2.7 and age of 41.4 ± 7.4 years received this single procedure. The mean improvement in Cellulite Severity Scale (N = 68) was 1.5 ± 0.9 (P < 0.0001). There were no device-related serious adverse events at 30 days.

CONCLUSIONS

TVS for selectively identifying and verifiably releasing septa responsible for cellulite depressions is an effective and safe means to improve the appearance of moderate to severe cellulite in adult women.

LEVEL OF EVIDENCE: 2

Depth of thermal dispersion of monopolar radiofrequency heating in the vaginal wall

The use of energy-based devices to treat genitourinary syndrome of menopause, termed vaginal thermotherapy (VTT), has gained significant interest in recent years. Among the primary safety concerns of this relatively new procedure is the possibility of unintentionally heating tissues adjacent to the vaginal wall, i.e., heating too deeply. Herein we use numerical simulations to evaluate monopolar radiofrequency-based (RF) VTT specifically focusing on the resultant depth of heating through a range of input parameters. Varying RF power, exposure time, and the simulated rate of blood perfusion, we map the parameter space identifying which combinations of input parameters are likely to heat past the depth of the vaginal wall and affect adjacent tissue. We found that the device parameters commonly used in the literature are likely to heat past the vaginal wall and merit further investigation. In addition, we found that the parameter typically used to describe VTT devices, total energy delivered, does not reliably indicate the resultant depth of heat dispersion.

A Computational and Experimental Study to Compare the Effectiveness of Bipolar Mode With Phase-Shift Angle Mode in Radiofrequency Fat Dissolution on Subcutaneous Tissue

BACKGROUND AND OBJECTIVES

Radiofrequency (RF) energy exposure refers to a popular non-invasive method employed to generate heat in cutaneous and subcutaneous tissues. RF thermal stimulation of adipose tissue has been considered to cause adipocyte metabolism and enzymatic degradation of triglycerides into free fatty acids and glycerol. Bipolar mode (BM) has achieved extensive applications in clinical studies on RF fat dissolution, whereas BM has a less penetration depth than monopolar, result in a higher RF voltage that may be required to increase power to the deeper fat layer of the subcutaneous tissue, and improper power control may easily cause the skin layer to be thermally damaged. To tackle down the mentioned defect, a novel phase-shift angle mode (PM) was proposed in this study based on double-channel bipolar RF. By employing the finite element method (FEM) and performing the ex vivo experiment, the effectiveness of BM was compared with that of PM in RF fat dissolution on subcutaneous tissue. In addition, this study attempted to develop reasonable phase-shift angles capable of achieving fat dissolution effects, while the RF energy of which would not cause the skin layer to be thermally damaged.

STUDY DESIGN/MATERIALS AND METHODS

Two electrode spacings (1 and 2 cm) were applied in BM (BM-1 cm and BM-2 cm, respectively), and six phase-shift angles (i.e., 30°, 60°, 90°, 120°, 150°, and 180°) were set in PM (i.e., PM-30°, PM-60°, PM-90°, PM-120°, PM-150°, and PM-180°). In addition, COMSOL was adopted to conduct a finite element analysis for achieving thermoelectric coupling. Ex vivo experiments were performed with a self-developed double-channel bipolar RF device, through which up to two adjustable phase-shift angle sinusoidal voltages could be generated. Such a device was isolated with a transformer and then connected to four electrodes with a 5 mm diameter contacting the ex vivo porcine abdominal tissue.

RESULTS

Under the RF voltage amplitude of 30 V, and after 1800 seconds of RF heating, no thermally damaged area was formed in the tissue in BM-1 cm and BM-2 cm; in PM-30°, PM-60°, and PM-90°, thermally damaged areas were formed in the fat layer, while the skin layer was not located in the thermally damaged area. Moreover, the temperature in the thermally damaged area attributed to the mentioned three conditions may satisfy the requirement of fat dissolution temperature.

CONCLUSIONS

Under the identical RF voltage and heating time, PM is easier to cause the fat layer of the subcutaneous tissue to be thermally damaged as compared with BM. Accordingly, PM may be enabled to achieve the fat dissolution effect under a relatively low RF voltage as opposed to BM, thus avoiding the possibility of thermal damage of the skin layer attributed to the use of higher RF voltage. In PM, different phase-shift angle significantly affects the electrical and thermal properties of RF energy applied on subcutaneous tissue; the phase-shift angle of RF voltage is likely to be regulated for fat dissolution effect, while the RF energy of which will not cause the skin layer to be thermally damaged.© 2021 Wiley Periodicals LLC.

Deletion of adipocytes induced by a novel device simultaneously delivering synchronized radiofrequency and hifem: Human histological study

BACKGROUND

Radiofrequency (RF) is commonly recognized treatment option for fat reduction, utilizing heat-induced adipocyte deletion. HIFEM treatment has been proven to be an effective tool for body shaping.

OBJECTIVES

To document the structural changes in human subcutaneous tissue induced by the combination of RF treatment with the HIFEM procedure.

METHODS

Four subjects (51.50 ± 6.35 years, 22.59 ± 3.21 kg/m² ) received three 30-minute abdominal treatments consisting of RF therapy and HIFEM. One subject (57 years, 23.60 kg/m² ) served as a control. Punch biopsies were collected at baseline, 1-week, and 1-month post-treatment. Samples were sliced and stained with H&E. Waist circumference, digital photographs, satisfaction, and therapy comfort were assessed. Subjects were monitored for any adverse event, and fat temperatures were measured.

RESULTS

Baseline samples showed a healthy appearance of adipocytes, composed of round-shaped unilocular cells of uniform size. At follow-up, treated adipocytes demonstrated nuclear and shape changes with consequent fat reduction. Adipocytes were found to be flattened/shrunken and of smaller size (-33.5% at 1 week; -31.7% at 1-month) along with occasional ruptures of the cytoplasmic membrane. In contrast to baseline, pyknotic nuclei with condensed nuclear chromatin were seen at 1-week and 1-month post-treatment. The control samples showed no treatment-related changes. Waist circumference decreased by an average of 2.20 cm in the treated patients. No adverse events were observed. The fat temperature reached 42-45°C, during treatment; the therapy was comfortable with high patient satisfaction.

CONCLUSIONS

Results suggest the efficacy and safety of the therapy combining RF and HIFEM. The adipocyte deletion and shrinkage resulted in overall reduction of fat tissue.

Thermal field and tissue damage analysis of moving laser in cancer thermal therapy

In this paper, a closed-form analytical solution of hyperbolic Pennes bioheat equation is obtained for spatial evolution of temperature distributions during moving laser thermotherapy of the skin and kidney tissues. The three-dimensional cubic homogeneous perfused biological tissue is adopted as a media and the Gaussian distributed function in surface and exponentially distributed in depth is used for modeling of laser moving heat source. The solution procedure is Eigen value method which leads to a closed form solution. The effect of moving velocity, perfusion rate, laser intensity, absorption and scattering coefficients, and thermal relaxation time on temperature profiles and tissue thermal damage are investigated. Results are illustrated that the moving velocity and the perfusion rate of the tissues are the main important parameters in produced temperatures under moving heat source. The higher perfusion rate of kidney compared with skin may lead to lower induced temperature amplitude in moving path of laser due to the convective role of the perfusion term. Furthermore, the analytical solution can be a powerful tool for analysis and optimization of practical treatment in the clinical setting and laser procedure therapeutic applications and can be used for verification of other numerical heating models.

Relation between denaturation time measured by optical coherence reflectometry and thermal lesion depth during radiofrequency cardiac ablation: Feasibility numerical study

BACKGROUND/OBJECTIVE

Radiofrequency (RF) catheter ablation is a minimally invasive medical procedure used to thermally destroy the focus of cardiac arrhythmias. Novel optical techniques are now being integrated into RF catheters in order to detect the changes in tissue properties. Loss of birefringence due to fiber denaturation at around 70°C is related to changes in accumulated phase retardation and can be measured by polarization-sensitive optical coherence reflectometry (PS-OCR). Since irreversible thermal lesions are produced when the tissue reaches 50°C, our goal was to seek the mathematical relationship between both isotherms.

MATERIALS AND METHODS

A two-dimensional model based on a coupled electric-thermal problem was built and solved using the finite element method. The model consisted of cardiac tissue, blood, and a non-irrigated electrode with a sensor embedded in its tip to maintain a specific target electrode temperature. Computer simulations were conducted by varying the tissue characteristics. Lesion depth was estimated by the 50°C isotherm, while the denaturation time (TD) was taken as the time at which the 70°C isotherm reached a depth of 0.75 mm (which corresponds to the optical depth reached by PS-OCR technology).

RESULTS

A strong correlation (R²  > 0.83) was found between TD and lesion depth and an even stronger correlation (R² > 0.96) was found between TD and the time required to achieve a specific lesion depth. For instance, the ablation time required to ensure a minimum lesion depth of 3 mm was 1.33 × TD + 3.93 × seconds.

CONCLUSIONS

The computer results confirmed the strong relationship between denaturation time and lesion depth and suggest that measuring denaturation time by PS-OCR could provide information on the ablation time required to reach a specific lesion depth. Lasers Surg. Med. 50:222-229, 2018. © 2017 Wiley Periodicals, Inc.

Effects of Multipolar Radiofrequency and Pulsed Electromagnetic Field Treatment for Face and Neck Rejuvenation

Skin aging is a gradual process that leads to wrinkle formation, laxity, and overall changes in skin appearance. In recent years, the demands to noninvasive treatments for facial rejuvenation increased, along with a variety of technologies and devices, such as radiofrequency. The present study aimed to evaluate the clinical effects of a multipolar radiofrequency and pulsed electromagnetic field treatment for face and neck rejuvenation. Eleven patients with mild to moderate grades of photoaging underwent eight radiofrequency and pulsed electromagnetic field treatment sessions, once a week. Clinical photographs were taken before and a week after the end of the treatment, and improvement of facial skin parameters was evaluated by two different investigators. Significant improvement in skin laxity was observed in all eleven patients (100%). Improvement in facial contour was noted in 73% and 100% of patients when analyzed by investigators A and B, respectively. The score for overall improvement in skin condition was 3 ± 0.78 for investigator A and 3.6 ± 0.67 for investigator B. All patients were satisfied with the procedure and noted significant improvement in the skin. The combined multipolar radiofrequency and pulsed electromagnetic field device is effective and safe for treatment of aged skin in Brazilian patients.

Microstructural inhomogeneity of electrical conductivity in subcutaneous fat tissue

Microscopic peculiarities stemming from a temperature increase in subcutaneous adipose tissue (sWAT) after applying a radio-frequency (RF) current, must be strongly dependent on the type of sWAT. This effect is connected with different electrical conductivities of pathways inside (triglycerides in adipocytes) and outside (extra-cellular matrix) the cells and to the different weighting of these pathways in hypertrophic and hyperplastic types of sWAT. The application of the RF current to hypertrophic sWAT, which normally has a strongly developed extracellular matrix with high concentrations of hyaluronan and collagen in a peri-cellular space of adipocytes, can produce, micro-structurally, a highly inhomogeneous temperature distribution, characterized by strong temperature gradients between the peri-cellular sheath of the extra-cellular matrix around the hypertrophic adipocytes and their volumes. In addition to normal temperature effects, which are generally considered in body contouring, these temperature gradients can produce thermo-mechanical stresses on the cells’ surfaces. Whereas these stresses are relatively small under normal conditions and cannot cause any direct fracturing or damage of the cell structure, these stresses can, under some supportive conditions, be theoretically increased by several orders of magnitude, causing the thermo-mechanical cell damage. This effect cannot be realized in sWAT of normal or hyperplastic types where the peri-cellular structures are under-developed. It is concluded that the results of RF application in body contouring procedures must be strongly dependent on the morphological structure of sWAT.