Coupled thermo-electro-mechanical models for thermal ablation of biological tissues and heat relaxation time effects

Non-Fourier Bioheat Transfer Analysis in Brain Tissue During Interstitial Laser Ablation: Analysis of Multiple Influential Factors

This work presents the dual-phase lag-based non-Fourier bioheat transfer model of brain tissue subjected to interstitial laser ablation. The finite element method has been utilized to predict the brain tissue's temperature distributions and ablation volumes. A sensitivity analysis has been conducted to quantify the effect of variations in the input laser power, treatment time, laser fiber diameter, laser wavelength, and non-Fourier phase lags. Notably, in this work, the temperature-dependent thermal properties of brain tissue have been considered. The developed model has been validated by comparing the temperature obtained from the numerical and ex vivo brain tissue during interstitial laser ablation. The ex vivo brain model has been further extended to in vivo settings by incorporating the blood perfusion effects. The results of the systematic analysis highlight the importance of considering temperature-dependent thermal properties of the brain tissue, non-Fourier behavior, and microvascular perfusion effects in the computational models for accurate predictions of the treatment outcomes during interstitial laser ablation, thereby minimizing the damage to surrounding healthy tissue. The developed model and parametric analysis reported in this study would assist in a more accurate and precise prediction of the temperature distribution, thus allowing to optimize the thermal dosage during laser therapy in the brain.

Heat transfer analysis for tissue with surface heat flux based on the non-linearized form of the three-phase-lag model

The three-phase-lag model of heat conduction has been proposed for considering thermoelastic effect in medium. The bioheat transfer equations based on Taylor's series approximation of the three-phase-lag model were derived in conjunction with a modified energy conservation equation. For exploring the effect of non-linear expansion in the phase lag times, the Taylor's series of second-order expansion was applied. The resulting equation involves mixed derivative terms and higher-order derivatives of temperature with respect to time. The hybrid application of the Laplace transform method and a modified discretization technique was extended to solve the equations and explore the effect of thermoelasticity on the thermal behavior in living tissue with surface heat flux. The influence of thermoelastic parameters and phase lags on heat transfer in tissue has been investigated. The present results illustrate the thermal response oscillation is excited in medium for the thermoelastic effect, the phase lag times significantly affect the amplitude and frequency of the oscillation, and the expansion order of TPL model evidently affects the predicted temperature.

Three-Phase-Lag Bio-Heat Transfer Model of Cardiac Ablation

Significant research efforts have been devoted in the past decades to accurately modelling the complex heat transfer phenomena within biological tissues. These modeling efforts and analysis have assisted in a better understanding of the intricacies of associated biological phenomena and factors that affect the treatment outcomes of hyperthermic therapeutic procedures. In this contribution, we report a three-dimensional non-Fourier bio-heat transfer model of cardiac ablation that accounts for the three-phase-lags (TPL) in the heat propagation, viz., lags due to heat flux, temperature gradient, and thermal displacement gradient. Finite element-based COMSOL Multiphysics software has been utilized to predict the temperature distributions and ablation volumes. A comparative analysis has been conducted to report the variation in the treatment outcomes of cardiac ablation considering different bio-heat transfer models. The effect of variations in the magnitude of different phase lags has been systematically investigated. The fidelity and integrity of the developed model have been evaluated by comparing the results of the developed model with the analytical results of the recent studies available in the literature. This study demonstrates the importance of considering non-Fourier lags within biological tissue for predicting more accurately the characteristics important for the efficient application of thermal therapies.

Multiscale and Multiphysics Modeling of Anisotropic Cardiac RFCA: Experimental-Based Model Calibration via Multi-Point Temperature Measurements

Radiofrequency catheter ablation (RFCA) is the mainstream treatment for drug-refractory cardiac fibrillation. Multiple studies demonstrated that incorrect dosage of radiofrequency energy to the myocardium could lead to uncontrolled tissue damage or treatment failure, with the consequent need for unplanned reoperations. Monitoring tissue temperature during thermal therapy and predicting the extent of lesions may improve treatment efficacy. Cardiac computational modeling represents a viable tool for identifying optimal RFCA settings, though predictability issues still limit a widespread usage of such a technology in clinical scenarios. We aim to fill this gap by assessing the influence of the intrinsic myocardial microstructure on the thermo-electric behavior at the tissue level. By performing multi-point temperature measurements on ex-vivo swine cardiac tissue samples, the experimental characterization of myocardial thermal anisotropy allowed us to assemble a fine-tuned thermo-electric material model of the cardiac tissue. We implemented a multiphysics and multiscale computational framework, encompassing thermo-electric anisotropic conduction, phase-lagging for heat transfer, and a three-state dynamical system for cellular death and lesion estimation. Our analysis resulted in a remarkable agreement between ex-vivo measurements and numerical results. Accordingly, we identified myocardium anisotropy as the driving effect on the outcomes of hyperthermic treatments. Furthermore, we characterized the complex nonlinear couplings regulating tissue behavior during RFCA, discussing model calibration, limitations, and perspectives.

Fluid–Structure Interaction and Non-Fourier Effects in Coupled Electro-Thermo-Mechanical Models for Cardiac Ablation

In this study, a fully coupled electro-thermo-mechanical model of radiofrequency (RF)-assisted cardiac ablation has been developed, incorporating fluid–structure interaction, thermal relaxation time effects and porous media approach. A non-Fourier based bio-heat transfer model has been used for predicting the temperature distribution and ablation zone during the cardiac ablation. The blood has been modeled as a Newtonian fluid and the velocity fields are obtained utilizing the Navier–Stokes equations. The thermal stresses induced due to the heating of the cardiac tissue have also been accounted. Parametric studies have been conducted to investigate the effect of cardiac tissue porosity, thermal relaxation time effects, electrode insertion depths and orientations on the treatment outcomes of the cardiac ablation. The results are presented in terms of predicted temperature distributions and ablation volumes for different cases of interest utilizing a finite element based COMSOL Multiphysics software. It has been found that electrode insertion depth and orientation has a significant effect on the treatment outcomes of cardiac ablation. Further, porosity of cardiac tissue also plays an important role in the prediction of temperature distribution and ablation volume during RF-assisted cardiac ablation. Moreover, thermal relaxation times only affect the treatment outcomes for shorter treatment times of less than 30 s.

Auxeticity in biosystems: an exemplification of its effects on the mechanobiology of heterogeneous living cells

Auxeticity (negative Poisson's ratio) is the unique mechanical property found in an extensive variety of materials, such as metals, graphene, composites, polymers, foams, fibers, ceramics, zeolites, silicates and biological tissues. The enhanced mechanical features of the auxetic materials have motivated scientists to design, engineer and manufacture man-made auxetic materials to fully leverage their capabilities in different fields of research applications, including aeronautics, medical, protective equipments, smart sensors, filter cleaning, and so on. Atomic force microscopy (AFM) indentation is one of the most widely used methods for characterizing the mechanical properties and response of the living cells. In this contribution, we highlight main consequences of auxeticity for biosystems and provide a representative example to quantify the effect of nucleus auxeticity on the force response of the embryonic stem cells. A parametric study has been conducted on a heterogeneous stem cell to evaluate the effect of nucleus diameter, nucleus elasticity, indenter's shape and location on the force-indentation curve. The developed model has also been validated with the recently reported experimental studies available in the literature. Our results suggest that the nucleus auxeticity plays a profound role in cell mechanics especially for large size nucleus. We also report the mechanical stresses induced within the hyperelastic cell model under different loading conditions that would be quite useful in decoding the interrelations between mechanical stimuli and cellular behavior of auxetic biosystems. Finally, current and potential areas of applications of our findings for regenerative therapies, tissue engineering, 3 D/4D bioprinting, and the development of meta-biomaterials are discussed.

Short pulsed microwave ablation: computer modeling and ex vivo experiments

PURPOSE

To study the differences between continuous and short-pulse mode microwave ablation (MWA).

METHODS

We built a computational model for MWA including a 200 mm long and 14 G antenna from Amica-Gen and solved an electromagnetic-thermal coupled problem using COMSOL Multiphysics. We compared the coagulation zone (CZ) sizes created with pulsed and continuous modes under ex vivo and in vivo conditions. The model was used to compare long vs. short pulses, and 1000 W high-powered short pulses. Ex vivo experiments were conducted to validate the model.

RESULTS

The computational models predicted the axial diameter of the CZ with an error of 2-3% and overestimated the transverse diameter by 9-11%. For short pulses, the ex vivo computer modeling results showed a trend toward larger CZ when duty cycles decreases. In general, short pulsed mode yielded higher CZ diameters and volumes than continuous mode, but the differences were not significant (<5%), as in terms of CZ sphericity. The same trends were observed in the simulations mimicking in vivo conditions. Both CZ diameter and sphericity were similar with short and long pulses. Short 1000 W pulses produced smaller sphericity and similar CZ sizes under in vivo and ex vivo conditions.

CONCLUSIONS

The characteristics of the CZ created by continuous and pulsed MWA show no significant differences from ex vivo experiments and computer simulations. The proposed idea of enlarging coagulation zones and improving their sphericity in pulsed mode was not evident in this study.

Sublethal hyperthermia enhances anticancer activity of doxorubicin in chronically hypoxic HepG2 cells through ROS-dependent mechanism

Thermal ablation in combination with transarterial chemoembolization (TACE) has been reported to exert a more powerful antitumor effect than thermal ablation alone in hepatocellular carcinoma patients. However, the underlying mechanisms remain unclear. The purpose of the present study was to evaluate whether sublethal hyperthermia encountered in the periablation zone during thermal ablation enhances the anticancer activity of doxorubicin in chronically hypoxic (encountered in the tumor area after TACE) liver cancer cells and to explore the underlying mechanisms. In the present study, HepG2 cells precultured under chronic hypoxic conditions (1% oxygen) were treated in a 42°C water bath for 15 or 30 min, followed by incubation with doxorubicin. Assays were then performed to determine intracellular uptake of doxorubicin, cell viability, apoptosis, cell cycle, mitochondrial membrane potential (MMP), reactive oxygen species (ROS), and total antioxidant capacity. The results confirmed that sublethal hyperthermia enhanced the intracellular uptake of doxorubicin into hypoxic HepG2 cells. Hyperthermia combined with doxorubicin led to a greater inhibition of cell viability and increased apoptosis in hypoxic HepG2 cells as compared with hyperthermia or doxorubicin alone. In addition, the combination induced apoptosis by increasing ROS and causing disruption of MMP. Pretreatment with the ROS scavenger N-acetyl cysteine significantly inhibited the apoptotic response, suggesting that cell death is ROS-dependent. These findings suggested that sublethal hyperthermia enhances the anticancer activity of doxorubicin in hypoxic HepG2 cells via a ROS-dependent mechanism.

Computational Modeling of Cardiac Ablation Incorporating Electrothermomechanical Interactions

The application of radio frequency ablation (RFA) has been widely explored in treating various types of cardiac arrhythmias. Computational modeling provides a safe and viable alternative to ex vivo and in vivo experimental studies for quantifying the effects of different variables efficiently and reliably, apart from providing a priori estimates of the ablation volume attained during cardiac ablation procedures. In this contribution, we report a fully coupled electrothermomechanical model for a more accurate prediction of the treatment outcomes during the radio frequency cardiac ablation. A numerical model comprising of cardiac tissue and the cardiac chamber has been developed in which an electrode has been inserted perpendicular to the cardiac tissue to simulate actual clinical procedures. Temperature-dependent heat capacity, electrical and thermal conductivities, and blood perfusion rate have been considered to model more realistic scenarios. The effects of blood flow and contact force of the electrode tip on the treatment outcomes of a fully coupled model of RFA have been systematically investigated. The numerical study demonstrates that the predicted ablation volume of RFA is significantly dependent on the blood flow rate in the cardiac chamber and also on the tissue deformation induced due to electrode insertion depth of 1.5 mm or higher.

Domain Heterogeneity in Radiofrequency Therapies for Pain Relief: A Computational Study with Coupled Models

The objective of the current research work is to study the differences between the predicted ablation volume in homogeneous and heterogeneous models of typical radiofrequency (RF) procedures for pain relief. A three-dimensional computational domain comprising of the realistic anatomy of the target tissue was considered in the present study. A comparative analysis was conducted for three different scenarios: (a) a completely homogeneous domain comprising of only muscle tissue, (b) a heterogeneous domain comprising of nerve and muscle tissues, and (c) a heterogeneous domain comprising of bone, nerve and muscle tissues. Finite-element-based simulations were performed to compute the temperature and electrical field distribution during conventional RF procedures for treating pain, and exemplified here for the continuous case. The predicted results reveal that the consideration of heterogeneity within the computational domain results in distorted electric field distribution and leads to a significant reduction in the attained ablation volume during the continuous RF application for pain relief. The findings of this study could provide first-hand quantitative information to clinical practitioners about the impact of such heterogeneities on the efficacy of RF procedures, thereby assisting them in developing standardized optimal protocols for different cases of interest.

Thermal ablation of biological tissues in disease treatment: A review of computational models and future directions

Percutaneous thermal ablation has proven to be an effective modality for treating both benign and malignant tumours in various tissues. Among these modalities, radiofrequency ablation (RFA) is the most promising and widely adopted approach that has been extensively studied in the past decades. Microwave ablation (MWA) is a newly emerging modality that is gaining rapid momentum due to its capability of inducing rapid heating and attaining larger ablation volumes, and its lesser susceptibility to the heat sink effects as compared to RFA. Although the goal of both these therapies is to attain cell death in the target tissue by virtue of heating above 50°C, their underlying mechanism of action and principles greatly differs. Computational modelling is a powerful tool for studying the effect of electromagnetic interactions within the biological tissues and predicting the treatment outcomes during thermal ablative therapies. Such a priori estimation can assist the clinical practitioners during treatment planning with the goal of attaining successful tumour destruction and preservation of the surrounding healthy tissue and critical structures. This review provides current state-of-the-art developments and associated challenges in the computational modelling of thermal ablative techniques, viz., RFA and MWA, as well as touch upon several promising avenues in the modelling of laser ablation, nanoparticles assisted magnetic hyperthermia and non-invasive RFA. The application of RFA in pain relief has been extensively reviewed from modelling point of view. Additionally, future directions have also been provided to improve these models for their successful translation and integration into the hospital work flow.