MRI-based finite element simulation on radiofrequency ablation of thyroid cancer

Model-Optimizing Radiofrequency Parameters of 3D Finite Element Analysis for Ablation of Benign Thyroid Nodules

Radiofrequency (RF) ablation represents an efficient strategy to reduce the volume of thyroid nodules. In this study, a finite element model was developed with the aim of optimizing RF parameters, e.g., input power and treatment duration, in order to achieve the target volume reduction rate (VRR) for a thyroid nodule. RF ablation is modelled as a coupled electro-thermal problem wherein the electric field is applied to induce tissue heating. The electric problem is solved with the Laplace equation, the temperature distribution is estimated with the Pennes bioheat equation, and the thermal damage is evaluated using the Arrhenius equation. The optimization model is applied to RF electrode with different active tip lengths in the interval from 5 mm to 40 mm at the 5 mm step. For each case, we also explored the influence of tumour blood perfusion rate on RF ablation outcomes. The model highlights that longer active tips are more efficient as they require lesser power and shorter treatment time to reach the target VRR. Moreover, this condition is characterized by a reduced transversal ablation zone. In addition, a higher blood perfusion increases the heat dispersion, requiring a different combination of RF power and time treatment to achieve the target VRR. The model may contribute to an improvement in patient-specific RF ablation treatment.

Numerical analysis of non-Fourier thermal response of lung tissue based on experimental data with application in laser therapy

BACKGROUND AND OBJECTIVE

The thermal therapy is a minimally invasive technique used as an alternative approach to conventional cancer treatments. There is an increasing concern about the accuracy of the thermal simulation during the process of tumor ablation. This study is aimed at investigating the effect of finite speed of heat propagation in the biological lung tissue, experimentally and numerically.

METHODS

In the experimental study, a boundary heat flux is applied to the lung tissue specimens and the temperature variation is measured during a transient heat transfer procedure. In the numerical study, a code is developed based on the finite volume method to solve the classical bio-heat transfer, the Cattaneo and Vernotte, and the Dual-phase-lag (DPL) equations. The thermal response of tissue during the experiments is compared with the predictions of the three heat transfer models.

RESULTS

It is found that the trend of temperature variation by the DPL model resembles the experimental results. The experimental observation in parallel with the numerical results reveals that the accumulated thermal energy diffuses to the surrounding tissue with a slower rate in comparison with the conventional bio-heat transfer model. The DPL model is implemented to study the temperature elevation in the laser irradiation to lung tissue in the presence of gold nanoparticles (GNPs). It is concluded that the extent of the necrotic tumoral region and the area of the damaged healthy tissue are reduced, when the non-Fourier heat transfer is taken into account.

CONCLUSIONS

Results show that considering the phase lags is crucial in planning for an effective thermal treatment, in which the cancerous tissue is ablated and the surrounding tissues are preserved from irreversible thermal damage.

EView: An electric field visualization web platform for electroporation-based therapies

BACKGROUND AND OBJECTIVES

Electroporation is the phenomenon by which cell membrane permeability to ions and macromolecules is increased when the cell is briefly exposed to high electric fields. In electroporation-based treatments, such exposure is typically performed by delivering high voltage pulses across needle electrodes in tissue. For a given tissue and pulsing protocol, an electric field magnitude threshold exists that must be overreached for treatment efficacy. However, it is hard to preoperatively infer the treatment volume because the electric field distribution intricately depends on the electrodes' positioning and length, the applied voltage, and the electric conductivity of the treated tissues. For illustrating such dependencies, we have created EView (https://eview.upf.edu), a web platform that estimates the electric field distribution for arbitrary needle electrode locations and orientations and overlays it on 3D medical images.

METHODS

A client-server approach has been implemented to let the user set the electrode configuration easily on the web browser, whereas the simulation is computed on a dedicated server. By means of the finite element method, the electric field is solved in a 3D volume. For the sake of simplicity, only a homogeneous tissue is modeled, assuming the same properties for healthy and pathologic tissues. The non-linear dependence of tissue conductivity on the electric field due to the electroporation effect is modeled. The implemented model has been validated against a state of the art finite element solver, and the server has undergone a heavy load test to ensure reliability and to report execution times.

RESULTS

The electric field is rapidly computed for any electrode and tissue configuration, and alternative setups can be easily compared. The platform provides the same results as the state of the art finite element solver (Dice = 98.3 ± 0.4%). During the high load test, the server remained responsive. Simulations are computed in less than 2 min for simple cases consisting of two electrodes and take up to 40 min for complex scenarios consisting of 6 electrodes.

CONCLUSIONS

With this free platform we provide expert and non-expert electroporation users a way to rapidly model the electric field distribution for arbitrary electrode configurations.

Microstructure-based non-Fourier heat transfer modeling of HIFU treatment for thyroid cancer

BACKGROUND AND OBJECTIVES

High intensity focused ultrasound is an emerging non-invasive technique for the thermal ablation of cancer. Modeling of high intensity focused ultrasound as a method to induce hyperthermia, by considering non-equilibrium convective heat transfer has been under-represented in the previous studies. Therefore, in the present study, we aimed to study the effect of blood vessels during high intensity focused ultrasound ablation of thyroid cancer. In addition, high intensity focused ultrasound modeling was greatly improved by considering non-Fourier heat transfer.

METHODS

The modified dual-phase-lag model was used for the modeling of heat transfer in thyroid cancer during the ultrasound irradiation. The model parameters were linked with the tissue's microstructure parameters. Meanwhile, an interfacial convective heat transfer was considered between the blood vessels and the extravascular matrix. The extent of the vascular region was determined using the field emission scanning electron microscopy images. The non-linear Westervelt equation was solved for the sound wave to determine the heat source for the induced hyperthermia treatment.

RESULTS

Referring to the acoustic results, sharp-wave ripples were observed due to the inclusion of notable amplitudes of excited harmonics. The thermal results showed a maximum temperature rise of 25.08°C and 51.47°C at the powers of 5 W and 10 W using the modified dual-phase-lag model, while the Pennes model predicted a temperature rise of 28.77°C and 55.5°C at the same powers. It was also concluded that a constant blood temperature, overestimates the dissipated energy and the temperature reduction during the cooling period, as a 15% deviation in the tumor temperature was observed from the non-equilibrium state at 10.65 s exposure and 10 W power. Eventually, the calculation of the ablated volumes indicated that the volumes were up to 4.5 times larger by the Pennes model compared to the modified dual-phase-lag model.

CONCLUSIONS

It can be concluded from the results that there should be a serious concern on the high intensity focused ultrasound modeling based on the parameters of blood vessels. Based on the thermal maps, the cancerous tissue should be exposed to a higher energy level of ultrasound waves in order to cause the desired damage against the estimated energy level predicted by the Pennes model.

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.

Analysis of thyroid thermographic images for detection of thyroid tumor: An experimental-numerical study

Thermography is a developing and noninvasive medical imaging technique that can be used for diagnosis of body disorders based on temperature deviation from normal body temperature. This research investigates the feasibility of thermography method in conjunction with artificial neural networks (ANNs) for detection of thyroid tumors. For this purpose, first, a 3-D model of the healthy human neck is constructed based on patient-specific computed tomography (CT) images. This model is used for analyzing bio-heat transfer in the human neck. The healthy thyroid gland is considered as a heat source and generates heat according to its temporal temperature. Finite element results verify the thermography potential for detection of thyroid gland location and estimation of its butterfly shape on the neck thermogram. The numerical analysis is carried out on 35 models with varying thermo-physical parameters of the healthy thyroid gland, including heat generation and blood perfusion. The acquired thermograms are used to develop an ANN for correlating the thermo-physical parameters of the gland and temperature profile on the neck surface. In the next stage, dynamic thermal images are captured from 10 healthy and three cancerous human cases. The experimental thermal images are analyzed by the developed ANN and the corresponding thermo-physical parameters are obtained. Results show that the estimated heat generation values for the healthy cases are about 3000 Wm3 while it increases to more than 12 000 Wm3 for the cases with tumors. This significant variation confirms the potential of dynamic thermography in diagnosis of thyroid tumors.

RF ablation thermal simulation model: Parameter sensitivity analysis

OBJECTIVE:

The aim of the research is to obtain the relative influences of some critical electro-thermal parameters on the ablation temperature and lesion volume during temperature-controlled radiofrequency ablation (RFA) of liver tumor by parameter sensitivity analysis.

METHODS:

The finite element method (FEM) has been used to establish the simulation model of RFA temperature field, and the sensitivity of the tissue parameters has been analyzed. The effects of six parameters have been taken into account, including the thermal specific capacity (Cp), the thermal conductivity (k), the electrical conductivity (Sigma), the density (rho), the dielectric constant (Epsilon) and the resistance (R). The simulation processes based on different parameter values have been accomplished with Comsol Multiphysics software, and the sensitivity parameters have been obtained utilizing the variance contribution rate (SS%) or the main effects.

RESULTS:

It was found that the ablation temperature and lesion volume increased with increasing the values of Rand Sigma, but was a reverse situation for Cp and rho. Besides, the influence of k on ablation volume was relatively small and Epsilon had a negligible effect on ablation temperature.

CONCLUSIONS:

It is concluded that these parameter sensitivity results can provide scientific and reliable reference for the specificity analysis of the RF ablation models.

Optimization of an Endoscopic Radiofrequency Ablation Electrode

Radiofrequency ablation (RFA) is an increasingly used, minimally invasive, cancer treatment modality for patients who are unwilling or unable to undergo a major resective surgery. There is a need for RFA electrodes that generate thermal ablation zones that closely match the geometry of typical tumors, especially for endoscopic ultrasound-guided (EUS) RFA. In this paper, the procedure for optimization of an RFA electrode is presented. First, a novel compliant electrode design is proposed. Next, a thermal ablation model is developed to predict the ablation zone produced by an RFA electrode in biological tissue. Then, a multi-objective genetic algorithm is used to optimize two cases of the electrode geometry to match the region of destructed tissue to a spherical tumor of a specified diameter. This optimization procedure is then applied to EUS-RFA ablation of pancreatic tissue. For a target 2.5 cm spherical tumor, the optimal design parameters of the compliant electrode design are found for two cases. Cases 1 and 2 optimal solutions filled 70.9% and 87.0% of the target volume as compared to only 25.1% for a standard straight electrode. The results of the optimization demonstrate how computational models combined with optimization can be used for systematic design of ablation electrodes. The optimization procedure may be applied to RFA of various tissue types for systematic design of electrodes for a specific target shape.

Liquid metal bath as conformable soft electrodes for target tissue ablation in radio-frequency ablation therapy

BACKGROUND

Radio-frequency ablation has been an important physical method for tumor hyperthermia therapy. The conventional rigid electrode boards are often uncomfortable and inconvenient for performing surgery on irregular tumors, especially for those tumors near the joints, such as ankles, knee-joints or other facets like finger joints.

MATERIAL AND METHODS

We proposed and demonstrated a highly conformable tumor ablation strategy through introducing liquid metal bath as conformable soft electrodes. Different heights of liquid metal bath electrodes were adopted to perform radio-frequency ablation on targeted tissues. Temperature and ablation area were measured to compare the ablation effect with plate metal electrodes.

RESULTS

The recorded temperature around the ablation electrode was almost twice as high as that with the plate electrode and the effective ablated area was 2-3 fold larger in all the mimicking situations of bone tumors, span-shaped or round-shaped tumors. Another unique feature of the liquid metal electrode therapy is that the incidence of heat injury was reduced, which is a severe accident that can occur during the treatment of irregular tumors with plate metal boards.

CONCLUSIONS

The present method suggests a new way of using soft liquid metal bath electrodes for targeted minimally invasive tumor ablation in future clinical practice.

Performance of radiofrequency ablation used for metastatic spinal tumor: Numerical approach

Surgical treatment of spine metastases follows only local anatomical and biomechanical objectives. Few cases of actual solitary metastases are rather exceptional, while removal of these metastases and the primary tumor may help to eradicate the process. The aim of our subsequent numerical simulations was to find out the temperature distribution and the volume lesion in a spinal tumor. For this purpose, the parametric three-dimensional numerical model was developed. It was shown that by finite element modeling approach not only the temperature distribution but even the resulted cavity may be estimated. The numerical approach was shown as a strong tool in surgery planning.