Impact of Power and Time in Hepatic Microwave Ablation: Effect of Different Energy Delivery Schemes.

Microwave ablation often involves the use of continuous energy-delivery protocols with a fixed power and time. To achieve larger ablation zones, a range of protocols and power levels have been studied in experimental studies. The objective of the present study was to develop and experimentally evaluate the performance of a coupled computational electromagnetic-bioheat transfer model of 2.

Comparison of two radiofrequency-based hemostatic devices: saline-linked bipolar cooled-electrode monopolar.

Purpose: To characterize the coagulation zones created by two radiofrequency (RF)-based hemostatic devices: one comprised an internally cooled monopolar electrode and the other comprised externally irrigated bipolar electrodes (saline-linked).

Materials And Methods: RF-induced coagulation zones were created on and porcine models. Computer modeling was used to determine the RF power distribution in the saline-linked device.

Experimental and computational model approach to assess the photothermal effects in transparent nanocrystalline yttria stabilized zirconia cranial implant.

Background And Objective: In the last few years, we have been exploring the use of transparent nanocrystalline yttria-stabilized zirconia (nc-YSZ) ceramics as a biomedical transparent cranial implant, referred as the "Window to the Brain" (WttB). The WttB aims at providing chronical optical access to the brain for diagnostics and therapeutic procedures and it has shown to provide an effective means to obtain enhanced results from optical imaging techniques. The objective of this work is to explore the photothermal effects of the Wttb produced when it is irradiated by a laser source.

Microwave versus radiofrequency ablation for the treatment of liver malignancies: a randomized controlled phase 2 trial.

Microwave (MWA) and radiofrequency ablation (RFA) are main ablative techniques for hepatocellular carcinoma (HCC) and colorectal liver metastasis (MT). This randomized phase 2 clinical trial compares the effectiveness of MWA and RFA as well as morphology of corresponding ablation zones. HCC and MT patients with 1.

Mathematical modeling of microwave liver ablation with a variable-porosity medium approach.

Background And Objectives: Thermal ablation of tumors plays a key role to fight cancer, since it is a minimally invasive treatment which involves some advantages compared to surgery and chemotherapy, such as shorter hospital stays and consequently lower costs, along with minor side effects. In this context, computational modeling of heat transfer during thermal ablation is relevant to accurately predict the obtained ablation zone in order to avoid tumor recurrence risk caused by incomplete ablation, and the same time to save the surrounding healthy tissue. The aim of this work is to develop a more realistic porous media-based mathematical model to simulate a microwave thermal ablation (MWA) of an in vivo liver tumor surrounded by healthy tissue.

Short pulsed microwave ablation: computer modeling and 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 and conditions.

Pennes' bioheat equation vs. porous media approach in computer modeling of radiofrequency tumor ablation.

The objective of this study was to compare three different heat transfer models for radiofrequency ablation of in vivo liver tissue using a cooled electrode and three different voltage levels. The comparison was between the simplest but less realistic Pennes' equation and two porous media-based models, i.e.

Two-compartment mathematical modeling in RF tumor ablation: New insight when irreversible changes in electrical conductivity are considered.

The objective was to explore variations of temperature distribution and coagulation zone size computed by a two-compartment radiofrequency ablation (RFA) model when including simultaneously reversible changes in the tissue electrical conductivity (σ) due to temperature and irreversible changes due to thermal coagulation. Two-compartment (tumor and healthy tissue) models were built and simulated. Reversible change of σ was modeled by a piecewise function characterized by increments of +1.

How large is the periablational zone after radiofrequency and microwave ablation? Computer-based comparative study of two currently used clinical devices.

Purpose: To compare the size of the coagulation (CZ) and periablational (PZ) zones created with two commercially available devices in clinical use for radiofrequency (RFA) and microwave ablation (MWA), respectively.

Methods: Computer models were used to simulate RFA with a 3-cm Cool-tip applicator and MWA with an Amica-Gen applicator. The Arrhenius model was used to compute the damage index ().

Development of a catheter-based technique for endoluminal radiofrequency sealing of pancreatic duct.

Endoluminal sealing of the pancreatic duct by glue or sutures facilitates the management of the pancreatic stump. Our objective was to develop a catheter-based alternative for endoluminal radiofrequency (RF) sealing of the pancreatic duct. We devised a novel RF ablation technique based on impedance-guided catheter pullback.

Effect of applied voltage, duration and repetition frequency of RF pulses for pain relief on temperature spikes and electrical field: a computer modelling study.

Background: The thermal and electrical effects of pulsed radiofrequency (PRF) for pain relief can be controlled by modifying the characteristics of the RF pulses applied. Our goal was to evaluate the influence of such modifications on the thermal and electric performance in tissue.

Methods: A computational model was developed to compare the temperature and electric field time courses in tissue between a standard clinical protocol (45 V pulses, 20 ms duration, 2 Hz repetition frequency) and a new protocol (55 V pulses, 5 ms duration, 5 Hz repetition frequency) with a higher applied electric field but a smaller impact on temperature alterations in tissue.

Computational modelling of internally cooled wet (ICW) electrodes for radiofrequency ablation: impact of rehydration, thermal convection and electrical conductivity.

Purpose: (1) To analyse rehydration, thermal convection and increased electrical conductivity as the three phenomena which distinguish the performance of internally cooled electrodes (IC) and internally cooled wet (ICW) electrodes during radiofrequency ablation (RFA), (2) Implement a RFA computer model with an ICW which includes these phenomena and (3) Assess their relative influence on the thermal and electrical tissue response and on the coagulation zone size.

Methods: A 12-min RFA in liver was modelled using an ICW electrode (17 G, 3 cm tip) by an impedance-control pulsing protocol with a constant current of 1.5 A.

How coagulation zone size is underestimated in computer modeling of RF ablation by ignoring the cooling phase just after RF power is switched off.

All the numerical models developed for radiofrequency ablation so far have ignored the possible effect of the cooling phase (just after radiofrequency power is switched off) on the dimensions of the coagulation zone. Our objective was thus to quantify the differences in the minor radius of the coagulation zone computed by including and ignoring the cooling phase. We built models of RF tumor ablation with 2 needle-like electrodes: a dry electrode (5 mm long and 17G in diameter) with a constant temperature protocol (70°C) and a cooled electrode (30 mm long and 17G in diameter) with a protocol of impedance control.

Computer modelling of an impedance-controlled pulsing protocol for RF tumour ablation with a cooled electrode.

Purpose: To develop computer models to mimic the impedance-controlled pulsing protocol implemented in radiofrequency (RF) generators used for clinical practice of radiofrequency ablation (RFA), and to assess the appropriateness of the models by comparing the computer results with those obtained in previous experimental studies.

Methods: A 12-min RFA was modelled using a cooled electrode (17G, 3 cm tip) inserted in hepatic tissue. The short (transverse) diameter of the coagulation zone was assessed under in vivo (with blood perfusion (BP) and considering clamping) and ex vivo (at 21 °C) conditions.

Can Fat Deposition After Myocardial Infarction Alter the Performance of RF Catheter Ablation of Scar-Related Ventricular Tachycardia?: Results from a Computer Modeling Study.

Introduction: The outcomes of catheter ablation of scar-mediated ventricular tachycardia (VT) remain far from perfect. The presence of fat as a component of the underlying substrate for scar-mediated VT could be relevant since this entity can seriously impede the passage of RF current due to its low electrical conductivity.

Methods And Results: Computer models of RF ablation were built in order to investigate the means by which the spatial heterogeneity of different tissues represented within the ventricular infarct zone, including the viable myocardium, fibrous tissue, and fat, could influence temperature distributions during RF ablation.

Computer modelling of RF ablation in cortical osteoid osteoma: Assessment of the insulating effect of the reactive zone.

Purpose: The aim was to study by computer simulations the insulating role of the reactive zone surrounding a cortical osteoid osteoma (OO) in terms of electrical and thermal performance during radiofrequency ablation (RFA).

Material And Methods: We modelled a cortical OO consisting of a nidus (10 mm diameter) enclosed by a reactive zone. The OO was near a layer of cortical bone 1.

Computer modeling and ex vivo experiments with a (saline-linked) irrigated electrode for RF-assisted heating.

Background: Externally irrigated radiofrequency (RF) electrodes have been widely used to thermally ablate tumors in surface tissue and to thermally coagulate the transection plane during a surgical resection. As far as we know, no mathematical model has yet been developed to study the electrical and thermal performance of these electrodes, especially the role of the saline layer that forms around the electrode.

Methods: Numerical models of a TissueLink device model DS3.

Radiofrequency cardiac ablation with catheters placed on opposing sides of the ventricular wall: computer modelling comparing bipolar and unipolar modes.

Purpose: The aim of this study was to compare the efficacy of bipolar (BM) vs. unipolar (UM) mode of radiofrequency ablation (RFA) in terms of creating transmural lesions across the interventricular septum (IVS) and ventricular free wall (VFW).

Materials And Methods: We built computational models to study the temperature distributions and lesion dimensions created by BM and UM on IVS and VFW during RFA.

Could the heat sink effect of blood flow inside large vessels protect the vessel wall from thermal damage during RF-assisted surgical resection?

Purpose: To assess by means of computer simulations whether the heat sink effect inside a large vessel (portal vein) could protect the vessel wall from thermal damage close to an internally cooled electrode during radiofrequency (RF)-assisted resection.

Methods: First,in vivo experiments were conducted to validate the computational model by comparing the experimental and computational thermal lesion shapes created around the vessels. Computer simulations were then carried out to study the effect of different factors such as device-tissue contact, vessel position, and vessel-device distance on temperature distributions and thermal lesion shapes near a large vessel, specifically the portal vein.

Review of the mathematical functions used to model the temperature dependence of electrical and thermal conductivities of biological tissue in radiofrequency ablation.

Purpose: Although theoretical modelling is widely used to study different aspects of radiofrequency ablation (RFA), its utility is directly related to its realism. An important factor in this realism is the use of mathematical functions to model the temperature dependence of thermal (k) and electrical (σ) conductivities of tissue. Our aim was to review the piecewise mathematical functions most commonly used for modelling the temperature dependence of k and σ in RFA computational modelling.

Can electroporation previous to radiofrequency hepatic ablation enlarge thermal lesion size? A feasibility study based on theoretical modelling and in vivo experiments.

Purpose: The aim of this study was to assess the feasibility of a hybrid ablative technique based on applying electroporation (EP) pulses just before conducting radiofrequency ablation (RFA). The rationale was that the EP-induced reduction in blood perfusion could be sufficient to reduce the thermal sink effect and hence to increase the coagulation volume in comparison to that created exclusively by RFA.

Materials And Methods: A modelling study and in vivo experimental study were used.

Feasibility study of an internally cooled bipolar applicator for RF coagulation of hepatic tissue: experimental and computational study.

Purpose: To study the capacity of an internally cooled radiofrequency (RF) bipolar applicator to create sufficiently deep thermal lesions in hepatic tissue.

Materials And Methods: Three complementary methodologies were employed to check the electrical and thermal behaviour of the applicator under test. The experimental studies were based on excised bovine (ex vivo study) and porcine liver (in vivo study) and the theoretical models were solved by means of the finite element method (FEM).

Mathematical models based on transfer functions to estimate tissue temperature during RF cardiac ablation in real time.

Radiofrequency cardiac ablation (RFCA) has been used to treat certain types of cardiac arrhythmias by producing a thermal lesion. Even though a tissue temperature higher than 50ºC is required to destroy the target, thermal mapping is not currently used during RFCA. Our aim was thus to develop mathematical models capable of estimating tissue temperature from tissue characteristics acquired or estimated at the beginning of the procedure (electrical conductivity, thermal conductivity, specific heat and density) and the applied voltage at any time.

Relationship between roll-off occurrence and spatial distribution of dehydrated tissue during RF ablation with cooled electrodes.

Purpose: To study the relationship between roll-off (sudden increase in impedance) and spatial distribution of dehydrated tissue during RF ablation using a cooled electrode (temperatures around 100°C).

Methods: We used a double approach: (1) theoretical modelling based on the finite element method, and (2) 20 ablations using an experimental study on ex vivo excised bovine liver in which we measured impedance progress and temperature at three points close to the electrode surface: 0.5 (T1), 1.

Applicator for RF thermokeratoplasty: feasibility study using theoretical modeling and ex vivo experiments.

Radiofrequency (RF) thermokeratoplasty uses RF currents to alter the curvature of the cornea by means of thermal lesions. An RF applicator which combined a microkeratome suction ring and a circular electrode was designed with the aim of creating circular thermal lesions in a predictable, uniform and safe way. An experimental study was conducted on ex vivo porcine eyes.