Electrical-thermal performance of a cooled RF applicator for hepatic ablation with additional distant infusion of hypertonic saline:<i>In vivo</i>study and preliminary computer modeling

Purpose: To develop computer models to mimic the impedance-controlled pulsing protocol implemented in 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-minute RFA was modeled 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 and considering clamping) and ex vivo (at 21ºC) conditions.The computer results obtained by programming voltage pulses were compared with current pulses.Results: The differences between voltage and current pulses protocol were noticeable: using current instead of voltage allows larger coagulation zones to be created, due to the higher energy applied by current pulses. If voltage pulses are employed, the model can accurately predict number of roll-offs, although the waveform of the applied power is clearly not realistic. If current voltages are employed, the applied power waveform matches well with those reported experimentally, but there are significantly fewer roll-offs. Our computer results were overall into the ranges of experimental ones. Conclusions:The proposed models reproduce reasonably well the electrical-thermal performance and coagulation zone size obtained during an impedance-controlled pulsing protocol.

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“…This last value is more in agreement with those obtained in experimental studies (see Fig. 4 in [27] and Fig. 2 in [26]).…”

Section: Comparison Between Current Pulses and Voltage Pulsessupporting

confidence: 92%

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

Trujillo

Bon

Rivera

et al. 2016

International Journal of Hyperthermia

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“…We initially considered (37ºC)=0.19 S/m for the liver tissue without the presence of saline. This value was in the range proposed for liver electrical conductivity at 37ºC [29] and matches with initial experimentally observed impedance values [16]. However, as liver increases with the presence of saline [16], we assessed the impact of using higher values for (37ºC) in the tissue zone affected by saline.…”

Section: ) Conductivity Modificationmentioning

confidence: 76%

“…In a previous computational study we modeled the hypertonic saline infusion simply with a convective term in the governing equation and an electrical conductivity function that varied with distance from the infusion point [16]. Although the results reproduced a delay in roll-off, this was never totally absent.…”

Section: Introductionmentioning

confidence: 93%

“…It is thought that rehydration could play a relevant role, i.e. infusion could compensate for desiccation by the continuous supply of liquid to the zone in which vaporization occurs, and consequently keep impedance low for a longer period, thus allowing the creation of larger coagulation zones [15,16]. Two other effects could also influence the capacity of ICW electrodes to create larger coagulation zones: 1) the increase in tissue electrical conductivity by infused saline and 2) the thermal convection produced by the flow of saline.…”

Section: Introductionmentioning

confidence: 99%

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

Trujillo

Bon

Berjano

2017

International Journal of Hyperthermia

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Results: Rehydration and increased electrical conductivity were responsible for an increase in coagulation zone size and a delay (or absence) in the occurrence of abrupt increases in electrical impedance (roll-off). While the increased electrical conductivity had a remarkable effect on enlarging the coagulation zone (an increase of 0.74 cm for differences in electrical conductivity of 0.31 S/m), rehydration considerably affected the delay in roll-off, which, in fact, was absent with a sufficiently high rehydration level. In contrast, thermal convection had an insignificant effect for the flow rates considered (0.05 and 1 mL/min). Conclusions:Computer results suggest that rehydration and increased electrical conductivity were mainly responsible for the absence of roll-off and increased size of the coagulation zone, respectively, and in combination allow the thermal and electrical performance of ICW electrodes to be modeled during RFA.

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“…RFA electrodes, generators and treatment protocols are constantly being improved to increase the ablation diameter [4][5][6][7][8][9][10][11][12][13][14][15][16]. Unfortunately, attention to reliability of RFA performance is lagging behind.…”

Section: Introductionmentioning

confidence: 99%

Bipolar radiofrequency ablation with 2 × 2 electrodes as a building block for matrix radiofrequency ablation:Ex vivoliver experiments and finite element method modelling

Mulier

Jiang

Jamart

et al. 2015

International Journal of Hyperthermia

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Purpose: Size and geometry of the ablation zone obtained by currently available radiofrequency (RF) electrodes is highly variable. Reliability might be improved by matrix radiofrequency ablation (MRFA), in which the whole tumour volume is contained within a cage of x Â y parallel electrodes. The aim of this study was to optimise the smallest building block for matrix radiofrequency ablation: a recently developed bipolar 2 Â 2 electrode system. Materials and methods: In ex vivo bovine liver, the parameters of the experimental set-up were changed one by one. In a second step, a finite element method (FEM) modelling of the experiment was performed to better understand the experimental findings. Results:The optimal power to obtain complete ablation in the shortest time was 50-60 W. Performing an ablation until impedance rise was superior to ablation for a fixed duration. Increasing electrode diameter improved completeness of ablation due to lower temperature along the electrodes. A chessboard pattern of electrode polarity was inferior to a row pattern due to an electric field void in between the electrodes. Variability of ablation size was limited. The FEM correctly simulated and explained the findings in ex vivo liver. Conclusions: These experiments and FEM modelling allowed a better insight in the factors influencing the ablation zone in a bipolar 2 Â 2 electrode RF system. With optimal parameters, complete ablation was obtained quickly and with limited variability. This knowledge will be useful to build a larger system with x Â y electrodes for MRFA.

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Electrical-thermal performance of a cooled RF applicator for hepatic ablation with additional distant infusion of hypertonic saline:In vivostudy and preliminary computer modeling

Abstract: The hybrid applicator produces fewer roll-off episodes than the Cool-tip electrode and creates larger coagulation volumes with larger transverse diameters.

Cited by 14 publications

References 18 publications

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

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

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

Bipolar radiofrequency ablation with 2 × 2 electrodes as a building block for matrix radiofrequency ablation:Ex vivoliver experiments and finite element method modelling

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