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. A model of an IC electrode was used to compare the ICW electrode performance and the computational results with the experimental results. 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 modelled during RFA.

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. The computer results obtained by programming voltage pulses were compared with current pulses. RESULTS: The differences between voltage and current pulses 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 the 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.

Artificial Neural Networks to Optimize Oil-in-Water Emulsion Stability with Orange By-Products.

The use of artificial neural networks (ANNs) is proposed to optimize the formulation of stable oil-in-water emulsions (oil 6% w/w) with a flour made from orange by-products (OBF), rich in pectins (21 g/100 g fresh matter), in different concentrations (0.95, 2.38, and 3.40% w/w), combined with or without soy proteins (0.3 and 0.6% w/w). Emulsions containing OBF were stable against coalescence and flocculation (with 2.4 and 3.4% OBF) and creaming (3.4% OBF) for 24 h; the droplets' diameter decreased up to 44% and the viscosity increased up to 37% with higher concentrations of OBF. With the protein addition, the droplets' diameter decreased by up to 70%, and flocculation increased. Compared with emulsions produced with purified citrus pectins (0.2 and 0.5% w/w), OBF emulsions exhibited up to 32% lower viscosities, 129% larger droplets, and 45% smaller Z potential values. Optimization solved with ANNs minimizing the droplet size and the emulsion instability resulted in OBF and protein concentrations of 3.16 and 0.14%, respectively. The experimental characteristics of the optimum emulsion closely matched those predicted by ANNs demonstrating the usefulness of the proposed method.

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. METHODS: We make experimental and computer models. The thermal effects of laser irradiation on the nc-YSZ samples were evaluated upon registering the induced temperature changes by means of thermal imaging. The computer models try to mimic the experimental models using a similar geometry, reproducing the physical situation by a couple thermal-optical problem and adjusting the main parameters from the experimental results. RESULTS: Experimental and computational coincides in results: Temperatures at the bottom surface of the implant does not exceed those which produce thermal damage. The quantitative comparison between experimental and computational models show that differences in results are under a reasonable value of 5% and qualitatively we observe a similar behavior. The results provide optimum values for the thermal-optical nc-YSZ parameters considering a linear and exponential relationship with temperature for the absorption coefficient: The thermal conductivity is k = 2.13 W/m·K and the absorption coefficient α varies from 426 to 526 m-1 with the linear relationship, and k = 2.04 W/m·K and α ∈ [433,502] m-1 with the exponential. The reflection coefficient is R = 19% in both cases. CONCLUSIONS: The temperatures achieved in the nc-YSZ during the laser irradiation are suitable for biomedical applications. The combination of experimental and computational models contributes to build a clinically oriented model with the thermal-optical parameters values stablished and to determine their influence in results. Specifically, the absorption coefficient of the nc-YSZ samples is the most influent parameter in the obtained temperatures. Moreover, this combination provides a method to evaluate the relevant thermal-optical parameters of nc-YSZ samples obtained with different manufacturing processes.

Intensification of the convective drying process of Salvia officinalis: Modeling and optimization.

The current study deals with an innovation in the hot air convective drying process consisting of the application of two consecutive drying steps. Temperatures ranging between 60 and 80 ℃ for times between 200 and 600 s were applied for the first stage, and from 40 to 80 ℃ for the second stage. Salvia officinalis, an aromatic, medicinal Mediterranean plant with remarkable antioxidant properties, was selected for this study. A management of the process regarding the antioxidant capacity of S. officinalis extracts and energy consumption was carried out: (i) artificial neural networks were applied to model the evolution of the antioxidant capacity and moisture content of the product in the drying process; (ii) a genetic algorithm and a multiobjective genetic algorithm were selected to optimize the drying process, considering the antioxidant capacity and/or the energy consumption in the objective function. The results showed that the optimum values depended, logically, on the controllable variables values (hot air temperatures and drying times), but also on the uncontrollable variable values (room air temperature and relative humidity and the product's initial mass and moisture content).

Optimisation of the addition of carrot dietary fibre to a dry fermented sausage (sobrassada) using artificial neural networks.

An optimisation problem was formulated to maximise the amount of carrot dietary fibre (CDF) in a dry fermented sausage, while maintaining product quality, by using 0-12% CDF as the decision variable, and limiting values of several physico-chemical and textural parameters (moisture content, water activity, pH, colour, non-protein nitrogen, free fatty acid, compression work and hardness) as constraints. The evolution of each quality parameter during the ripening process was estimated by developing a multi-layer feed forward artificial neural network (ANN), taking into consideration the CDF concentration and the ripening time as independent variables. Results indicate an optimum CDF concentration of 4.9% with a good correlation between experimental and estimated values (mean relative error≤3.35%).