An Analytical Solution for Radiofrequency Ablation with a Cooled Cylindrical Electrode

[EN] We present an analytical solution to the electrothermal mathematical model of radiofrequency ablation of biological tissue using a cooled cylindrical electrode. The solution presented here makes use of the method of separation of variables to solve the problem. Green's functions are used for the handling of nonhomogeneous terms, such as effect of electrical currents circulation and the nonhomogeneous boundary condition due to cooling at the electrode surface. The transcendental equation for determination of eigenvalues of this problem is solved using Newton's method, and the integrals that appear in the solution of the problem are obtained by Simpson's rule. The solution obtained here has the possibility of handling different functional dependencies of the source term and nonhomogeneous boundary condition. The solution provides a tool to understand the physics of the problem, as it shows how the solution depends on different parameters, to provide mathematical tools for the design of surgical procedures and to validate other modeling techniques, such as the numerical methods that are frequently used to solve the problem.This work was supported by the Universidad Autonoma de San Luis Potosi (Mexico), which granted Ricardo Romero-Mendez a sabbatical leave to do research in the field of biomedical engineering, and the Government of Spain through the "Plan Estatal de Investigacion, Desarrollo e Innovacion Orientada a los Retos de la Sociedad" (Grants TEC 2014-52383-C3-R and TEC 2014-52383-C3-1-R).Romero-Méndez, R.; Berjano, E. (2017). An Analytical Solution for Radiofrequency Ablation with a Cooled Cylindrical Electrode. Mathematical Problems in Engineering. (9021616):1-12. doi:10.1155/2017/9021616S112902161

Radiofrequency ablation combined with conductive fluid-based dopants (saline normal and colloidal gold): computer modeling and ex vivo experiments

[EN] Background: The volume of the coagulation zones created during radiofrequency ablation (RFA) is limited by the appearance of roll-off. Doping the tissue with conductive fluids, e.g., gold nanoparticles (AuNPs) could enlarge these zones by delaying roll-off. Our goal was to characterize the electrical conductivity of a substrate doped with AuNPs in a computer modeling study and ex vivo experiments to investigate their effect on coagulation zone volumes. Methods: The electrical conductivity of substrates doped with normal saline or AuNPs was assessed experimentally on agar phantoms. The computer models, built and solved on COMSOL Multiphysics, consisted of a cylindrical domain mimicking liver tissue and a spherical domain mimicking a doped zone with 2, 3 and 4 cm diameters. Ex vivo experiments were conducted on bovine liver fragments under three different conditions: non-doped tissue (ND Group), 2 mL of 0.9% NaCl (NaCl Group), and 2 mL of AuNPs 0.1 wt% (AuNPs Group). Results: The theoretical analysis showed that adding normal saline or colloidal gold in concentrations lower than 10% only modifies the electrical conductivity of the doped substrate with practically no change in the thermal characteristics. The computer results showed a relationship between doped zone size and electrode length regarding the created coagulation zone. There was good agreement between the ex vivo and computational results in terms of transverse diameter of the coagulation zone. Conclusions: Both the computer and ex vivo experiments showed that doping with AuNPs can enlarge the coagulation zone, especially the transverse diameter and hence enhance sphericity.This work was supported by the National Council of Science and Technology (CONACYT, Mexico) through a scholarship grant to Dora Luz Castro-Lopez, CVU Registration No. 446604; and by the Spanish Ministerio de Ciencia, Innovacion y Universidades under the "Plan Estatal de Investigacion, Desarrollo e Innovacion Orientada a los Retos de la Sociedad", Grant No "RTI2018-094357-B-C21"Castro-López, DL.; Berjano, E.; Romero-Méndez, R. (2021). Radiofrequency ablation combined with conductive fluid-based dopants (saline normal and colloidal gold): computer modeling and ex vivo experiments. BioMedical Engineering OnLine. 20:1-20. https://doi.org/10.1186/s12938-020-00842-8S12020Zhu F, Rhim H. Thermal ablation for hepatocellular carcinoma: what’s new in 2019. 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Gold nanoparticles and radiofrequency in experimental models for hepatocellular carcinoma. Nanomedicine. 2014;10(6):1121–30.Xie H, Wang J, Xi T, Liu Y. Thermal conductivity of suspensions containing nanosized SiC particles. Int J Thermophys. 2002;23:571–80.Yull Park J, Young Park C, Min Lee J. Estimation of saline-mixed tissue conductivity and ablation lesion size. Comput Biol Med. 2013;43(5):504–12.Abdelhalim MAK, Mady MM, Ghannam MM. Dielectric constant, electrical conductivity and relaxation time measurements of different gold nanoparticle sizes. Int J Phys Sci. 2011;6(23):5487–91.Zorbas G, Samaras T. Parametric study of radiofrequency ablation in the clinical practice with the use of two-compartment numerical models. Electromagn Biol Med. 2013;32(2):236–43.Zhang B, Moser MA, Zhang EM, Luo Y, Zhang H, Zhang W. Study of the relationship between the target tissue necrosis volume and the target tissue size in liver tumours using two-compartment finite element RFA modelling. Int J Hyperthermia. 2014;30(8):593–602.Francica G. Needle track seeding after radiofrequency ablation for hepatocellular carcinoma: prevalence, impact, and management challenge. J Hepatocell Carcinoma. 2017;20(4):23–7.Ji Q, Xu Z, Liu G, Lin M, Kuang M, Lu M. Preinjected fluids do not benefit microwave ablation as those in radiofrequency ablation. Acad Radiol. 2011;18(9):1151–8.Goldberg SN, Stein MC, Gazelle GS, Sheiman RG, Kruskal JB, Clouse ME. Percutaneous radiofrequency tissue ablation: optimization of pulsed-radiofrequency technique to increase coagulation necrosis. J Vasc Interv Radiol. 1999;10(7):907–16.Solazzo SA, Ahmed M, Liu Z, Hines-Peralta AU, Goldberg SN. High-power generator for radiofrequency ablation: larger electrodes and pulsing algorithms in bovine ex vivo and porcine in vivo settings. Radiology. 2007;242(3):743–50.Goldberg SN, Ahmed M, Gazelle GS, Kruskal JB, Huertas JC, Halpern EF, Oliver BS, Lenkinski RE. Radio-frequency thermal ablation with NaCl solution injection: effect of electrical conductivity on tissue heating and coagulation-phantom and porcine liver study. Radiology. 2001;219(1):157–65.Trujillo M, Bon J, Berjano E. Computational modelling of internally cooled wet (ICW) electrodes for radiofrequency ablation: impact of rehydration, thermal convection and electrical conductivity. Int J Hyperthermia. 2017;33(6):624–34.Gillams AR, Lees WR. CT mapping of the distribution of saline during radiofrequency ablation with perfusion electrodes. Cardiovasc Intervent Radiol. 2005;28(4):476–80.Takata AN, Zaneveld L, Richter W. Laser-induced thermal damage of skin (Rep. SAM-TR-77–38). USAF School Aerospace Medicine, Brooks Air Force Base, Texas. 1977: 22−3.Burdío F, Berjano E, Millan O, Grande L, Poves I, Silva C, de la Fuente MD, Mojal S. CT mapping of saline distribution after infusion of saline into the liver in an ex vivo animal model. How much tissue is actually infused in an image-guided procedure? Phys Med. 2013;29(2):188–95.Abraham JP, Sparrow EM. A thermal-ablation bioheat model including liquid-to-vapor phase change, pressure- and necrosis-dependent perfusion, and moisture-dependent properties. Int J Heat Mass Transfer. 2007;50:2537–44.Pätz T, Kröger T, Preusser T, Simulation of radiofrequency ablation including water evaporation, IFMBE Proceedings, 25/IV:1287–90, 2009.https://www.engineeringtoolbox.com/specific-heat-capacity-water-d_660.html (accessed March 15, 2020).Carson JK. Review of effective thermal conductivity models for foods. Int J Refrigeration. 2006;29(6):958–67.Cruz RCD, Reinshagen J, Oberacker R, Segadães AM. Electrical conductivity and stability of concentrated aqueous alumina suspensions. J Colloid Interface Sci. 2005;286:579–88.Trujillo M, Bon J, Rivera MJ, Burdio F, Berjano E. Computer modelling of an impedance-controlled pulsing protocol for RF tumour ablation with a cooled electrode. Int J Hyperthermia. 2016;32:931–9

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

[EN] 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 (sigma) due to temperature and irreversible changes due to thermal coagulation. Two-compartment (tumor and healthy tissue) models were built and simulated. Reversible change of sigma was modeled by a piecewise function characterized by increments of +1.5%/degrees C up to 100 degrees C, and a 100 times smaller value from 100 degrees C onwards. Irreversible changes of sigma were modeled using an Arrhenius model. We assumed that both tumor and healthy tissue had a different initial sigma value (as suggested by the experimental data in the literature) and tended towards a common value as thermal damage progressed (necrotized tissue). We modeled a constant impedance protocol based on 90 V pulses voltage and three tumor diameters (2, 3 and 4 cm). Computer simulations showed that the differences between both models were only 0.1 and 0.2 cm for axial and transverse diameters, respectively, and this small difference was reflected in the similar temperature distributions computed by both models. In view of the available experimental data on changes of electrical conductivity in tumors and healthy tissue during heating, our results suggest that irreversible changes in electrical conductivity do not have a significant impact on coagulation zone size in two-compartment RFA models.This work was supported by the National Council of Science and Technology (CONACYT, Mexico) through a scholarship grant to Dora Luz Castro-Lopez, CVU registration No 446604; and by the Spanish Ministerio de Ciencia, Innovacion y Universidades under "Programma Estatal de I+D+i Orientada a los Retos de la Sociedad", Grant No "RTI2018-094357-B-C21".Castro-López, DL.; Trujillo Guillen, M.; Berjano, E.; Romero-Mendez, R. (2020). Two-compartment mathematical modeling in RF tumor ablation: New insight when irreversible changes in electrical conductivity are considered. Mathematical Biosciences and Engineering. 17(6):7980-7993. https://doi.org/10.3934/mbe.2020405S798079931762. D. Haemmerich, L. Chachati, A. S. Wright, D. M. Mahvi, F. T. Lee Jr, J. G. Webster, Hepatic radiofrequency ablation with internally cooled probes: Effect of coolant temperature on lesion size, IEEE Trans. Biomed. Eng., 50 (2003), 493-500.4. Z. Liu, S. M. Lobo, S. Humphries, C. Horkan, S. A. Solazzo, A. U. Hines-Peralta, et al., Radiofrequency tumor ablation: insight into improved efficacy using computer modeling, AJR Am. J. Roentgenol., 184 (2005), 1347-1352.5. S. M. Lobo, Z. J. Liu, N. C. Yu, S. Humphries, M. Ahmed, E. R. Cosman, et al., RF tumour ablation: computer simulation and mathematical modelling of the effects of electrical and thermal conductivity, Int. J. Hyperth., 21 (2005), 199-213.9. D. Haemmerich, D. J. Schutt, RF ablation at low frequencies for targeted tumor heating: In vitro and computational modeling results, IEEE Trans. Biomed. Eng., 58 (2011), 404-410.17. M. Pop, A. Molckovsky, L. Chin, M. C. Kolios, M. A. Jewett, M. D. Sherar, Changes in dielectric properties at 460 kHz of kidney and fat during heating: importance for radio-frequency thermal therapy, Phys. Med. Biol., 48 (2003), 2509-2525.18. U. Zurbuchen, C. Holmer, K. S. Lehmann, T. Stein, A. Roggan, C. Seifarth, et al., Determination of the temperature-dependent electric conductivity of liver tissue ex vivo and in vivo: Importance for therapy planning for the radiofrequency ablation of liver tumours, Int. J. Hyperth., 26 (2010), 26-33.19. E. G. Macchi, M. Gallati, G. Braschi, E. Persi, Dielectric properties of RF heated ex vivo porcine liver tissue at 480 kHz: measurements and simulations, J. Phys. D Appl. Phys., 47 (2014), 485401.21. E. Ewertowska, R. Quesada, A. Radosevic, A. Andaluz, X. Moll, F. G. Arnas, et al., A clinically oriented computer model for radiofrequency ablation of hepatic tissue with internally cooled wet electrode, Int. J. Hyperth., 35 (2019), 194-204.30. M. Qiu, A. Singh, D. Wang, J. Qu, M. Swihart, H. Zhang, P. N. Prasad, Biocompatible and biodegradable inorganic nanostructures for nanomedicine: Silicon and black phosphorus, Nano Today, 25 (2019), 135-155.33. A. Andreozzi, L. Brunese, M. Iasielllo, C. Tucci, G. P. Vanoli, Modeling heat transfer in tumors: A review of thermal therapies, Ann. Biomed. Eng., 47 (2019), 676-693

Analytical Solution for Electrical Problem Forced by a Finite-Length Needle Electrode: Implications in Electrostimulation

[EN] Needle electrodes, widely used in clinical procedures, are responsible for creating an electric field in the treated biological tissue. This is achieved by setting a constant voltage along the length of their metallic section. In accordance with Laplace's equation, the electric field is spatially non-uniform around the electrode surface. Mathematical modelling can provide useful information on the spatial distribution of electrical fields. Indeed, exact solutions for the electrical problem are indispensable for validating numerical codes. All the analytical models developed to date to solve the needle electrode electrical problem have been one-dimensional models, which assumed an electrode of infinite length. We here propose the first analytical solution based on a two-dimensional model that considers the real length of the electrode in which the Laplace equation is solved through the method of separation of variables, dealing with the nonhomogeneous source term and boundary conditions by Green's functions. On assuming a needle electrode of given length, the problem combines boundary conditions on the electrode boundary (of the first and second kind). Since this rules out using the Sturm-Liouville Theorem, the problem is decomposed into two different problems and the principle of superposition is used. The solution obtained can reproduce a reasonable electric field around the electrode, especially the edge effect characterized by an extremely high gradient around the electrode tip.This work was supported by the Universidad Autonoma de San Luis Potosi (Mexico), which granted R. Romero-Mendez who is on a sabbatical leave to do research in the field of biomedical engineering. This work was supported by the Spanish Ministerio de Ciencia, Innovacion y Universidades under "Programa Estatal de I+D+i Orientada a los Retos de la Sociedad" (grant number: RTI2018-094357-B-C21).Romero-Méndez, R.; Pérez-Gutiérrez, FG.; Oviedo-Tolentino, F.; Berjano, E. (2019). Analytical Solution for Electrical Problem Forced by a Finite-Length Needle Electrode: Implications in Electrostimulation. Mathematical Problems in Engineering. 1-10. https://doi.org/10.1155/2019/2404818S110Mulier, S., Miao, Y., Mulier, P., Dupas, B., Pereira, P., de Baere, T., … Ni, Y. (2005). Electrodes and multiple electrode systems for radiofrequency ablation: a proposal for updated terminology. European Radiology, 15(4), 798-808. doi:10.1007/s00330-004-2584-xMerrill, D. R., Bikson, M., & Jefferys, J. G. R. (2005). Electrical stimulation of excitable tissue: design of efficacious and safe protocols. Journal of Neuroscience Methods, 141(2), 171-198. doi:10.1016/j.jneumeth.2004.10.020Cogan, S. F. (2008). Neural Stimulation and Recording Electrodes. Annual Review of Biomedical Engineering, 10(1), 275-309. doi:10.1146/annurev.bioeng.10.061807.160518Kwon, H., Rutkove, S. B., & Sanchez, B. (2017). Recording characteristics of electrical impedance myography needle electrodes. Physiological Measurement, 38(9), 1748-1765. doi:10.1088/1361-6579/aa80acBurdío, F., Berjano, E. J., Navarro, A., Burdío, J. M., Güemes, A., Grande, L., … de Gregorio, M. A. (2007). RF tumor ablation with internally cooled electrodes and saline infusion: what is the optimal location of the saline infusion? BioMedical Engineering OnLine, 6(1), 30. doi:10.1186/1475-925x-6-30Zhang, B., Moser, M. A. J., Zhang, E. M., Luo, Y., Liu, C., & Zhang, W. (2016). A review of radiofrequency ablation: Large target tissue necrosis and mathematical modelling. Physica Medica, 32(8), 961-971. doi:10.1016/j.ejmp.2016.07.092Samoudi, A. M., Kampusch, S., Tanghe, E., Széles, J. C., Martens, L., Kaniusas, E., & Joseph, W. (2017). Numerical modeling of percutaneous auricular vagus nerve stimulation: a realistic 3D model to evaluate sensitivity of neural activation to electrode position. Medical & Biological Engineering & Computing, 55(10), 1763-1772. doi:10.1007/s11517-017-1629-7Samoudi, A. M., Vermeeren, G., Tanghe, E., Van Holen, R., Martens, L., & Josephs, W. (2016). Numerically simulated exposure of children and adults to pulsed gradient fields in MRI. Journal of Magnetic Resonance Imaging, 44(5), 1360-1367. doi:10.1002/jmri.25257Trujillo, M., Bon, J., José Rivera, M., Burdío, F., & Berjano, E. (2016). Computer modelling of an impedance-controlled pulsing protocol for RF tumour ablation with a cooled electrode. International Journal of Hyperthermia, 32(8), 931-939. doi:10.1080/02656736.2016.1190868Ewertowska, E., Mercadal, B., Muñoz, V., Ivorra, A., Trujillo, M., & Berjano, E. (2017). Effect of applied voltage, duration and repetition frequency of RF pulses for pain relief on temperature spikes and electrical field: a computer modelling study. International Journal of Hyperthermia, 34(1), 112-121. doi:10.1080/02656736.2017.1323122Zhang, B., Moser, M. A. J., Zhang, E. M., Luo, Y., & Zhang, W. (2016). A new approach to feedback control of radiofrequency ablation systems for large coagulation zones. International Journal of Hyperthermia, 33(4), 367-377. doi:10.1080/02656736.2016.1263365Haemmerich, D., Chachati, L., Wright, A. S., Mahvi, D. M., Lee, F. T., & Webster, J. G. (2003). Hepatic radiofrequency ablation with internally cooled probes: effect of coolant temperature on lesion size. IEEE Transactions on Biomedical Engineering, 50(4), 493-500. doi:10.1109/tbme.2003.809488López Molina, J. A., Rivera, M. J., & Berjano, E. (2017). Analytical transient-time solution for temperature in non perfused tissue during radiofrequency ablation. Applied Mathematical Modelling, 42, 618-635. doi:10.1016/j.apm.2016.10.044Romero-Méndez, R., & Berjano, E. (2017). An Analytical Solution for Radiofrequency Ablation with a Cooled Cylindrical Electrode. Mathematical Problems in Engineering, 2017, 1-12. doi:10.1155/2017/9021616Verhey, J., Nathan, N., Rienhoff, O., Kikinis, R., Rakebrandt, F., & D’Ambra, M. (2006). BioMedical Engineering OnLine, 5(1), 17. doi:10.1186/1475-925x-5-1

Comparison of enthalpy method and water fraction method to mathematically model water vaporization during RF ablation

[EN] During high-temperature energy-based therapies such as radiofrequency ablation (RFA) the target tissue reaches temperatures around 100ºC, which causes tissue dehydration by water vaporization. In order to be as realistic as possible, RFA theoretical models should include the formulation of these phenomena. There are currently two fixed mesh methods of modeling the electrical and thermal effects produced by water vaporization: the enthalpy method and the water fraction method. Our objective was to compare both methods, especially to assess the thermal and electrical performance in terms of electrical impedance progress during heating, distributions of temperature, and temperature progress at some specific locations. The results showed the performance of both methods to be qualitatively analogous, with similar impedance progress, temperature distributions and temperature progress. They were hence equally able to mimic the thermal and electrical performance in a pulsed protocol, i.e. during the period without applying RF power. The main difference between the methods was the time at which impedance started to rise. All these findings suggest that the two methods offer equivalent results in RFA modeling. However, since the enthalpy method has one less problem to be solved (dynamic volume fraction of liquid water in the tissue) it is less complex, has a lower computational cost and therefore seems to be more suitable for modeling RFA with dry or internally cooled electrodes, i.e. those in which there is no interstitial saline infusion. However, the water fraction method would be more appropriate in the case of RFA with externally irrigated electrodes.This work received financial support from the Spanish “Plan Nacional de I+D+I del Ministerio de Ciencia e Innovación” Grant No. TEC2011-27133-C02-01.Fatieieva, Y.; Almendárez, P.; Romero-Méndez, R.; Berjano, E.; Trujillo Guillen, M. (2014). Comparison of enthalpy method and water fraction method to mathematically model water vaporization during RF ablation. Journal of Advances in Biomedical Engineering and Technology. 1(1):8-14. https://doi.org/10.15379/2409-3394.2014.01.01.2S8141

Análisis radiográfico de los parámetros espinopélvicos obtenidos con el dispositivo de TLIF anterior. Estudio multicéntrico

Objetivo: Comunicar los resultados obtenidos según la posición del dispositivo de TLIF anterior. Materiales y Métodos: Estudio multicéntrico, observacional, analítico, transversal, de recuperación retrospectiva. Se evaluaron los parámetros espinopélvicos prey posoperatorios de espinogramas de 20 pacientes que fueron operados entre septiembre de 2019 y agosto de 2021. Se incluyó a pacientes sometidos a artrodesis lumbar con implante de tipo TLIF anterior. Se excluyó a pacientes sin espinograma pre- o posquirúrgico y más de un dispositivo. Resultados: La media de la lordosis monosegmentaria fue de 13,33° antes de la cirugía y de 18,81° después (p 0,001). Conclusiones: Los resultados de la colocación de este tipo de dispositivos y su relación con la lordosis segmentaria fueron alentadores, se comprendió la importancia de la disposición de estos en el extremo anterior del espacio discal. Nivel de Evidencia: I

RF tumor ablation with internally cooled electrodes and saline infusion: what is the optimal location of the saline infusion?

<p>Abstract</p> <p>Background</p> <p>Radiofrequency ablation (RFA) of tumors by means of internally cooled electrodes (ICE) combined with interstitial infusion of saline may improve clinical results. To date, infusion has been conducted through outlets placed on the surface of the cooled electrode. However, the effect of infusion at a distance from the electrode surface is unknown. Our aim was to assess the effect of perfusion distance (PD) on the coagulation geometry and deposited power during RFA using ICE.</p> <p>Methods</p> <p>Experiments were performed on excised bovine livers. Perfusion distance (PD) was defined as the shortest distance between the infusion outlet and the surface of the ICE. We considered three values of PD: 0, 2 and 4 mm. Two sets of experiments were considered: 1) 15 ablations of 10 minutes (n ≥ 4 for each PD), in order to evaluate the effect of PD on volume and diameters of coagulation; and 2) 20 additional ablations of 20 minutes. The effect of PD on deposited power and relative frequency of uncontrolled impedance rises (roll-off) was evaluated using the results from the two sets of experiments (n ≥ 7 for each PD). Comparisons between PD were performed by analysis of variance or Kruskal-Wallis test. Additionally, non-linear regression models were performed to elucidate the best PD in terms of coagulation volume and diameter, and the occurrence of uncontrolled impedance rises.</p> <p>Results</p> <p>The best-fit least square functions were always obtained with quadratic curves where volume and diameters of coagulation were maximum for a PD of 2 mm. A thirty per cent increase in volume coagulation was observed for this PD value compared to other values (<it>P </it>< 0.05). Likewise, the short coagulation diameter was nearly twenty five per cent larger for a 2 mm PD than for 0 mm. Regarding deposited power, the best-fit least square function was obtained by a quadratic curve with a 2 mm PD peak. This matched well with the higher relative frequency of uncontrolled impedance rises for PD of 0 and 4 mm.</p> <p>Conclusion</p> <p>Saline perfusion at around 2 mm from the electrode surface while using an ICE in RFA improves deposition of energy and enlarges coagulation volume.</p

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

Purpose: The Cool-tip electrode is one of the most widely employed applicators in radiofrequency (RF) hepatic ablation. Previous research demonstrated that it is possible to enlarge coagulation volume when the single cooled electrode is associated with distant infusion of saline (hybrid applicator). The aim of this study was to compare the electrical-thermal behaviour of the Cool-tip electrode with that of the hybrid applicator. Materials and methods: Forty-two RF ablations were performed on a total of 10 pigs: 22 with the Cool-tip electrode and 20 with the hybrid applicator (low infused saline volumetric flow rate of 6 mL/h at 2 mm distance). We compared both electrical performance (delivered power and number of roll-offs, i.e. sudden rises in impedance that interrupt the power delivery) and coagulation zone characteristics. In addition, we built a one-dimensional model to provide a basic physical explanation of the difference in performance between the different applicators. Results: The experimental results showed that the number of roll-offs with the Cool-tip electrode was higher (24.3 3.1 versus 6.7 7.0). The hybrid applicator created larger coagulation volumes (19.7 9.5 cm3 versus 9.5 5.8 cm3 ) with larger transverse diameters (2.5 0.6 versus 1.9 0.5 cm). The one-dimensional model confirmed the delay in the incidence of the first roll-off, but not the heterogeneity of the hybrid applicator’s electrical performance in the experiments. Conclusions: The hybrid applicator produces fewer roll-off episodes than the Cool-tip electrode and creates larger coagulation volumes with larger transverse diameters.This work received financial support from the Spanish Plan Nacional de I_D_i del Ministerio de Ciencia e Innovacion, grants TEC2008-01369/TEC and TEC2011-27133-C02-01. The authors thank CONACyT (Mexico) for support from project CB-2007/84618 that enabled research visits of R. Romero-Mendez to the Universidad Politecnica de Valencia (Spain) and E.J. Berjano to the Universidad Autonoma de San Luis Potosi (Mexico). The translation of this paper was funded by the Universitat Politecnica de Valencia, Spain. F. Burdio and E. Berjano declare an interest (stock ownership) in Apeiron Medical SL, a company which has a licence for the patent application US 2010/137856 A1, on which the hybrid applicator tested in this study is based. The other authors have no conflict of interests or financial ties to disclose. The authors alone are responsible for the content and writing of the paper.Romero-Méndez, R.; Tobajas, P.; Burdío Pinilla, F.; González, A.; Navarro Gonzalo, A.; Grande, L.; Berjano, E. (2012). Electrical-thermal performance of a cooled RF applicator for hepatic ablation with additional distant infusion of hypertonic saline: In vivo study and preliminary computer modeling. International Journal of Hyperthermia. 28(7):653-662. https://doi.org/10.3109/02656736.2012.711894S65366228

Small ablation zones created previous to saline infusion result in enlargement of the coagulated area during perfusion RF ablation: an ex vivo experimental study

[EN] One of the strategies for enlarging coagulation zone dimensions during RF ablation of liver tumours is to infuse saline solutions into the tissue during ablation. The aim of this study was to evaluate experimentally whether the creation of a small coagulation adjacent to a bipolar RF applicator and prior to perfused RF ablation would allow enlargement of the coagulation zone. Thirty bipolar RF ablations (group A, n = 15; group B, n = 15) were performed in excised bovine livers. Additionally, in group B a monopolar RF application (60 W, 20 s) was performed before bipolar ablation using three small additional electrodes. Electrical parameters and dimensions of the ablation zone were compared between groups. Despite the fact that all three ablation zone diameters were greater in group B, only one of the minor diameters was significantly longer (5.52 +/- 0.66 cm versus 4.87 +/- 0.47 cm). Likewise, volume was significantly bigger in group B(100.26 +/- 24.10 cm(3) versus 79.56 +/- 15.59 cm(3)). There were no differences in the impedance evolution, allowing a relatively high constant power in both groups (around 90 W). The efficacy of delivering energy (expressed as the delivered energy per coagulation volume) was significantly better in group B, showing a lower value (578 J cm(-3) versus 752 J cm(-3)). These results suggest that the creation of small ablation zones prior to saline infusion improves the performance of this perfusion system, and hence the total volume.The authors would like to thank the R+D+i Linguistic Assistance Office at the Universidad Politécnica of Valencia for their help in revising this paper. They also thank the reviewers for their constructive comments. This work was partially supported by the Programa de Promoción de la Investigación Biomédica y en Ciencias de la Salud del Ministerio de Sanidad y Consumo of Spain (PI052498) and by the Plan Nacional de Investigación Científica, Desarrollo e Innovación Tecnológica del Ministerio de Educación y Ciencia of Spain (TEC 2005-04199/TCM).Navarro, AC.; Burdío, F.; Berjano, E.; Güemes, A.; Burdío, JM.; Sousa, R.; Lozano, R.... (2007). Small ablation zones created previous to saline infusion result in enlargement of the coagulated area during perfusion RF ablation: an ex vivo experimental study. Physiological Measurement. 28(6):29-37. https://doi.org/10.1088/0967-3334/28/6/N02S2937286Aubé, C., Schmidt, D., Brieger, J., Schenk, M., Kroeber, S., Vielle, B., … Pereira, P. L. (2006). Influence of NaCl Concentrations on Coagulation, Temperature, and Electrical Conductivity Using a Perfusion Radiofrequency Ablation System: An Ex Vivo Experimental Study. 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