Automatic control of finite element models for temperature-controlled radiofrequency ablation

BACKGROUND: The finite element method (FEM) has been used to simulate cardiac and hepatic radiofrequency (RF) ablation. The FEM allows modeling of complex geometries that cannot be solved by analytical methods or finite difference models. In both hepatic and cardiac RF ablation a common control mode is temperature-controlled mode. Commercial FEM packages don't support automating temperature control. Most researchers manually control the applied power by trial and error to keep the tip temperature of the electrodes constant. METHODS: We implemented a PI controller in a control program written in C++. The program checks the tip temperature after each step and controls the applied voltage to keep temperature constant. We created a closed loop system consisting of a FEM model and the software controlling the applied voltage. The control parameters for the controller were optimized using a closed loop system simulation. RESULTS: We present results of a temperature controlled 3-D FEM model of a RITA model 30 electrode. The control software effectively controlled applied voltage in the FEM model to obtain, and keep electrodes at target temperature of 100°C. The closed loop system simulation output closely correlated with the FEM model, and allowed us to optimize control parameters. DISCUSSION: The closed loop control of the FEM model allowed us to implement temperature controlled RF ablation with minimal user input

Computer modeling of an impedance-controlled pulsing protocol for RF tumor ablation with a cooled electrode

[EN] 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, 3cm 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 degrees 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.This work was supported by the Spanish Plan Estatal de Investigacion, Desarrollo e Innovacion Orientada a los Retos de la Sociedad under grant number TEC2014-52383-C3-R (TEC2014-52383-C3-1-R). The authors alone are responsible for the content and writing of the paper.Trujillo Guillen, M.; Bon Corbín, J.; Rivera Ortun, MJ.; Burdio, F.; Berjano, E. (2016). Computer modeling of an impedance-controlled pulsing protocol for RF tumor ablation with a cooled electrode. International Journal of Hyperthermia. 32(8):931-939. doi:10.1080/02656736.2016.1190868S931939328Hocquelet, A., Balageas, P., Laurent, C., Blanc, J.-F., Frulio, N., Salut, C., … Trillaud, H. (2015). Radiofrequency ablation versus surgical resection for hepatocellular carcinoma within the Milan criteria: A study of 281 Western patients. International Journal of Hyperthermia, 31(7), 749-757. doi:10.3109/02656736.2015.1068382Fukushima, T., Ikeda, K., Kawamura, Y., Sorin, Y., Hosaka, T., Kobayashi, M., … Kumada, H. (2015). Randomized Controlled Trial Comparing the Efficacy of Impedance Control and Temperature Control of Radiofrequency Interstitial Thermal Ablation for Treating Small Hepatocellular Carcinoma. Oncology, 89(1), 47-52. doi:10.1159/000375166Goldberg, S. N., Stein, M. C., Gazelle, G. S., Sheiman, R. G., Kruskal, J. B., & Clouse, M. E. (1999). Percutaneous Radiofrequency Tissue Ablation: Optimization of Pulsed-Radiofrequency Technique to Increase Coagulation Necrosis. Journal of Vascular and Interventional Radiology, 10(7), 907-916. doi:10.1016/s1051-0443(99)70136-3Ahmed, M., Liu, Z., Humphries, S., & Nahum Goldberg, S. (2008). Computer modeling of the combined effects of perfusion, electrical conductivity, and thermal conductivity on tissue heating patterns in radiofrequency tumor ablation. International Journal of Hyperthermia, 24(7), 577-588. doi:10.1080/02656730802192661Lobo, S. M., Liu, Z.-J., Yu, N. C., Humphries, S., Ahmed, M., Cosman, E. R., … Goldberg, S. N. (2005). RF tumour ablation: Computer simulation and mathematical modelling of the effects of electrical and thermal conductivity. International Journal of Hyperthermia, 21(3), 199-213. doi:10.1080/02656730400001108Solazzo, S. A., Liu, Z., Lobo, S. M., Ahmed, M., Hines-Peralta, A. U., Lenkinski, R. E., & Goldberg, S. N. (2005). Radiofrequency Ablation: Importance of Background Tissue Electrical Conductivity—An Agar Phantom and Computer Modeling Study. Radiology, 236(2), 495-502. doi:10.1148/radiol.2362040965Barauskas, R., Gulbinas, A., & Barauskas, G. (2007). Investigation of radiofrequency ablation process in liver tissue by finite element modeling and experiment. Medicina, 43(4), 310. doi:10.3390/medicina43040039Haemmerich, D., & Wood, B. J. (2006). Hepatic radiofrequency ablation at low frequencies preferentially heats tumour tissue. International Journal of Hyperthermia, 22(7), 563-574. doi:10.1080/02656730601024727Haemmerich, 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.2003.809488Schutt, D. J., & Haemmerich, D. (2008). Effects of variation in perfusion rates and of perfusion models in computational models of radio frequency tumor ablation. Medical Physics, 35(8), 3462-3470. doi:10.1118/1.2948388Zhang, B., Moser, M. A. J., Zhang, E. M., Luo, Y., & Zhang, W. (2015). Numerical analysis of the relationship between the area of target tissue necrosis and the size of target tissue in liver tumours with pulsed radiofrequency ablation. International Journal of Hyperthermia, 31(7), 715-725. doi:10.3109/02656736.2015.1058429Solazzo, S. A., Ahmed, M., Liu, Z., Hines-Peralta, A. U., & Goldberg, S. N. (2007). High-Power Generator for Radiofrequency Ablation: Larger Electrodes and Pulsing Algorithms in Bovine ex Vivo and Porcine in Vivo Settings. Radiology, 242(3), 743-750. doi:10.1148/radiol.2423052039Abraham, J. P., & Sparrow, E. M. (2007). A thermal-ablation bioheat model including liquid-to-vapor phase change, pressure- and necrosis-dependent perfusion, and moisture-dependent properties. International Journal of Heat and Mass Transfer, 50(13-14), 2537-2544. doi:10.1016/j.ijheatmasstransfer.2006.11.045Pätz, T., Kröger, T., & Preusser, T. (2009). Simulation of Radiofrequency Ablation Including Water Evaporation. World Congress on Medical Physics and Biomedical Engineering, September 7 - 12, 2009, Munich, Germany, 1287-1290. doi:10.1007/978-3-642-03882-2_341Trujillo, M., Alba, J., & Berjano, E. (2012). Relationship between roll-off occurrence and spatial distribution of dehydrated tissue during RF ablation with cooled electrodes. International Journal of Hyperthermia, 28(1), 62-68. doi:10.3109/02656736.2011.631076Hall, S. K., Ooi, E. H., & Payne, S. J. (2015). Cell death, perfusion and electrical parameters are critical in models of hepatic radiofrequency ablation. International Journal of Hyperthermia, 31(5), 538-550. doi:10.3109/02656736.2015.1032370Chang, S.-J., Yu, W.-J., Chang, C.-C., & Chen, Y.-H. (2010). 7 PROTEOMICS ANALYSIS OF MALE REPRODUCTIVE PHYSIOLOGY BY TOONA SINENSIS ROEM. Reproductive BioMedicine Online, 20, S3-S4. doi:10.1016/s1472-6483(10)62425-xBeop-Min Kim, Jacques, S. L., Rastegar, S., Thomsen, S., & Motamedi, M. (1996). Nonlinear finite-element analysis of the role of dynamic changes in blood perfusion and optical properties in laser coagulation of tissue. IEEE Journal of Selected Topics in Quantum Electronics, 2(4), 922-933. doi:10.1109/2944.577317Doss, J. D. (1982). Calculation of electric fields in conductive media. Medical Physics, 9(4), 566-573. doi:10.1118/1.595107Jo, B., & Aksan, A. (2010). Prediction of the extent of thermal damage in the cornea during conductive keratoplasty. Journal of Thermal Biology, 35(4), 167-174. doi:10.1016/j.jtherbio.2010.02.004Belous, A., & Podhajsky, R. J. (2009). The effect of initial and dynamic liver conditions on RF ablation size: a study in perfused and non-perfused animal models. Energy-based Treatment of Tissue and Assessment V. doi:10.1117/12.809597Song, K. D., Lee, M. W., Park, H. J., Cha, D. I., Kang, T. W., Lee, J., … Rhim, H. (2015). Hepatic radiofrequency ablation:in vivoandex vivocomparisons of 15-gauge (G) and 17-G internally cooled electrodes. The British Journal of Radiology, 88(1050), 20140497. doi:10.1259/bjr.20140497Cha, J., Choi, D., Lee, M. W., Rhim, H., Kim, Y., Lim, H. K., … Park, C. K. (2009). Radiofrequency Ablation Zones in Ex Vivo Bovine and In Vivo Porcine Livers: Comparison of the Use of Internally Cooled Electrodes and Internally Cooled Wet Electrodes. CardioVascular and Interventional Radiology, 32(6), 1235-1240. doi:10.1007/s00270-009-9600-0Lee, J. M., Han, J. K., Chang, J. M., Chung, S. Y., Kim, S. H., Lee, J. Y., … Choi, B. I. (2006). Radiofrequency Ablation of the Porcine Liver In Vivo: Increased Coagulation with an Internally Cooled Perfusion Electrode. Academic Radiology, 13(3), 343-352. doi:10.1016/j.acra.2005.10.020Romero-Méndez, R., Tobajas, P., Burdío, F., Gonzalez, A., Navarro, 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 vivostudy and preliminary computer modeling. International Journal of Hyperthermia, 28(7), 653-662. doi:10.3109/02656736.2012.711894Ahmed, M., Lobo, S. M., Weinstein, J., Kruskal, J. B., Gazelle, G. S., Halpern, E. F., … Goldberg, S. N. (2002). Improved Coagulation with Saline Solution Pretreatment during Radiofrequency Tumor Ablation in a Canine Model. Journal of Vascular and Interventional Radiology, 13(7), 717-724. doi:10.1016/s1051-0443(07)61850-8Chinn, S. B., Lee, F. T., Kennedy, G. D., Chinn, C., Johnson, C. D., Winter, T. C., … Mahvi, D. M. (2001). Effect of Vascular Occlusion on Radiofrequency Ablation of the Liver. American Journal of Roentgenology, 176(3), 789-795. doi:10.2214/ajr.176.3.1760789Arenas, J., Perez, J. J., Trujillo, M., & Berjano, E. (2014). Computer modeling and ex vivo experiments with a (saline-linked) irrigated electrode for RF-assisted heating. BioMedical Engineering OnLine, 13(1), 164. doi:10.1186/1475-925x-13-164González-Suárez, A., Trujillo, M., Burdío, F., Andaluz, A., & Berjano, E. (2012). Feasibility study of an internally cooled bipolar applicator for RF coagulation of hepatic tissue: Experimental and computational study. International Journal of Hyperthermia, 28(7), 663-673. doi:10.3109/02656736.2012.716900Schramm, W., Yang, D., Wood, B. J., Rattay, F., & Haemmerich, D. (2007). Contribution of Direct Heating, Thermal Conduction and Perfusion During Radiofrequency and Microwave Ablation. The Open Biomedical Engineering Journal, 1(1), 47-52. doi:10.2174/1874120700701010047Chang, I. A., & Nguyen, U. D. (2004). BioMedical Engineering OnLine, 3(1), 27. doi:10.1186/1475-925x-3-27Montgomery, R. S., Rahal, A., Dodd, G. D., Leyendecker, J. R., & Hubbard, L. G. (2004). Radiofrequency Ablation of Hepatic Tumors: Variability of Lesion Size Using a Single Ablation Device. American Journal of Roentgenology, 182(3), 657-661. doi:10.2214/ajr.182.3.1820657SCHUMACHER, B., EICK, O., WITTKAMPF, F., PEZOLD, C., TEBBENJOHANNS, J., JUNG, W., & LUDERITZ, B. (1999). Temperature Response Following Nontraumatic Low Power Radiofrequency Application. Pacing and Clinical Electrophysiology, 22(2), 339-343. doi:10.1111/j.1540-8159.1999.tb00448.xPETERSEN, H. H., & SVENDSEN, J. H. (2003). Can Lesion Size During Radiofrequency Ablation Be Predicted By the Temperature Rise to a Low Power Test Pulse in Vitro? Pacing and Clinical Electrophysiology, 26(8), 1653-1659. doi:10.1046/j.1460-9592.2003.t01-1-00248.

Hyperthermia and smart drug delivery systems for solid tumor therapy

Chemotherapy is a cornerstone of cancer therapy. Irrespective of the administered drug, it is crucial that adequate drug amounts reach all cancer cells. To achieve this, drugs first need to be absorbed, then enter the blood circulation, diffuse into the tumor interstitial space and finally reach the tumor cells. Next to chemoresistance, one of the most important factors for effective chemotherapy is adequate tumor drug uptake and penetration. Unfortunately, most chemotherapeutic agents do not have favorable properties. These compounds are cleared rapidly, distribute throughout all tissues in the body, with only low tumor drug uptake that is heterogeneously distributed within the tumor. Moreover, the typical microenvironment of solid cancers provides additional hurdles for drug delivery, such as heterogeneous vascular density and perfusion, high interstitial fluid pressure, and abundant stroma. The hope was that nanotechnology will solve most, if not all, of these drug delivery barriers. However, in spite of advances and decades of nanoparticle development, results are unsatisfactory. One promising recent development are nanoparticles which can be steered, and release content triggered by internal or external signals. Here we discuss these so-called smart drug delivery systems in cancer therapy with emphasis on mild hyperthermia as a trigger signal for drug delivery

An Electrode Array for Limiting Blood Loss During Liver Resection: Optimization via Mathematical Modeling

Liver resection is the current standard treatment for patients with both primary and metastatic liver cancer. The principal causes of morbidity and mortality after liver resection are related to blood loss (typically between 0.5 and 1 L), especially in cases where transfusion is required. Blood transfusions have been correlated with decreased long-term survival, increased risk of perioperative mortality and complications. The goal of this study was to evaluate different designs of a radiofrequency (RF) electrode array for use during liver resection. The purpose of this electrode array is to coagulate a slice of tissue including large vessels before resecting along that plane, thereby significantly reducing blood loss. Finite Element Method models were created to evaluate monopolar and bipolar power application, needle and blade shaped electrodes, as well as different electrode distances. Electric current density, temperature distribution, and coagulation zone sizes were measured. The best performance was achieved with a design of blade shaped electrodes (5 × 0.1 mm cross section) spaced 1.5 cm apart. The electrodes have power applied in bipolar mode to two adjacent electrodes, then switched sequentially in short intervals between electrode pairs to rapidly heat the tissue slice. This device produces a ~1.5 cm wide coagulation zone, with temperatures over 97 ºC throughout the tissue slice within 3 min, and may facilitate coagulation of large vessels

Contribution of Direct Heating, Thermal Conduction and Perfusion During Radiofrequency and Microwave Ablation

Both radiofrequency (RF) and microwave (MW) ablation devices are clinically used for tumor ablation. Several studies report less dependence on vascular mediated cooling of MW compared to RF ablation. We created computer models of a cooled RF needle electrode, and a dipole MW antenna to determine differences in tissue heat transfer

Multiwavelength study of extreme variability in LEDA 1154204: A changing-look event in a type 1.9 Seyfert

Context. Multiwavelength studies of transients in actively accreting supermassive black holes have revealed that large-amplitude variability is frequently linked to significant changes in the optical spectra -- a phenomenon referred to as changing-look AGN (CLAGN). Aim. In 2020, the Zwicky Transient Facility detected a transient flaring event in the type-1.9 AGN 6dFGS~gJ042838.8-000040, wherein a sharp increase in magnitude of $\sim$0.55 and $\sim$0.3 in the $g$- and $r$-bands, respectively, occurred over $\sim$40 days. Spectrum Roentgen Gamma (SRG)/eROSITA also observed the object in X-rays as part of its all-sky survey, but only after the flare had started decaying. Methods. We performed a three-year, multiwavelength follow-up campaign of the source to track its spectral and temporal characteristics. This campaign included multiple ground-based facilities for optical spectroscopic monitoring and space-based observatories including \textit{XMM-Newton} and \textit{Swift} for X-ray and UV observations. Results. An optical spectrum taken immediately after the peak revealed a changing-look event wherein the source had transitioned from type 1.9 to 1, with the appearance of a double-peaked broad H$\beta$ line and a blue continuum, both absent in an archival spectrum from 2005. The X-ray emission exhibits dramatic flux variation: a factor of $\sim$17, but with no spectral evolution, as the power-law photon index remained $\sim$1.9. There is no evidence of a soft X-ray excess. Overall the object exhibits no apparent signatures of a tidal disruption event. Conclusions. The transient event was likely triggered by a disk instability in a pre-existing accretion flow, culminating in the observed multi-wavelength variability and CLAGN event.Comment: 34 pages, 24 figures, Submitted to Astronomy & Astrophysic

Two-dimensional nanosecond electric field mapping based on cell electropermeabilization

Nanosecond, megavolt-per-meter electric pulses cause permeabilization of cells to small molecules, programmed cell death (apoptosis) in tumor cells, and are under evaluation as a treatment for skin cancer. We use nanoelectroporation and fluorescence imaging to construct two-dimensional maps of the electric field associated with delivery of 15 ns, 10 kV pulses to monolayers of the human prostate cancer cell line PC3 from three different electrode configurations: single-needle, five-needle, and flat-cut coaxial cable. Influx of the normally impermeant fluorescent dye YO-PRO-1 serves as a sensitive indicator of membrane permeabilization. The level of fluorescence emission after pulse exposure is proportional to the applied electric field strength. Spatial electric field distributions were compared in a plane normal to the center axis and 15-20 μm from the tip of the center electrode. Measurement results agree well with models for the three electrode arrangements evaluated in this study. This live-cell method for measuring a nanosecond pulsed electric field distribution provides an operationally meaningful calibration of electrode designs for biological applications and permits visualization of the relative sensitivities of different cell types to nanoelectropulse stimulation. PACS Codes: 87.85.M

Finite Element Analysis of Hepatic Radiofrequency Ablation Probes using Temperature-Dependent Electrical Conductivity

BACKGROUND: Few finite element models (FEM) have been developed to describe the electric field, specific absorption rate (SAR), and the temperature distribution surrounding hepatic radiofrequency ablation probes. To date, a coupled finite element model that accounts for the temperature-dependent electrical conductivity changes has not been developed for ablation type devices. While it is widely acknowledged that accounting for temperature dependent phenomena may affect the outcome of these models, the effect has not been assessed. METHODS: The results of four finite element models are compared: constant electrical conductivity without tissue perfusion, temperature-dependent conductivity without tissue perfusion, constant electrical conductivity with tissue perfusion, and temperature-dependent conductivity with tissue perfusion. RESULTS: The data demonstrate that significant errors are generated when constant electrical conductivity is assumed in coupled electrical-heat transfer problems that operate at high temperatures. These errors appear to be closely related to the temperature at which the ablation device operates and not to the amount of power applied by the device or the state of tissue perfusion. CONCLUSION: Accounting for temperature-dependent phenomena may be critically important in the safe operation of radiofrequency ablation device that operate near 100°C

Thermal modeling of lesion growth with radiofrequency ablation devices

BACKGROUND: Temperature is a frequently used parameter to describe the predicted size of lesions computed by computational models. In many cases, however, temperature correlates poorly with lesion size. Although many studies have been conducted to characterize the relationship between time-temperature exposure of tissue heating to cell damage, to date these relationships have not been employed in a finite element model. METHODS: We present an axisymmetric two-dimensional finite element model that calculates cell damage in tissues and compare lesion sizes using common tissue damage and iso-temperature contour definitions. The model accounts for both temperature-dependent changes in the electrical conductivity of tissue as well as tissue damage-dependent changes in local tissue perfusion. The data is validated using excised porcine liver tissues. RESULTS: The data demonstrate the size of thermal lesions is grossly overestimated when calculated using traditional temperature isocontours of 42°C and 47°C. The computational model results predicted lesion dimensions that were within 5% of the experimental measurements. CONCLUSION: When modeling radiofrequency ablation problems, temperature isotherms may not be representative of actual tissue damage patterns