Could it be advantageous to tune the temperature controller during radiofrequency ablation? A feasibility study using theoretical models

Purpose: To assess whether tailoring the Kp and Ki values of a proportional-integral (PI) controller during radiofrequency (RF) cardiac ablation could be advantageous from the point of view of the dynamic behaviour of the controller, in particular, whether control action could be speeded up and larger lesions obtained. Methods: Theoretical models were built and solved by the finite element method. RF cardiac ablations were simulated with temperature controlled at 55 degrees C. Specific PI controllers were implemented with Kp and Ki parameters adapted to cases with different tissue values (specific heat, thermal conductivity and electrical conductivity) electrode-tissue contact characteristics (insertion depth, cooling effect of circulating blood) and electrode characteristics (size, location and arrangement of the temperature sensor in the electrode). Results: The lesion dimensions and T(max) remained almost unchanged when the specific PI controller was used instead of one tuned for the standard case: T(max) varied less than 1.9 degrees C, lesion width less than 0.2 mm, and lesion depth less than 0.3 mm. As expected, we did observe a direct logical relationship between the response time of each controller and the transient value of electrode temperature. Conclusion: The results suggest that a PI controller designed for a standard case (such as that described in this study), could offer benefits under different tissue conditions, electrode-tissue contact, and electrode characteristics.This work received financial support from the Spanish 'Plan Nacional de I+D+I del Ministerio de Ciencia e Innovacion' Grant no. TEC2008-01369/TEC and FEDER Project MTM2010-14909. The translation of this paper was funded by the Universitat Politecnica de Valencia, Spain. The authors alone are responsible for the content and writing of the paperAlba Martínez, J.; Trujillo Guillen, M.; Blasco Giménez, RM.; Berjano Zanón, E. (2011). Could it be advantageous to tune the temperature controller during radiofrequency ablation? A feasibility study using theoretical models. International Journal of Hyperthermia. 27(6):539-548. https://doi.org/10.3109/02656736.2011.586665S539548276Gaita, F., Caponi, D., Pianelli, M., Scaglione, M., Toso, E., Cesarani, F., … Leclercq, J. F. (2010). Radiofrequency Catheter Ablation of Atrial Fibrillation: A Cause of Silent Thromboembolism? Circulation, 122(17), 1667-1673. doi:10.1161/circulationaha.110.937953Anfinsen, O.-G., Aass, H., Kongsgaard, E., Foerster, A., Scott, H., & Amlie, J. P. (1999). Journal of Interventional Cardiac Electrophysiology, 3(4), 343-351. doi:10.1023/a:1009840004782PETERSEN, H. H., CHEN, X., PIETERSEN, A., SVENDSEN, J. H., & HAUNSO, S. (2000). Tissue Temperatures and Lesion Size During Irrigated Tip Catheter Radiofrequency Ablation: An In Vitro Comparison of Temperature-Controlled Irrigated Tip Ablation, Power-Controlled Irrigated Tip Ablation, and Standard Temperature-Controlled Ablation. Pacing and Clinical Electrophysiology, 23(1), 8-17. doi:10.1111/j.1540-8159.2000.tb00644.xTungjitkusolmun, S., Woo, E. J., Cao, H., Tsai, J. Z., Vorperian, V. R., & Webster, J. G. (2000). Thermal—electrical finite element modelling for radio frequency cardiac ablation: Effects of changes in myocardial properties. Medical & Biological Engineering & Computing, 38(5), 562-568. doi:10.1007/bf02345754Lai, Y.-C., Choy, Y. B., Haemmerich, D., Vorperian, V. R., & Webster, J. G. (2004). Lesion Size Estimator of Cardiac Radiofrequency Ablation at Different Common Locations With Different Tip Temperatures. IEEE Transactions on Biomedical Engineering, 51(10), 1859-1864. doi:10.1109/tbme.2004.831529Jain, M. K., & Wolf, P. D. (1999). Temperature-controlled and constant-power radio-frequency ablation: what affects lesion growth? IEEE Transactions on Biomedical Engineering, 46(12), 1405-1412. doi:10.1109/10.804568Panescu, D., Whayne, J. G., Fleischman, S. D., Mirotznik, M. S., Swanson, D. K., & Webster, J. G. (1995). Three-dimensional finite element analysis of current density and temperature distributions during radio-frequency ablation. IEEE Transactions on Biomedical Engineering, 42(9), 879-890. doi:10.1109/10.412649Hong Cao, Vorperian, V. R., Tungjitkusolmun, S., Jan-Zern Tsai, Haemmerich, D., Young Bin Choy, & Webster, J. G. (2001). Flow effect on lesion formation in RF cardiac catheter ablation. IEEE Transactions on Biomedical Engineering, 48(4), 425-433. doi:10.1109/10.915708Tungjitkusolmun, S., Vorperian, V. R., Bhavaraju, N., Cao, H., Tsai, J.-Z., & Webster, J. G. (2001). Guidelines for predicting lesion size at common endocardial locations during radio-frequency ablation. IEEE Transactions on Biomedical Engineering, 48(2), 194-201. doi:10.1109/10.909640Schutt, D., Berjano, E. J., & Haemmerich, D. (2009). Effect of electrode thermal conductivity in cardiac radiofrequency catheter ablation: A computational modeling study. International Journal of Hyperthermia, 25(2), 99-107. doi:10.1080/02656730802563051Langberg, J. J., Calkins, H., el-Atassi, R., Borganelli, M., Leon, A., Kalbfleisch, S. J., & Morady, F. (1992). Temperature monitoring during radiofrequency catheter ablation of accessory pathways. Circulation, 86(5), 1469-1474. doi:10.1161/01.cir.86.5.1469Calkins, H., Prystowsky, E., Carlson, M., Klein, L. S., Saul, J. P., & Gillette, P. (1994). Temperature monitoring during radiofrequency catheter ablation procedures using closed loop control. Atakr Multicenter Investigators Group. Circulation, 90(3), 1279-1286. doi:10.1161/01.cir.90.3.1279Lennox CD, Temperature controlled RF coagulation. Patent number: 5.122.137 Hudson NHEdwards SD, Stern RA, Electrode and associated system using thermally insulated temperature sensing elements. Patent number: US Patent 5,456,682Panescu D, Fleischman SD, Whayne JG, Swanson DK, (EP Technology. Effects of temperature sensor placement on performance of temperature-controlled ablation. IEEE 17th Annual Conference, Engineering in Medicine and Biology Society, Montreal, Canada (1995)BLOUIN, L. T., MARCUS, F. I., & LAMPE, L. (1991). Assessment of Effects of a Radiofrequency Energy Field and Thermistor Location in an Electrode Catheter on the Accuracy of Temperature Measurement. Pacing and Clinical Electrophysiology, 14(5), 807-813. doi:10.1111/j.1540-8159.1991.tb04111.xBerjano, E. J. (2006). BioMedical Engineering OnLine, 5(1), 24. doi:10.1186/1475-925x-5-24Bhavaraju, N. C., Cao, H., Yuan, D. Y., Valvano, J. W., & Webster, J. G. (2001). Measurement of directional thermal properties of biomaterials. IEEE Transactions on Biomedical Engineering, 48(2), 261-267. doi:10.1109/10.909647Hong Cao, Tungjitkusolmun, S., Young Bin Choy, Jang-Zern Tsai, Vorperian, V. R., & Webster, J. G. (2002). Using electrical impedance to predict catheter-endocardial contact during RF cardiac ablation. IEEE Transactions on Biomedical Engineering, 49(3), 247-253. doi:10.1109/10.983459PETERSEN, 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.xLANGBERG, J. J., LEE, M. A., CHIN, M. C., & ROSENQVIST, M. (1990). Radiofrequency Catheter Ablation: The Effect of Electrode Size on Lesion Volume In Vivo. Pacing and Clinical Electrophysiology, 13(10), 1242-1248. doi:10.1111/j.1540-8159.1990.tb02022.

A computational model for real-time calculation of electric field due to transcranial magnetic stimulation in clinics

The aim of this paper is to propose an approach for an accurate and fast (real-time) computation of the electric field induced inside the whole brain volume during a transcranial magnetic stimulation (TMS) procedure. The numerical solution implements the admittance method for a discretized realistic brain model derived from Magnetic Resonance Imaging (MRI). Results are in a good agreement with those obtained using commercial codes and require much less computational time. An integration of the developed codewith neuronavigation toolswill permit real-time evaluation of the stimulated brain regions during the TMSdelivery, thus improving the efficacy of clinical applications

Image Enhancement and Noise Reduction Using Modified Delay-Multiply-and-Sum Beamformer: Application to Medical Photoacoustic Imaging

Photoacoustic imaging (PAI) is an emerging biomedical imaging modality capable of providing both high contrast and high resolution of optical and UltraSound (US) imaging. When a short duration laser pulse illuminates the tissue as a target of imaging, tissue induces US waves and detected waves can be used to reconstruct optical absorption distribution. Since receiving part of PA consists of US waves, a large number of beamforming algorithms in US imaging can be applied on PA imaging. Delay-and-Sum (DAS) is the most common beamforming algorithm in US imaging. However, make use of DAS beamformer leads to low resolution images and large scale of off-axis signals contribution. To address these problems a new paradigm namely Delay-Multiply-and-Sum (DMAS), which was used as a reconstruction algorithm in confocal microwave imaging for breast cancer detection, was introduced for US imaging. Consequently, DMAS was used in PA imaging systems and it was shown this algorithm results in resolution enhancement and sidelobe degrading. However, in presence of high level of noise the reconstructed image still suffers from high contribution of noise. In this paper, a modified version of DMAS beamforming algorithm is proposed based on DAS inside DMAS formula expansion. The quantitative and qualitative results show that proposed method results in more noise reduction and resolution enhancement in expense of contrast degrading. For the simulation, two-point target, along with lateral variation in two depths of imaging are employed and it is evaluated under high level of noise in imaging medium. Proposed algorithm in compare to DMAS, results in reduction of lateral valley for about 19 dB followed by more distinguished two-point target. Moreover, levels of sidelobe are reduced for about 25 dB.Comment: This paper was accepted and presented at Iranian Conference on Electrical Engineering (ICEE) 201

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