2,708 research outputs found

    Respiratory organ motion in interventional MRI : tracking, guiding and modeling

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    Respiratory organ motion is one of the major challenges in interventional MRI, particularly in interventions with therapeutic ultrasound in the abdominal region. High-intensity focused ultrasound found an application in interventional MRI for noninvasive treatments of different abnormalities. In order to guide surgical and treatment interventions, organ motion imaging and modeling is commonly required before a treatment start. Accurate tracking of organ motion during various interventional MRI procedures is prerequisite for a successful outcome and safe therapy. In this thesis, an attempt has been made to develop approaches using focused ultrasound which could be used in future clinically for the treatment of abdominal organs, such as the liver and the kidney. Two distinct methods have been presented with its ex vivo and in vivo treatment results. In the first method, an MR-based pencil-beam navigator has been used to track organ motion and provide the motion information for acoustic focal point steering, while in the second approach a hybrid imaging using both ultrasound and magnetic resonance imaging was combined for advanced guiding capabilities. Organ motion modeling and four-dimensional imaging of organ motion is increasingly required before the surgical interventions. However, due to the current safety limitations and hardware restrictions, the MR acquisition of a time-resolved sequence of volumetric images is not possible with high temporal and spatial resolution. A novel multislice acquisition scheme that is based on a two-dimensional navigator, instead of a commonly used pencil-beam navigator, was devised to acquire the data slices and the corresponding navigator simultaneously using a CAIPIRINHA parallel imaging method. The acquisition duration for four-dimensional dataset sampling is reduced compared to the existing approaches, while the image contrast and quality are improved as well. Tracking respiratory organ motion is required in interventional procedures and during MR imaging of moving organs. An MR-based navigator is commonly used, however, it is usually associated with image artifacts, such as signal voids. Spectrally selective navigators can come in handy in cases where the imaging organ is surrounding with an adipose tissue, because it can provide an indirect measure of organ motion. A novel spectrally selective navigator based on a crossed-pair navigator has been developed. Experiments show the advantages of the application of this novel navigator for the volumetric imaging of the liver in vivo, where this navigator was used to gate the gradient-recalled echo sequence

    Thermal ablation of biological tissues in disease treatment: A review of computational models and future directions

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    Percutaneous thermal ablation has proved to be an effective modality for treating both benign and malignant tumors in various tissues. Among these modalities, radiofrequency ablation (RFA) is the most promising and widely adopted approach that has been extensively studied in the past decades. Microwave ablation (MWA) is a newly emerging modality that is gaining rapid momentum due to its capability of inducing rapid heating and attaining larger ablation volumes, and its lesser susceptibility to the heat sink effects as compared to RFA. Although the goal of both these therapies is to attain cell death in the target tissue by virtue of heating above 50 oC, their underlying mechanism of action and principles greatly differs. Computational modelling is a powerful tool for studying the effect of electromagnetic interactions within the biological tissues and predicting the treatment outcomes during thermal ablative therapies. Such a priori estimation can assist the clinical practitioners during treatment planning with the goal of attaining successful tumor destruction and preservation of the surrounding healthy tissue and critical structures. This review provides current state-of- the-art developments and associated challenges in the computational modelling of thermal ablative techniques, viz., RFA and MWA, as well as touch upon several promising avenues in the modelling of laser ablation, nanoparticles assisted magnetic hyperthermia and non- invasive RFA. The application of RFA in pain relief has been extensively reviewed from modelling point of view. Additionally, future directions have also been provided to improve these models for their successful translation and integration into the hospital work flow

    Monitoring thermal ablation via microwave tomography. An ex vivo experimental assessment

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    Thermal ablation treatments are gaining a lot of attention in the clinics thanks to their reduced invasiveness and their capability of treating non-surgical patients. The effectiveness of these treatments and their impact in the hospital's routine would significantly increase if paired with a monitoring technique able to control the evolution of the treated area in real-time. This is particularly relevant in microwave thermal ablation, wherein the capability of treating larger tumors in a shorter time needs proper monitoring. Current diagnostic imaging techniques do not provide effective solutions to this issue for a number of reasons, including economical sustainability and safety. Hence, the development of alternative modalities is of interest. Microwave tomography, which aims at imaging the electromagnetic properties of a target under test, has been recently proposed for this scope, given the significant temperature-dependent changes of the dielectric properties of human tissues induced by thermal ablation. In this paper, the outcomes of the first ex vivo experimental study, performed to assess the expected potentialities of microwave tomography, are presented. The paper describes the validation study dealing with the imaging of the changes occurring in thermal ablation treatments. The experimental test was carried out on two ex vivo bovine liver samples and the reported results show the capability of microwave tomography of imaging the transition between ablated and untreated tissue. Moreover, the discussion section provides some guidelines to follow in order to improve the achievable performances

    Review of the mathematical functions used to model the temperature dependence of electrical and thermal conductivities of biological tissue in radiofrequency ablation

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    Purpose: Although theoretical modelling is widely used to study different aspects of radiofrequency ablation (RFA), its utility is directly related to its realism. An important factor in this realism is the use of mathematical functions to model the temperature dependence of thermal (k) and electrical (sigma) conductivities of tissue. Our aim was to review the piecewise mathematical functions most commonly used for modelling the temperature dependence of k and sigma in RFA computational modelling. Materials and methods: We built a hepatic RFA theoretical model of a cooled electrode and compared lesion dimensions and impedance evolution with combinations of mathematical functions proposed in previous studies. We employed the thermal damage contour D63 to compute the lesion dimension contour, which corresponds to Omega = 1, Omega being local thermal damage assessed by the Arrhenius damage model. Results: The results were very similar in all cases in terms of impedance evolution and lesion size after 6 min of ablation. Although the relative differences between cases in terms of time to first roll-off (abrupt increase in impedance) were as much as 12%, the maximum relative differences in terms of the short lesion (transverse) diameter were below 3.5%. Conclusions: The findings suggest that the different methods of modelling temperature dependence of k and sigma reported in the literature do not significantly affect the computed lesion diameter.This work received financial support from the Spanish Plan Nacional de I þ D þ I del Ministerio de Ciencia e Innovacio´n, grant no. TEC2011-27133-C02-01, and from the PAID-06-11 UPV, grant ref. 1988. The authors alone are responsible for the content and writing of the paper.Trujillo Guillen, M.; Berjano, E. (2013). Review of the mathematical functions used to model the temperature dependence of electrical and thermal conductivities of biological tissue in radiofrequency ablation. International Journal of Hyperthermia. 29(6):590-597. https://doi.org/10.3109/02656736.2013.807438S590597296Radiofrequency ablation in liver tumours. (2004). Annals of Oncology, 15(suppl_4), iv313-iv317. doi:10.1093/annonc/mdh945McAchran, S. E., Lesani, O. A., & Resnick, M. I. (2005). Radiofrequency ablation of renal tumors: Past, present, and future. Urology, 66(5), 15-22. doi:10.1016/j.urology.2005.06.127Di Staso, M., Zugaro, L., Gravina, G. L., Bonfili, P., Marampon, F., Di Nicola, L., … Tombolini, V. (2011). A feasibility study of percutaneous radiofrequency ablation followed by radiotherapy in the management of painful osteolytic bone metastases. European Radiology, 21(9), 2004-2010. doi:10.1007/s00330-011-2133-3Sharma, R., Wagner, J. L., & Hwang, R. F. (2011). Ablative Therapies of the Breast. 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A Theoretical and Experimental Analysis of Radiofrequency Ablation with a Multielectrode, Phased, Duty-Cycled System. Pacing and Clinical Electrophysiology, 33(9), 1089-1100. doi:10.1111/j.1540-8159.2010.02801.xBerjano, E. J., Alió, J. L., & Saiz, J. (2005). Modeling for radio-frequency conductive keratoplasty: implications for the maximum temperature reached in the cornea. Physiological Measurement, 26(3), 157-172. doi:10.1088/0967-3334/26/3/002Pätz, 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_341Jain, M. K., & Wolf, P. D. (2000). A Three-Dimensional Finite Element Model of Radiofrequency Ablation with Blood Flow and its Experimental Validation. Annals of Biomedical Engineering, 28(9), 1075-1084. doi:10.1114/1.1310219Chang, I. A., & Nguyen, U. D. (2004). 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Analysis of Tissue and Arterial Blood Temperatures in the Resting Human Forearm. Journal of Applied Physiology, 85(1), 5-34. doi:10.1152/jappl.1998.85.1.5Pearce, J., Panescu, D., & Thomsen, S. (2005). Simulation of diopter changes in radio frequency conductive keratoplasty in the cornea. Modelling in Medicine and Biology VI. doi:10.2495/bio050451Zhao, G., Zhang, H.-F., Guo, X.-J., Luo, D.-W., & Gao, D.-Y. (2007). Effect of blood flow and metabolism on multidimensional heat transfer during cryosurgery. Medical Engineering & Physics, 29(2), 205-215. doi:10.1016/j.medengphy.2006.03.005Berjano, E. J., Burdío, F., Navarro, A. C., Burdío, J. M., Güemes, A., Aldana, O., … Gregorio, M. A. de. (2006). Improved perfusion system for bipolar radiofrequency ablation of liver: preliminary findings from a computer modeling study. Physiological Measurement, 27(10), N55-N66. doi:10.1088/0967-3334/27/10/n03Trujillo, 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:10.3109/02656736.2011.631076Doss, J. D. (1982). Calculation of electric fields in conductive media. Medical Physics, 9(4), 566-573. doi:10.1118/1.595107Chang, 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:10.1109/2944.577317Berjano, E. J., Saiz, J., & Ferrero, J. M. (2002). 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    LARGE TARGET TISSUE NECROSIS OF RADIOFREQUENCY ABLATION USING MATHEMATICAL MODELLING

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    Radiofrequency ablation (RFA) is a clinic tool for the treatment of various target tissues. However, one of the major limitations with RFA is the ‘small’ size of target tissues that can be effectively ablated. By small it is meant the size of the target tissue is less than 3 cm in diameter of the tissue otherwise ‘large’ size of tissue in this thesis. A typical problem with RFA for large target tissue is the incompleteness of tumour ablation, which is an important reason for tumour recurring. It is widely agreed that two reasons are responsible for the tumour recurring: (1) the tissue charring and (2) the ‘heat-sink’ effect of large blood vessels (i.e. ≥3 mm in diameter). This thesis study was motivated to more quantitatively understand tissue charring during the RFA procedure and to develop solutions to increase the size of target tissues to be ablated. The thesis study mainly performed three tasks: (1) evaluation of the existing devices and protocols to give a clear understanding of the state of arts of RFA devices in clinic, (2) development of an accurate mathematical model for the RFA procedure to enable a more quantitative understanding of the small target tissue size problem, and (3) development of a new protocol based on the existing device to increase the size of target tissues to be ablated based on the knowledge acquired from (1) and (2). In (1), a design theory called axiomatic design theory (ADT) was applied in order to make the evaluation more objective. In (2), a two-compartment finite element model was developed and verified with in vitro experiments, where liver tissue was taken and a custom-made RFA system was employed; after that, three most commonly used internally cooled RFA systems (constant, pulsed, and temperature-controlled) were employed to demonstrate the maximum size of tumour that can be ablated. In (3) a novel feedback temperature-controlled RFA protocol was proposed to overcome the small target tissue size problem, which includes (a) the judicious selection of control areas and target control temperatures and (b) the use of the tissue temperature instead of electrode tip temperature as a feedback for control. The conclusions that can be drawn from this thesis are given as follows: (1) the decoupled design in the current RFA systems can be a critical reason for the incomplete target tissue necrosis (TTN), (2) using both the constant RFA and pulsed RFA, the largest TTN can be achieved at the maximum voltage applied (MVA) without the roll-off occurrence. Furthermore, the largest TTN sizes for both constant RFA and pulsed RFA are all less than 3 cm in diameter, (3) for target tissues of different sizes, the MVA without the roll-off occurrence is different and it decreases with increase of the target tissue size, (4) the largest TTN achieved by using temperature-controlled RFA under the current commercial protocol is still smaller 3 cm in diameter, and (5) the TTN with and over 3 cm in diameter can be obtained by using temperature-controlled RFA under a new protocol developed in this thesis study, in which the temperature of target tissue around the middle part of electrode is controlled at 90 ℃ for a standard ablation time (i.e. 720 s). There are a couple of contributions with this thesis. First, the underlying reason of the incomplete TTN of the current commercially available RFA systems was found, which is their inadequate design (i.e. decoupled design). This will help to give a guideline in RFA device design or improvement in the future. Second, the thesis has mathematically proved the empirical conclusion in clinic that the limit size of target tissue using the current RFA systems is 3 cm in diameter. This has advanced our understanding of the limit of the RFA technology in general. Third, the novel protocol proposed by the thesis is promising to increase the size of TTN with RFA technology by about 30%. The new protocol also reveals a very complex thermal control problem in the context of human tissues, and solving this problem effectively gives implication to similar problems in other thermal-based tumour ablation processes

    Computer modeling of radiofrequency cardiac ablation: 30 years of bioengineering research

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    [EN] This review begins with a rationale of the importance of theoretical, mathematical and computational models for radiofrequency (RF) catheter ablation (RFCA). We then describe the historical context in which each model was developed, its contribution to the knowledge of the physics of RFCA and its implications for clinical practice. Next, we review the computer modeling studies intended to improve our knowledge of the biophysics of RFCA and those intended to explore new technologies. We describe the most important technical details of the implementation of mathematical models, including governing equations, tissue properties, boundary conditions, etc. We discuss the utility of lumped element models, which despite their simplicity are widely used by clinical researchers to provide a physical explanation of how RF power is absorbed in different tissues. Computer model verification and validation are also discussed in the context of RFCA. The article ends with a section on the current limitations, i.e. aspects not yet included in state-of-the-art RFCA computer modeling and on future work aimed at covering the current gapsGrant RTI2018-094357-B-C21 funded by MCIN/AEI/10.13039/501100011033 (Spanish Ministerio de Ciencia, Innovación y Universidades/Agencia Estatal de Investigación)González-Suárez, A.; Pérez, JJ.; Irastorza, RM.; D Avila, A.; Berjano, E. (2022). Computer modeling of radiofrequency cardiac ablation: 30 years of bioengineering research. Computer Methods and Programs in Biomedicine. 214:1-16. https://doi.org/10.1016/j.cmpb.2021.10654611621

    Thermal modeling of lesion growth with radiofrequency ablation devices

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    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
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