1,635 research outputs found

    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

    Computational Models and Experimentation for Radiofrequency-based Ablative Techniques

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    Las técnicas ablativas basadas en energía por radiofrecuencia (RF) se emplean con el fin de lograr un calentamiento seguro y localizado en el tejido biológico. En los últimos años ha habido un rápido crecimiento en el número de nuevos procedimientos médicos que hacen uso de dichas técnicas, lo cual ha ido acompañado de la aparición de nuevos diseños de electrodos y protocolos de aplicación de energía. Sin embargo, existen todavía muchas incógnitas sobre el verdadero comportamiento electro-térmico de los aplicadores de energía, así como de la interacción energía-tejido en aplicaciones concretas. El principal propósito de esta Tesis Doctoral es adquirir un mejor conocimiento de los fenómenos eléctricos y térmicos involucrados en los procesos de calentamiento de tejidos biológicos mediante corrientes de RF. Esto permitirá, por un lado, mejorar la eficacia y seguridad de las técnicas actualmente empleadas en la clínica en campos tan diferentes como la cirugía cardiaca, oncológica o dermatológica; y por otro, sugerir mejoras tecnológicas para el diseño de nuevos aplicadores. La Tesis Doctoral combina dos metodologías ampliamente utilizadas en el campo de la Ingeniería Biomédica, como son el modelado computacional (matemático) y la experimentación (ex vivo e in vivo). En cuanto al área cardiaca, la investigación se ha centrado, por una parte, en mejorar la ablación intraoperatoria de la fibrilación auricular por aproximación epicárdica, es decir, susceptible de ser realizada de forma mínimamente invasiva. Para ello, se ha estudiado mediante modelos matemáticos un sistema de medida de la impedancia epicárdica como método de valoración de la cantidad de grasa previo a la ablación. Por otra parte, se ha estudiado cómo mejorar la ablación de la pared ventricular por aproximación endocárdica-endocárdica (septo interventricular) y endocárdica-epicárdica (pared libre del ventrículo). Con este objetivo, se han comparado mediante modelado por computador la eficacia de los modos de ablación bipolar y unipolar en términos de la transmuralidad de la lesión en la pared ventricular. En lo que respecta al área de cirugía oncológica, la investigación se ha centrado en la resección hepática asistida por RF. Las técnicas de calentamiento por RF deberían ser capaces de minimizar el sangrado intraoperatorio y sellar vasos y ductos mediante la creación de una necrosis coagulativa por calentamiento. Si este calentamiento se produce en las cercanías de grandes vasos, existe un problema potencial de daño a la pared de dicho vaso. En este sentido, se ha evaluado con modelos matemáticos y experimentación in vivo si el efecto del flujo de sangre dentro de un gran vaso es capaz de proteger térmicamente su pared cuando se realiza una resección asistida por RF en sus cercanías. Además, se ha realizado un estudio computacional y experimental ex vivo e in vivo del comportamiento electro-térmico de aplicadores de RF bipolares internamente refrigerados, puesto que representan una opción más segura frente a los monopolares en la medida en que las corrientes de RF fluyen casi exclusivamente por el tejido biológico situado entre ambos electrodos. Respecto al área dermatológica, la investigación se ha centrado en mejorar el tratamiento de enfermedades o desórdenes del tejido subcutáneo (tales como lipomatosis, lipedema, enfermedad de Madelung y celulitis) mediante el estudio teórico de la dosimetría correcta en cada caso. Para ello, se han evaluado los efectos eléctricos, térmicos y termo-elásticos de dos estructuras diferentes de tejido subcutáneo durante el calentamiento por RF, y se ha cuantificado el daño térmico producido en ambas estructuras tras dicho calentamientoGonzález Suárez, A. (2014). Computational Models and Experimentation for Radiofrequency-based Ablative Techniques [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/36502TESI

    Index to NASA Tech Briefs, 1975

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    This index contains abstracts and four indexes--subject, personal author, originating Center, and Tech Brief number--for 1975 Tech Briefs

    Doctor of Philosophy

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    dissertationFor magnetic resonance-guided focused ultrasound (MRgFUS) treatments to be broadly accepted, progress must be made in treatment planning, monitoring, and control. A key component to this goal is accurate modeling of the bioheat transfer equation (BHTE). This dissertation develops new methods for identifying the significant parameters of the BHTE: the ultrasonic specific absorption rate (SAR), the tissue thermal diffusivity, and perfusion-related energy losses. SAR is determined by fitting an analytical solution one-dimensional radial Gaussian heating) to MRgFUS temperature data in simulations and a tissue-mimicking phantom. This new method is compared with linear and exponential methods for different fitting times, beam sizes, perfusion, and thermal diffusivity values. The analytical method is consistently most reliable and is accurate to within 10% for all cases, except high perfusion. An extension to the analytical solution improves SAR estimates for high perfusion cases. MRgFUS sampling characteristics (spatial averaging, temporal sampling, and noise) for SAR and thermal diffusivity estimation are parametrically evaluated against several focused ultrasound beam sizes. For single point heatings, a maximum voxel size of 1x1x3 mm is recommended for temperature and estimate errors to remain less than 10%. Two MRgFUS thermal diffusivity estimation methods are evaluated against a standard technique in ex vivo porcine and in vivo rabbit back muscle. Both methods accurately estimate thermal diffusivity using cooling data (overall ex vivo error < 6%, in vivo < 12%). Including heating data in the Gaussian SAR method further reduces errors (ex vivo error < 2%, in vivo < 3%). The Gaussian SAR method has better precision than the Gaussian temperature method. Two methods for quantifying perfusion-related energy losses using MRgFUS cooling temperatures are developed (experimental + modeled data vs. experimental data). The methods are verified via simulations and experiments in ex vivo perfused porcine kidney at different flow rates. The difference techniques employed make these methods susceptible to noise errors, but this feasibility study demonstrates promise for their use in future work. In conclusion, these methods can be used to validate biothermal models, and associated improvements in thermal modeling have the potential to increase the efficacy and safety of MRgFUS therapies

    Design and commissioning of an experiment for sympathetic cooling and coupling of ions in a cryogenic Penning trap

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    Precise comparisons between the properties of matter and antimatter conjugates constitute a stringent test of CPT and Lorentz symmetries. The proton’s and antiproton’s magnetic moments have recently been measured to high precision in Penning traps, but further progress is impaired by the need to prepare a particle with low motional energy. Current preparation schemes require long preparation times and are limited by high temperatures. Sympathetic laser cooling using an atomic ion has been proposed for preparation of low-energy protons and antipro- tons. This thesis presents the design and commissioning of a cryogenic Penning trap system for sympathetic laser cooling using beryllium ions. The experiment aims to demonstrate direct Coulomb coupling between two particles trapped in nearby, but separate potential wells in a Penning trap stack for the first time. This technique could be used for sympathetic cooling of particles lacking the necessary substructure to apply laser cooling directly. The application of this method on protons and antiprotons has the potential to decrease the mean kinetic energies of the particles and the preparation times required by several orders of magnitude. Furthermore, the method can be extended to other particles, such as highly charged ions. A quantum logic spectroscopy scheme for the measurement of the magnetic moment of the proton and antiproton has been proposed by Heinzen and Wineland. Experimental requirements for realisation of this proposal are discussed. The design of a suitable Penning trap system is described. A cryogenic ultra-high vacuum system cooled by a closed-cycle cryocooler, equipped with an ultra low vibration interface, is designed and commissioned. The necessary infrastructure, such as laser systems and electronics are described. First signals taken from this newly constructed cryogenic Penning trap are presented. Laser ablation trap loading, Doppler cooling and the reduction of the particle number down to a single ion are demonstrated. Prospects of the experiment and implications for the precision of future measurements of the proton’s and antiproton’s magnetic moments augmented by sympathetic laser cooling and elements of quantum logic are discussed

    Challenges to Validate Multi-physics Model of Liver Tumor Radiofrequency Ablation from Pre-clinical Data

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    International audienceThe planning and interventional guidance of liver tumor ra-diofrequency ablation (RFA) is difficult due to the cooling effect of large vessels and the large variability of tissue parameters. Subject-specific modeling of RFA is challenging as it requires the knowledge of model geometry and hemodynamics as well as the simulation of heat transfer and cell death mechanisms. In this paper, we propose to validate such a model from pre-operative multi-modal images and intra-operative signals (temperature and power) measured by the ablation device itself. In particular , the RFA computation becomes subject-specific after three levels of personalization: anatomical, heat transfer and a novel cellular necro-sis model. We propose an end-to-end pre-clinical validation framework that considers the most comprehensive dataset for model validation. This framework can also be used for parameter estimation and we evaluate its predictive power in order to fully assess the possibility to personalize our model in the future. Such a framework would therefore not require any necrosis information, thus better suited for clinical applications. We evaluated our approach on seven ablations from three healthy pigs. The predictive power of the model was tested: a mean point to mesh error between predicted and actual ablation extent of 3.5 mm was achieved

    An evaluation of the protective effect of an infusion of chilled glucosesolution on thermal injury of the bile ducts caused by radiofrequency ablation of the liver

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    PURPOSE: To evaluate the protective effects of chilling the bile ducts with cold (5°C) 5% glucose solution (GS) during radiofrequency (RF) administration. METHODS: Twenty male pigs (3 mos. old; 25-30 kg) were subjected to RF delivery with chilling (experimental group, N=10) or without chilling (control group, N=10). Half of the animals in each group were euthanized immediately after the operation, and half were euthanized one week later. The following histological variables in relation to the bile ducts were evaluated by a pathologist (blind examiner): degenerative changes to the epithelium; epithelial necrosis; ulceration, regenerative changes of the epithelium; polymorphonuclear neutrophil infiltration; and thermal effects. RESULTS: The experimental group (88 bile ducts examined) showed reduced thermal damage relative to the control group (86 bile ducts examined) as demonstrated by significant differences in the following histopathological parameters: epithelial detachment of biliary epithelium (84.1% vs. 59.3%; p<0.006); elongation/palisade arrangement of nuclei (65.1% vs. 87.5%; p<0.001); pseudo-goblet cells (32.9% vs. 56.8%; p<0.001). CONCLUSION: Infusion of 5% glucose solution (5°C) has a protective effect on bile duct subjected to heat (95-110°C, 12 min) from radiofrequency thermal ablation device.Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Federal University of São PauloUniversidade Federal de São Paulo (UNIFESP) Department of PathologyUniversidade Federal de São Paulo (UNIFESP) Department of SurgeryAlbert Einstein Israelite Hospital Department of Image DiagnosticUNIFESP School of MedicineUNIFESP, Department of PathologyUNIFESP, Department of SurgeryUNIFESP, School of MedicineSciEL

    Modélisation de l’ablation radiofréquence pour la planification de la résection de tumeurs abdominales

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    The outcome of radiofrequency ablation (RFA) of abdominal tumors is challenged by the presence of blood vessels and time-varying thermal conductivity, which make patient-specific planning extremely difficult. By providing predictive tools, biophysical models may help clinicians to plan and guide the procedure for an effective treatment. We introduce a detailed computational model of the biophysical mechanisms involved in RFA of hepatic tumors such as heat diffusion and cellular necrosis. It simulates the extent of ablated tissue based on medical images, from which patient-specific models of the liver, visible vessels and tumors are segmented. In this thesis, a new approach for solving these partial differential equations based on the Lattice Boltzmann Method is introduced. The model is first evaluated against clinical data of patients who underwent RFA of liver tumors. Then, a comprehensive pre-clinical experiment that combines multi-modal, pre- and post-operative anatomical and functional images, as well as the interventional monitoring of the temperature and delivered power is presented. This enables an end-to-end validation framework that considers the most comprehensive data set for model validation. Then, we automatically estimate patient-specific parameters to better predict the ablated tissue. This personalization strategy has been validated on 7 ablations from 3 clinical cases. From the pre-clinical study, we can go further in the personalization by comparing the simulated temperature and delivered power with the actual measurements during the procedure. These contributions have led to promising results, and open new perspectives in RFA guidance and planning.L'ablation par radiofréquence (ARF) de tumeurs abdominales est rendue difficile par l’influence des vaisseaux sanguins et les variations de la conductivité thermique, compliquant la planification spécifique à un patient donné. En fournissant des outils prédictifs, les modèles biophysiques pourraient aider les cliniciens à planifier et guider efficacement la procédure. Nous introduisons un modèle mathématique détaillé des mécanismes impliqués dans l’ARF des tumeurs du foie comme la diffusion de la chaleur et la nécrose cellulaire. Il simule l’étendue de l’ablation à partir d’images médicales, d’après lesquelles des modèles personnalisés du foie, des vaisseaux visibles et des tumeurs sont segmentés. Dans cette thèse, une nouvelle approche pour résoudre ces équations basée sur la méthode de Lattice Boltzmann est introduite. Le modèle est d’abord évalué sur des données de patients qui ont subi une ARF de tumeurs du foie. Ensuite, un protocole expérimental combinant des images multi-modales, anatomiques et fonctionnelles pré- et post-opératoires, ainsi que le suivi de la température et de la puissance délivrée pendant l'intervention est présenté. Il permet une validation totale du modèle qui considère des données les plus complètes possibles. Enfin, nous estimons automatiquement des paramètres personnalisés pour mieux prédire l'étendu de l’ablation. Cette stratégie a été validée sur 7 ablations dans 3 cas cliniques. A partir de l'étude préclinique, la personnalisation est améliorée en comparant les simulations avec les mesures faites durant la procédure. Ces contributions ont abouti à des résultats prometteurs, et ouvrent de nouvelles perspectives pour planifier et guider l’ARF
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