30 research outputs found

    بررسی و شبيه‌سازی LITT در بافت بيولوژيکی با روش المان مرزی دو‌جانبه‌ای

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    چکيده مقاله: مقدمه: گرما درمانی بينابينی القا شده توسط ليزر [1] (LITT) يک روش گرما درمانی به صورت حداقل تهاجمی برای درمان تومور‌های سرطانی است. مدل کردن اثر ليزر بر بافت در LITT مزيت‌های زيادی نسبت به روش‌های نظارت بر افزايش دما دارد از جمله بررسی انتشار نور و انتقال گرما، تغيير پارامتر‌های تاثير‌گذار در اثر ليزر بر بافت و هزينه کمتر و به صرفه بودن. از ميان روش‌های گوناگون حل عددی مانند المان محدود و تفاضل محدود، روش المان مرزی دو‌جانبه‌ای جديدترين روش مورد استفاده محققان برای حل مسائل انتقال گرما در بافت است. روش بررسی: در اين تحقيق افزايش دمای بافت کبد با روش المان مرزی دوجانبه‌ای بررسی شده است. در اين مقاله از روش مونت کارلو با گام متغيير و جذب تدريجی برای انتشار نور در بافت استفاده شده است. همچنين نتايج حاصل از روش المان مرزی دوجانبه‌ای با روش المان محدود مقايسه شده است. يافته‌ها: نتايج نشان می‌دهد که هر دو روش المان مرزی دوجانبه‌ای و المان محدود به نتايج تقريبا مشابهی می‌رسند و اختلاف دمای اين دو روش ناچيز و کمتر از 1 درجه سانتی‌گراد است. همچنين روش المان مرزی به علت کاهش يک واحدی بعد مسئله باعث افزايش سرعت حل می‌شود. نتيجه‌گيری: روش المان مرزی دوجانبه‌ای روشی دقيق و سريع برای برای بررسی انتقال گرما در بافت در اثر تابش ليزری می‌باشد

    A New Boundary Element Technique For One- And Two-Temperature Models Of Biothermomechanical Behavior Of Anisotropic Biological Tissues

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    The main objective of this paper is to develop a novel boundary element technique for describing the three-dimensional (3D) biothermomechanical behavior of anisotropic biological tissues. The governing equations are studied on the basis of the dual phase lag bioheat transfer and Biot's theory for oneand two-temperature models. Because of the benefits of CQBEM, such as not being restricted by the complex shape of biological tissues and not requiring discretization of the interior of the treated region, it can cope with complex bioheat models and has low use of RAM and CPU. CQBEM is therefore a flexible and efficient tool for modeling the distribution of bioheat in anisotropic biological tissues and associated deformation. The resulting linear equations arising from CQBEM are solved by the generalized modified shift-splitting (GMSS) iterative method which reduces the number of iterations and the total time of the CPU. Numerical findings show the validity, efficacy and consistency of the proposed technique

    Transient bioheat transfer analysis in biological tissues by fundamental-solution-based numerical methods

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    Taylor's expansion approach was applied to linearize the nonlinear term in the original nonlinear bioheat transfer governing equation. Then the DRM and the MFS was established to obtain the particular and homogeneous solutions. The influence of blood perfusion rate on temperature distribution in the skin tissue was analysed by changing the coefficients in the three expressions of blood perfusion rate. Numerical results showed that the variation of blood perfusion rate plays a significant role in the temperature distribution within the skin tissue. Finally, a meshless numerical scheme combining the operator splitting method (OSM), the RBF interpolation and the MFS was developed for solving transient nonlinear bioheat problems in two-dimensional skin tissue. In the numerical scheme, the nonlinearity caused by the temperature-dependent blood perfusion rate (TDBPR) is taken into consideration. In the procedure, the OSM is used to separate the Laplacian operator and the nonlinear source term, and then second-order time-stepping schemes are employed for approximating two splitting operators in order to convert the original governing equation into a linear nonhomogeneous Helmholtz-type governing equation (NHGE) at each time step. The full fields consisting of the particular and homogeneous solutions are enforced to fit the NHGE at interpolation points and the boundary conditions at boundary collocations to determine unknowns at each time step. The proposed method was verified by comparison with other methods. Furthermore, the sensitivity of the coefficients in cases of a linear and an exponential relationship of TDBPR was investigated to reveal their bioheat effect on the skin tissue

    Target-specific multiphysics modeling for thermal medicine applications

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    Dissertation to obtain the degree of Doctor of Philosophy in Biomedical EngineeringThis thesis addresses thermal medicine applications on murine bladder hyperthermia and brain temperature monitoring. The two main objectives are interconnected by the key physics in thermal medicine: heat transfer. The first goal is to develop an analytical solution to characterize the heat transfer in a multi-layer perfused tissue. This analytical solution accounts for important thermoregulation mechanisms and is essential to understand the fundamentals underlying the physical and biological processes associated with heat transfer in living tissues. The second objective is the development of target-specific models that are too complex to be solved by analytical methods. Thus, the software for image segmentation and model simulation is based on numerical methods and is used to optimize non-invasive microwave antennas for specific targets. Two examples are explored using antennas in the passive mode (probe) and active mode (applicator). The passive antenna consists of a microwave radiometric sensor developed for rapid non-invasive feedback of critically important brain temperature. Its design parameters are optimized using a power-based algorithm. To demonstrate performance of the device, we build a realistic model of the human head with separate temperaturecontrolled brain and scalp regions. The sensor is able to track brain temperature with 0.4 °C accuracy in a 4.5 hour long experiment where brain temperature is varied in a 37 °C, 27 °C and 37 °C cycle. In the second study, a microwave applicator with an integrated cooling system is used to develop a new electro-thermo-fluid (multiphysics) model for murine bladder hyperthermia studies. The therapy procedure uses a temperature-based optimization algorithm to maintain the bladder at a desired therapeutic level while sparing remaining tissues from dangerous temperatures. This model shows that temperature dependent biological properties and the effects of anesthesia must be accounted to capture the absolute and transient temperature fields within murine tissues. The good agreement between simulation and experimental results demonstrates that this multiphysics model can be used to predict internal temperatures during murine hyperthermia studies

    Heat Transfer

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    Over the past few decades there has been a prolific increase in research and development in area of heat transfer, heat exchangers and their associated technologies. This book is a collection of current research in the above mentioned areas and describes modelling, numerical methods, simulation and information technology with modern ideas and methods to analyse and enhance heat transfer for single and multiphase systems. The topics considered include various basic concepts of heat transfer, the fundamental modes of heat transfer (namely conduction, convection and radiation), thermophysical properties, computational methodologies, control, stabilization and optimization problems, condensation, boiling and freezing, with many real-world problems and important modern applications. The book is divided in four sections : "Inverse, Stabilization and Optimization Problems", "Numerical Methods and Calculations", "Heat Transfer in Mini/Micro Systems", "Energy Transfer and Solid Materials", and each section discusses various issues, methods and applications in accordance with the subjects. The combination of fundamental approach with many important practical applications of current interest will make this book of interest to researchers, scientists, engineers and graduate students in many disciplines, who make use of mathematical modelling, inverse problems, implementation of recently developed numerical methods in this multidisciplinary field as well as to experimental and theoretical researchers in the field of heat and mass transfer

    The results of a unique Nordic HAKK interlaboratory REAT comparison

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    Antenna Systems

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    This book offers an up-to-date and comprehensive review of modern antenna systems and their applications in the fields of contemporary wireless systems. It constitutes a useful resource of new material, including stochastic versus ray tracing wireless channel modeling for 5G and V2X applications and implantable devices. Chapters discuss modern metalens antennas in microwaves, terahertz, and optical domain. Moreover, the book presents new material on antenna arrays for 5G massive MIMO beamforming. Finally, it discusses new methods, devices, and technologies to enhance the performance of antenna systems

    A numerical method for obtaining an optimal temperature distribution in a three-dimensional triple-layered skin structure embedded with multi-level blood vessels

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    The research related to hyperthermia has stimulated a lot of interest in recent years because of its application in cancer treatment. When heating the tumor tissue, the crucial problem is keeping the temperature of the surrounding normal tissue below a certain threshold in order to avoid the damage to the normal tissue. Hence, it is important to obtain the temperature field of the entire region during the treatment. The objective of this dissertation is to develop a numerical method for obtaining an optimal temperature distribution in a 3D triple-layered skin structure embedded with multi-level blood vessels where the surface of the skin is irradiated by laser. The skin structure is composed of epidermis, dermis and subcutaneous, while the dimension and blood flow of the multi-level blood vessels are determined based on the constructal theory of multi-scale tree-shaped heat exchangers. The method determines the optimal laser intensity to obtain prespecified temperatures at the given locations of the skin after a pre-specified laser exposure time under a pre-specified laser irradiation pattern. The modified Pennes bio-heat transfer model is employed to describe the thermal behavior for tissue coupled with the convective energy balance equations for blood. The finite difference schemes for solving these equations are developed and the least squares method is used to optimize the laser power. As such, we develop an algorithm which can be used to obtain an optimal temperature distribution. Furthermore, the preconditioned Richardson iteration and Thomas algorithm are employed to speed up and simplify the computation. To demonstrate the applicability of the mathematical model and the numerical method, we test on three examples in each of which two cases are considered. The numerical examples show that the method is applicable and efficient. This research is important since the results will provide the clinician with powerful tools to improve the ability to deliver safe and effective therapy and the means to assess treatment safety, efficacy, and clinical outcome for skin, head, and neck cancer treatments

    Modelling, Simulation and Data Analysis in Acoustical Problems

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    Modelling and simulation in acoustics is currently gaining importance. In fact, with the development and improvement of innovative computational techniques and with the growing need for predictive models, an impressive boost has been observed in several research and application areas, such as noise control, indoor acoustics, and industrial applications. This led us to the proposal of a special issue about “Modelling, Simulation and Data Analysis in Acoustical Problems”, as we believe in the importance of these topics in modern acoustics’ studies. In total, 81 papers were submitted and 33 of them were published, with an acceptance rate of 37.5%. According to the number of papers submitted, it can be affirmed that this is a trending topic in the scientific and academic community and this special issue will try to provide a future reference for the research that will be developed in coming years

    Agent-based modelling of tumour spheroid growth and treatment

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    Malignant neoplasms are one of the top causes of death in all developed countries around the world and account for almost one quarter of all deaths. An individual cell based computational model with strong connections to the experimental data through lattice free, newtonian interaction could be used to validate experimental results and eventually make predictions guiding further experiments. This model was build as a part of the thesis and shall be extended to the modelling of the effects of ionic radition on the vascularised tumour as a possible treatment for inoperable tumours.Im Rahmen dieser Diplomarbeit wurde eine, von der individuellen Zelle ausgehende, agentenbasierte Computersimulation des Wachstums eines multizellulären Tumorsphäroiden entwickelt. Die theoretische Behandlung des Tumorwachstums ist von großem Interesse, da ein realistisches Modell dazu dienen kann, Experimente in silico zu simulieren. Dies bietet nicht nur zeitliche und finanzielle Vorteile gegenüber der tatsächlichen Durchführung der Experimente, sondern muss auch von einem ethischen Standpunkt aus bevorzugt werden, da Simulationen Laborversuche an Tieren oder klinische Tests an Probanden teilweise ersetzen können. Die Simulationsumgebung, welche als Teil dieser Diplomarbeit entwickelt wurde, ist in der Programmiersprache C++ erstellt, um durch die verwendung von Objekten und Klassen eine maximale Erweiterbarkeit im Hinblick auf zukünftige Untersuchungen zu gewährleisten. Eine starke experimentelle Anbindung ist durch die gitterfreie, kräftebasierte Interaktion der Zellagenten gegeben. Die Tumordynamik inklusive Zellbewegung, Zellzyklus und Diffusion von Nährstoffen wurde als Multiskalenproblem erfasst. Um eine realistische Simulation zu erstellen, muss die Zelle als das zu simulierende Objekt zuerst abstrahiert werden. Dabei geht es um die realitätsgetreue Abbildung der biophysikalisch relevanten Eigenschaften einer Zelle auf ein mathematisches Modell. Mechanismen der Zelle, die für eine realistische Erforschung der Onkogenese im Modell entscheident sind, müssen im Modellansatz implementiert werden. In erster Näherung kann eine Zelle als viskoelastische, adhäsive Kugel betrachtet werden. Folgt man dieser Betrachtungsweise so sind etablierte Interaktionsmodelle wie zum Beispiel das Johnson-Kendall-Roberts Modell anwendbar, um die Wechselwirkung zwischen Zellen realistisch zu beschreiben. Zur Bestimmung der Zellnachbarschaft wurde eine kinetische und dynamische Delaunay-Triangulation verwendet, welche es ermöglicht, auf elegante und effiziente Weise die Nachbarschaftsbeziehungen im Gewebe zu erfassen, sowie durch ihre Dualität zur Voronoi-Zerlegung Zellvolumina und -kontaktflächen zu berechnen. Die aus dem Johson-Kendall-Roberst Modell resultierenden Kräfte der Zellinteraktion wurden in einer überdämpften Näherung integriert, wie sie für Zellen in dichtem Gewebe anwendbar ist. Hierzu wurden numerischen Algorithmen für die Stabilisierung und effizientere Simulation der entstehenden Zelldynamik entwickelt (lokale und globale adaptive Zeitschrittweite). Die Einführung eines Zellzyklus und der dazugehörigen Mechanismen für die Zellagenten ermöglicht die realistische Simulation des Gewebewachstums. Voraussetzung dafür war, das die Dynamik der Nährstoffe für den Zellmetabolismus erfasst werden konnte. Zur Modellierung der zugrunde liegenden Reaktions-Diffusionssysteme löslicher Nährstoffe wird der "alternating-direction implicit"-Algorithmus (ADI) angewandt. Weiterhin wurde ein fortschrittlicher Algorithmus für die Zytokinese in agentenbasierten Simulationen eingeführt, der entscheidende Laufzeitvorteile durch eine realistischere Dynamik der Zellen während der Mitose mit sich bringt. Ein implementiertes Modell für die mechanische Proliferationshemmung infolge eines zu hohen Zelldrucks wurde mit der Wirkung eines nährstoffbasierten Mechanismus verglichen. Das Wachstum eines multizellulären Tumorsphäroiden konnte im Verlauf der Arbeit auf der Basis von experimentell ermittelten Größen für die Zellagenten in silico modelliert werden. Dabei wurde ein Vergleich der erzielten Ergebnisse mit experimentellen Resultaten durchgeführt. Sowohl für das Problem der Zellsortierung aufgrund differentieller Adhäsion als auch für das avaskuläre Tumorwachstum, stimmten die Ergebnisse des Modells mit den experimentellen Resultaten überein. Erste Simulatioinen der Bestrahlung eines Tumors in silico zeigten Effekte wie z.B. die Arretierung am G2=M-Kontrollpunkt, die qualitativ wie quantitativ mit experimentellen Beobachtungen übereinstimmen. Als Reaktion der Tumordynamik auf partielle Bestrahlung des Gewebes wurden verschiedene Phänomene beobachtet, die für weitere Untersuchungen von Interesse sind. Dazu zählen Effekte wie z.B. die Resynchronisierung des Zellzyklus und ein exzessives Tumorwachstum nach erfolgter Bestrahlung. Die Übereinstimmung der erzielten Ergebnisse zeigt, dass das entwickelte Modell auf die Simulation von komplexeren Effekten der Tumorbestrahlung mit Schwerionen ausgedehnt werden kann. Eine angestrebte Nutzung ist die Simulation der Bestrahlungsprozesse mit dem Ziel, die verwendeten Protokolle zu optimieren und damit die Effektiviät der Strahlentherapie zu erhöhen
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