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LACERDA, FELIPE CERQUEIRA DE. "MEANING OF HOMEOWNERSHIP FOR THE MIDDLE CLASS IN THE MRV DISCOURSE." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2016. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=27664@1.
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Nos últimos anos, verificou-se notável crescimento do consumo da classe média brasileira que proporcionou a essa classe maior acesso na compra da casa própria. A aquisição da casa própria constitui um sonho de consumo desse extrato social e apresenta grande conotação simbólica. A construtora MRV, líder no segmento de imóveis para a classe média, com ênfase na oferta de imóveis com o perfil de primeiro apartamento do consumidor, destaca-se por suas estratégias de comunicação e por seu discurso publicitário. Neste contexto, o presente trabalho tem por objetivo identificar os significados que a compra da casa própria assume no discurso da construtora MRV em seus canais digitais. Para tal, analisou-se um corpus de vinte vídeos produzidos pela MRV e publicados em seu canal no YouTube entre os meses de Janeiro e Novembro de 2015. A abordagem da pesquisa foi qualitativa e exploratória, com utilização de análise textual verbal e visual do corpus, bem como de técnicas de análise de conteúdo. Os vídeos foram classificados em quatro categorias temáticas, a saber: Venda de Novos Empreendimentos, Entrega das Chaves, Histórias de vida de clientes MRV e Institucionais. O resultado do estudo apontou que no discurso analisado a casa própria assume diferentes significados, como: realização, identidade, independência, segurança e pertencimento. Com base na axiologia de valores de consumo proposta pelo semioticista J.M.Floch, tais significados revelam a prevalência de valores práticos, críticos e utópicos no discurso da construtora MRV.In recent years, there has been remarkable growth of the Brazilian middle class consumption provided to this class greater access in buying a home. The acquisition of a home is a dream of consumption of this social stratum and has great symbolic connotation. MRV construction company, leader in the real estate segment for the middle class, with an emphasis on real estate supply to the first consumer flat profile, stands out for its communication strategies and their advertising discourse. In this context, this paper aims to identify the meanings that home ownership plays in the builder MRV discourse in their digital channels. To do this, we analyzed a corpus of twenty videos produced by MRV Company and published on his YouTube channel between January and November 2015. The research approach was qualitative and exploratory, using verbal and visual textual analysis of the corpus and content analysis techniques. The videos were classified into four themes, namely: Sale of New Ventures, Delivery of the Keys, Customer Life Stories MRV and Institutional. The study results showed that in the discourse examined the house itself takes on different meanings, such as: holding, identity, independence, security and belonging. Based on the axiology of consumption values proposed by J.M.Floch semiotician such meanings reveal the prevalence of practical, critical and utopian values on the MRV discourse.
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Visa, Codrut Ion Alin. "Commande non linéaire et observateurs : application à la MRV en grande vitesse." Metz, 2004. http://www.theses.fr/2004METZ026S.
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Ce travail concerne la commande en boucle fermée d'une machine à réluctance variable (MRV) destinée à l'usinage à grande vitesse. Le principe de fonctionnement d'une MRV 6/2 et sa modélisation sont d'abord présentés. Le développement d'une commande à la fois performante et robuste dépend de la connaissance de paramètres du modèle de la MRV. L'identification sans capteur de position des paramètres de la MRV a permis d'obtenir la caractéristique électromagnétique et les paramètres mécaniques. Des phénomènes de frottement hydrodynamiques et aérodynamiques ont été mis en évidence. Le caractère fortement non linéaire d'une MRV rend son contrôle difficile. La commande en boucle fermée de la MRV à basse vitesse a montré l'intérêt de l'emploi d'une commande non linéaire linéarisante par retour d'état. Toutefois à grande vitesse, plusieurs phénomènes spécifiques limitent les performances de la MRV en boucle fermée. Ces phénomènes sont analysés à travers les résultats des simulations de commandes non linéaires linéarisante en tension et en courant. En présence d'un capteur de position un observateur à entrée inconnue est développé et expérimenté. Afin de palier le manque de capteur performant à grande vitesse, nous avons développé un observateur non linéaire d'ordre réduit. Enfin, un système de commande a été réalisé pour expérimenter les algorithmes de commande. Le système d'exploitation Linux temps réel (RTAI) combiné avec des cartes d'acquisition entrées-sorties nous a permis d'obtenir un fonctionnement avec une période d'échantillonnage de 10s. L'interface graphique et l'acquisition des données sont gérées par des processeurs distinctsThis work deals with the closed loop control of a switched reluctance motor (SRM) used for high speed machining. The principle of operation of a 6/2 SRM and its model are firstly presented. The design of a performant and robust control law depends on the knowledge of the SRM model parameters. Sensorless position parameters identification has allowed to obtain the electromagnetic characteristic and the mechanical parameters. Hydrodynamic and aerodynamic friction phenomena have been highlighted. The highly nonlinear character of the SRM makes the control difficult. The closed loop control of the SRM running at low speed showed the interest of using the feedback linearizing control technique. However at high speed, several specific problems limit the drive performances in the closed loop. The main aspects of a high speed running SRM have been analysed through the results of the simulations of feedback linearizing voltage and current control law. When the position information is available, an unknown input observer has been developed and experimented. In order to tackle the lack of a performant position sensor at high speed, a nonlinear reduced order observer has been studied. Finally, a real time control system has been realized in order to test the control laws. Real time Linux (RTAI) operating system combined with the data acquisition boards have allowed to obtain 10s sampling frequency behavior of the control system. The graphical interface and data acquisition are executed by distinct processors
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Qin, Qingsong. "Characterization of mammalian orthoreovirus (MRV) induced stress granules (SGs) and implications of eIF2[alpha] phosphorylation on viral translation." [Ames, Iowa : Iowa State University], 2010. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3403826.
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Besbes, Mondher. "Contribution à la modélisation numérique des phénomènes couples magneto-élastiques : Application à l'étude des vibrations d'origine magnétique dans les MRV." Paris 6, 1995. http://www.theses.fr/1995PA066023.
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Les travaux présentés dans ce mémoire traitent de la modélisation numérique dans l'hypothèse bidimensionnelle des phénomènes couples magneto-elastiques dans les dispositifs electromagnetiques. L'objectif est particulièrement cible a l'étude théorique et expérimentale des vibrations d'origine magnétique dans les machines a reluctance variable a double saillance. Dans le but de quantifier la réponse vibratoire d'une telle machine, nous avons introduit dans un code de calcul du champ magnétique, base sur la méthode des éléments finis, un module qui permet la détermination de la répartition des forces magnétiques locales pour calculer les déformations mécaniques résultantes. Le choix de la méthode de calcul de force magnétique, qui se base sur l'application locale du principe des travaux virtuels, a été justifie par la précision de cette méthode, sa generalite (milieux satures) et sa souplesse de mise en ouvre. L'analyse spectrale des forces magnétiques nous a permis de prédire quelles sont les modes de vibrations qui vont être excites. Le calcul du spectre des vibrations a été réalise en cherchant la solution de l'équation d'équilibre relative a chaque harmonique de force. Une analyse modale a été aussi effectuée pour déterminer les fréquences de résonance et les modes de vibrations associées. Parallèlement a cette approche numérique, nous avons analyse expérimentalement, en se basant sur des mesures accelerometriques, le comportement vibratoire de la machine. Grâce a cette analyse, nous avons pu valider le code de calcul des vibrations ainsi développe. L'ensemble de ces travaux a montre que la source principale du bruit acoustique, ou des vibrations qui le produisent, dans la machine d'étude réside sur l'action des forces magnétiques radiales d'attraction des dents statoriques et rotoriques en particulier lorsque celles-ci sont en conjonction. A la fin de ce mémoire, nous avons mis au point un modèle de couplage fort qui permet la résolution simultanée des problèmes couples magneto-elastiques. Ce type de modèle trouve son importance dans le cas ou les propriétés magnétiques et élastiques sont en forte interaction. Nous avons spécialement évoque dans cette partie le calcul des déformations des matériaux fortement magnétostrictifs et la résolution des problèmes de grandes déformations élastiques
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Sarr, Abdoulaye. "Amélioration de la sûreté de fonctionnement d’un actionneur électrique à réluctance variable." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS533/document.
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Le travail proposé dans cette thèse porte sur l’amélioration de l’efficacité énergétique et de la sûreté de fonctionnement de la Machine à Réluctance Variable (MRV). D’abord, nous avons présenté la commande de la MRV en modes moteur et générateur débitant sur bus continu. Pour le mode moteur, on cherche à réguler la vitesse de rotation et le couple, alors qu’en mode générateur, l’objectif de la commande est de maintenir constante la tension du bus malgré les fluctuations de la vitesse et de la charge. Une démarche itérative est proposée pour la maximisation du rendement global. Trois paramètres de réglage ont été choisis : L’angle d’amorçage (Ψ), l’angle de conduction (Θp) et le courant de référence des phases (Iref). L’efficacité de l’algorithme est évaluée à travers des simulations et des tests expérimentaux. Un rendement global maximal de 70% est atteint pour des vitesses et couples élevés. Ensuite, on s’est intéressé à la connexion de la Génératrice à Réluctance Variable (GRV) au réseau alternatif monophasé ou triphasé dans le cadre d’une application éolienne. La tension continue à la sortie de la GRV est convertie en une tension alternative par un convertisseur DC-AC. Le premier objectif est de maintenir la tension du bus continu à sa valeur nominale; le second est de contrôler la qualité du courant injecté dans le réseau. En monophasé, trois types de correcteur sont testés pour réguler le courant sinusoïdal (un correcteur PI, un correcteur Résonant et un correcteur Proportionnel-Résonant). En triphasé, une commande VQ dans le référentiel de Park est adoptée: La tension du bus continu est contrôlée à travers le courant id et la puissance réactive est contrôlée par le courant iq. Les résultats de simulation montrent qu’on obtient des courants quasi-sinusoïdaux avec un taux de distorsion harmonique inférieur à 1% aussi bien en monophasé qu’en triphasé. Enfin, pour améliorer la sûreté de fonctionnement de l’actionneur et réduire les coûts liés à l’utilisation de capteurs mécaniques, trois stratégies de commande sans capteur de position sont présentées. La première est basée sur la technique d’injection. La deuxième repose sur l’estimation du flux. La troisième s’appuie sur les observateurs adaptatifs. On trouve que la technique d’injection et la méthode basée sur la mesure du flux fonctionnent de façon complémentaire. La première est efficace en basses vitesses et ne dépend pas de la charge, la deuxième est performante en hautes vitesses et pour des charges élevées. L’observateur adaptatif proposé assure une convergence exponentielle de la position malgré le modèle analytique simplifié de l’inductance utilisé pour la synthèse. Son principal avantage réside dans sa robustesse aux variations paramétriques et au couple de charge qui est estiméThe work proposed here focuses on the improvement of the energy efficiency and the safety of the Switched Reluctance Machine (SRM). First, the control of the SRM in motor and generator modes is presented. In motor mode, the speed and the torque are regulated, while in generator mode, the objective is to keep constant the DC bus voltage. An iterative optimization algorithm is proposed formaximizing the global efficiency. The analysis of the electromechanical energy conversion has shown that there is an optimal combination of the control variables - turn on angle (Ψ), conduction angle (Θp) and reference current (Iref) – to maximize the efficiency. The strategy is evaluated using intensive numerical simulations and experimental validation. Thanks to the optimization, the global efficiency reaches 70% almost from half the nominal speed to the maximum speed. Then, the Switched Reluctance Generator (SRG) is used as an AC generator for a Wind Energy Conversion (WEC) application. The produced DC power is converted into AC power by means of voltage inverter and delivered to the AC grid. The first issue of the WEC control is to maintain constant the output DC voltage despite the wind speed variations and the load uncertainty. The second issue is to control the quality of the current. In single-phase AC network, three controllers are tested to regulate the AC current (PI controller, Resonant controller, Proportional-Resonant controller). In three-phase AC network, a VQ control in Park’s frame is adopted: The DC bus voltage is controlled through the direct current and the reactive power injected into the grid is controlled through the quadrature current. Simulation results show that quasi-sinusoidal currents with a harmonic distortion rate less than 1% are obtained in both cases. Finally, we address the problem of sensorless control. In fact, the control of the SRM requires that the rotor position is known. A mechanical encoder is used generally to measure the position. The elimination of this position sensor would reduce the cost and packaging requirements of the drive. Three methods to estimate the rotor position are presented. The first one named inductance-method is an active as it is based on the pulse injection technique. The second one named flux-method is a passive one as it used the current measurement. The third one is based on the state observers for the flux, position, and velocity and load torque estimation. The simulations results have shown that the inductance-based method is efficient in low speed region and the flux-based one is more efficient in high-speed region. It is also shown that, observers are exponentially convergent even when a simple analytical modelling, that neglects saturation effect, is used to design the observer
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Slovak, Peter Michael. "Characterisation of the mre and mrd loci of Rhodobacter sphaeroides." Thesis, University of Oxford, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.414270.
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Inturi, Satya Prakash Reddy, and Chaitanya Macherla. "System Performance of MIMO MRT/MRC System under Perfect CSI." Thesis, Blekinge Tekniska Högskola, Institutionen för datavetenskap, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-21137.
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Multiple Input and Multiple Output (MIMO) is one of the techniques used tiimprove the system performance. In this thesis, we improve and evaluate the system performance of MIMO deploying MRT technique at the transmitter and MRCtechnique at the receiver with an assuming that the system can obtain perfect CSI.We derived expressions for outage probability and symbol error rate and simulationgraphs for SISO, SIMO, MISO, and MIMO in terms of outage probability. Our results show that the MIMO system performance is better than other configurations.We also observed that SISO have the least performance where SIMO and MISOhave same performance. The performance also increases as the number of antennasincrease in the system and it is suggested to use MIMO when performance is givehigh priority than cost.
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Chalmers, Kirsten Hardie. "Fluorinated paramagnetic probes for 19-F and 1-H MRS/MRI." Thesis, Durham University, 2011. http://etheses.dur.ac.uk/879/.
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Novel CF3-labelled lanthanide(III) complexes have been synthesised for use as probes for 19-F and 1-H magnetic resonance spectroscopy and imaging. The syntheses and evaluation of two classes of fluorinated paramagnetic complexes are defined. Notably, the 19-F magnetic resonance relaxation processes for the complexes have been assessed, allowing for the analysis of the interplay between applied field, Ln(III) ion and rotational correlation time on relaxation properties. Strategies employed to enhance signal intensity are discussed, examining a number of different of fluorinated mono- and di-amide cyclen ligands. Systems incorporating phosphinate pendant arms are of particular interest, resulting in complexes with favourable isomer distributions, faster longitudinal relaxation rates and narrower linewidths. Finally, the synthesis of high molecular weight conjugates with paramagnetic fluorinated complexes is described. Three different classes of medium to high molecular adducts were considered, with the merits and limitations of each assessed. The desirable formation of one species in solution, ease of solubility and attractive 19F and 1H relaxometric properties render the chitosan conjugates promising candidates for future use as imaging probes.
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Ramamurthy, Senthil. "Localized double-quantum filtered correlated spectroscopy on 3T MRI/MRS scanner." Morgantown, W. Va. : [West Virginia University Libraries], 2005. https://etd.wvu.edu/etd/controller.jsp?moduleName=documentdata&jsp%5FetdId=4012.
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Thesis (M.S.)--West Virginia University, 2005.Title from document title page. Document formatted into pages; contains ix, 69 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 65-69).
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Chao, Hui Ph D. Massachusetts Institute of Technology. "Multi-echo methods for fast MRI and MRS of ³¹P containing compounds." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/43335.
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Chen, Hua Hsuan. "The application of MRI and MRS in psychiatry and performance evaluation of magnetic field homogeneity in MRI : a dissertation /." San Antonio : UTHSC, 2006. http://proquest.umi.com/pqdweb?did=1155567931&sid=1&Fmt=2&clientId=70986&RQT=309&VName=PQD.
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Catata, Elmer Osman Hancco. "Controlador PI FUZZY aplicado ao controle direto de potência do gerador de relutância variável de 12/8 conectado à rede elétrica." reponame:Repositório Institucional da UFABC, 2016.
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Orientador: Prof. Dr. José Luis Azcue PumaDissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Engenharia Elétrica, 2016.
Este trabalho apresenta o controle direto de potencia do gerador de relutancia variavel de 12/8 utilizando o controlador fuzzy PI auto-ajustavel e o controle vetorial do inversor conectado à rede eletrica. Inicialmente são estudados os principios de operação da maquina e a topologia do conversor eletronico de potencia que sera utilizado para aciona-lo. Usando o software de simulaçãoMatlab/Simulink é implementado o modelo da maquina de relutancia variavel utilizando as curvas caracteristicas, de corrente e torque, que foram extraídas utilizando dados experimentais. Utilizando o modelo da maquina é projetado o controlador de velocidade para sua operação no modo motor. Tambem sera projetado o controlador de potência PI utilizando o modelo estimado do sistema de conversão de energia eólica. A partir dos ganhos do controlador PI é projetado o controlador fuzzy PI autoajustavel com o objetivo de melhorar a resposta em regime permanente da potencia controlada. A potencia gerada pelo gerador de relutancia variavel é injetada à rede eletrica, atraves do controle independente das potencias ativa e reativa, para este proposito é utilizado um conversor trifasico de dois níveis. Na parte experimental deste trabalho foi implementado o controle de corrente por histerese para maquina operando no modo motor, posteriormente foi implementado o controle de corrente e controle da tens~ao no barramento CC para a máquina operando no modo gerador. Os resultados de simulação e experimentais se mostraram coerentes validando os controladores propostos.
This work presents the direct power control of the switched reluctance generator of 12/8 using the self-tuning fuzzy PI controller and the vector control for inverter connected to the grid. Initially, the machine's operating principles and the topology of the power electronics converter used to drive this machine are studied. The model of switched reluctance machine is implemented in Matlab/Simulink simulation software using the characteristic curves of current and torque extracted using experimental data. Using the machine's model, It is designed the speed controller for its operation in motor mode. Also, the PI controller is designed for the power control loop based on the estimation of the wind energy conversion system. Using the gains of the PI controller, It is designed the self-tuning fuzzy PI controller, in order to improve the steady state response of the power control loop. The power generated by the switched reluctance generator is injected into the power grid through the independent control of active and reactive power, for this purpose is used a three-phase two level converter. In the experimental part of this work was implemented the hysteresis current control for machine operating in motor mode, also, It was implemented the current and DC bus voltage control for the machine operating in generator mode. The simulation and experimental results were proved consistent and these results validate the proposed controllers.
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Smart, Sean Christopher. "NMR examinations of control and ischemic rodent brain tissue." Thesis, Queen Mary, University of London, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.309450.
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Haga, Kristin Kerr. "The combined application of 'H MRI and '19F MRS to the study of cerebroprotection." Thesis, University of London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.312006.
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Steger, Ronny. "Einfluss einer MRT-Untersuchung auf die Funktionsstabilität nicht MRT-fähiger Herzschrittmacher und ICD." Doctoral thesis, Universitätsbibliothek Leipzig, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-144013.
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Die bildgebende Diagnostik im Magnetresonanztomographen ist für Träger implantierter, nicht MR-fähiger Herzschrittmacher und Cardioverter/Defibrillatoren potentiell risikoreich. Durch das starke externe Magnetfeld und die elektromagnetischen Signale des MRT-Gerätes können die antibradykarden und –tachykarden Therapiesysteme in ihrer korrekten Funktion erheblich gestört und durch die Antennenwirkung der Sonden myokardiale Schädigungen hervorgerufen werden.
In der vorliegenden Arbeit sind bei Trägern derartiger Implantate deren wichtigste Funktionsparameter vor und nach einer jeweiligen Untersuchung im MRT telemetrisch ermittelt worden. Anhand der statistischen Auswertung der prä- und postprozedualen Messwerte für Wahrnehmung (Sensing), Reizschwelle und Elektrodenimpedanz wurde der Einfluss einer MRT-Untersuchung auf die regelrechte Funktion der Herzschrittmacher- und ICD-Aggregate untersucht. Ein weiteres Augenmerk galt im Allgemeinen der grundsätzlichen Durchführbarkeit des Verfahrens und eventuellen Komplikationen hinsichtlich unzureichender Patientensicherheit.
Zum einen konnte gezeigt werden, dass nach sorgfältiger Abwägung von Risiko und Nutzen der Untersuchung, sowie entsprechenden Sicherheitsvorkehrungen, die MRT komplikationslos durchführbar ist. Weiterhin konnte keine Beeinträchtigung der regelrechten Funktion der Aggregate nachgewiesen werden.
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Craig-Craven, Alexander. "Development of Transmit and Receive Coils for 1H MRI/MRS on a 7T MR Scanner." Thesis, Norwegian University of Science and Technology, Department of Engineering Cybernetics, 2010. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-10930.
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High quality images with strong contrast, good resolution and geometrical consistency are of crucial importance in magnetic resonance imaging, where the relatively low intrinsic sensitivity of MR methods places high demands on the imaging hardware. One of many key components in the imaging system is the radiofrequency coil, responsible for transmitting excitation signals and/or listening for response from the object. In this project a number of such coils are developed for specific applications (namely proton imaging of rat and fish brains), then evaluated against phantoms and empirically in simulated imaging situations. Evaluation of the produced coils shows promising initial results, with various opportunities for further refinement into a device suitable for regular use.
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Anderson, Christian Edwin. "High-Field Magnetic Resonance Fingerprinting for Molecular MRI." Case Western Reserve University School of Graduate Studies / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=case152478492457623.
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Elschner, Cindy. "Analyse der knöchernen Einheilung von Biomaterialien mit der Magnetresonanztomographie." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-204714.
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Die Analyse von Implantat-Gewebe-Wechselwirkungen basiert derzeit hauptsächlich auf histologischen Techniken. Der invasive Charakter der histologischen Präparation lässt allerdings keine Untersuchung am lebenden Tier zu. Dadurch ist es nicht möglich, den Prozess der Implantateinheilung wiederholt an einem Tier zu beobachten. Die Folgen sind eine hohe Anzahl aufzuwendender Versuchstiere und eine Vergrößerung der Messunsicherheit infolge der gestiegenen biologischen Variabilität. Nicht-invasive, bildgebende Verfahren spielen daher eine zunehmende Rolle für die Entwicklung neuer Biomaterialien. Während die Computertomographie (CT) häufig zur Untersuchung der knöchernen Implantateinheilung verwendet wird, hat sich die Nutzung der Magnetresonanztomographie (MRT) für diese Fragestellungen bisher nicht etabliert. Bei der Magnetresonanztomographie handelt es sich, analog zur Computertomographie, um ein bildgebendes Verfahren zur nicht-invasiven Erzeugung digitaler Schnittbilder. Im Gegensatz zur CT, die das Hartgewebe abbildet, wird bei der MRT das Weichgewebe detektiert, wobei keine ionisierende Strahlung verwendet wird. Der große Vorteil der MRT gegenüber anderen bildgebenden Methoden besteht darin, dass es möglich ist, das Weichgewebe auf den Schnittbildern anhand verschiedener Kontraste darzustellen. Zusätzlich können MR-spezifische Parameter quantifiziert werden, die einen direkten Rückschluss auf die Struktur zulassen. Mit diesen Kennzahlen ist es möglich, Veränderungen im Weichgewebe analysieren. Das Ziel der Arbeit war es deshalb, die Eignung und mögliche Anwendungen der Magnetresonanzto-mographie (MRT) zur Analyse der Implantat-Gewebe-Wechselwirkungen zu erörtern. Für die Untersu-chungen wurde ein NMR-Spektrometer inklusive Imaging-Zubehör verwendet. Die Dissertationsarbeit beinhaltete sowohl die Untersuchung verschiedener Materialsysteme hinsichtlich ihrer Eignung für die MRT und deren Biokompatibilität, als auch die Analyse der knöchernen Einheilung ausgewählter Biomaterialien. Diese umfasste Aussagen zur Darstellbarkeit und Abgrenzbarkeit von Strukturen und beinhaltete auch quantitativ gewonnene Messparameter. Die Ergebnisse wurden stets im Vergleich mit der Histologie diskutiert. In der Arbeit konnte dargestellt werden, dass die Überprüfung der Eignung des zu untersuchenden Materials für die MRT vor der Analytik erfolgen muss. Es wurde demonstriert, dass Metalle erheblich mit dem MR-System wechselwirken können, was in der Konsequenz zu drastischen Störungen der Bildqualität führt. Diese Effekte waren stark von den ausgewählten Messparametern abhängig. Als ein MRT-geeignetes Verbundmaterial wurde Titan-beschichtetes Polyetheretherketon (PEEK/Ti) vorgeschlagen. Die Beschichtung mit Titan führte zu einer signifikant verbesserten Biokompatibilität des Kunststoffes. Die erfolgreiche Analyse der knöchernen Einheilung mit der Magnetresonanztomographie wurde im Rahmen von zwei tierexperimentellen Studien an verschiedenen Biomaterialien gezeigt (die Analyse erfolg-te ex vivo). Die Untersuchung der knöchernen Integration eines Zahnimplantates aus PEEK/Ti hatte das Ziel, die Darstellbarkeit des Implantates und knöcherner Strukturen mit der Magnetresonanztomographie zu evaluieren. Außerdem wurde ebenfalls gezeigt, dass es anhand der MRT-Schnittbilder möglich ist, quantitative Messgrößen zur Beschreibung des Einheilprozesses zu gewinnen. Aufgrund der geringen Versuchstierzahl wurde jedoch eine breite Streuung der Messdaten festgestellt. Allerdings besitzt die Studie durch die Untersuchung eines Zahnimplantates aus Polyetheretherketon/Titan mit der MRT nicht nur Neuheitswert in der Biomaterialforschung, sondern schlägt gleichzeitig eine Brücke zur klinischen, dentalen Implantologie. Die Bewertung der Darstellbarkeit knöcherner Strukturen und der verwendeten (teils tissue-engineerten) Knochenersatzmaterialien mit MRT und Histologie und des klinischen Erfolges derselben bildeten einen Schwerpunkt der zweiten tierexperimentellen Studie (die Analyse erfolgte ex vivo). Es war möglich, mit beiden bildgebenden Verfahren zu zeigen, dass sich die verwendeten Knochenersatzmaterialien nicht für die vorgesehene Anwendung eigneten. Die Beurteilung der Übereinstimmung der quantitativ gewonnenen Parameter beider Analysenmethoden bildete den Abschluss der Arbeit. Es wurde festgestellt, dass zwischen den Messdaten stets ein syste-matischer Unterschied bestand. Nachweislich war dieser aber weniger das Resultat der ungleichen lateralen Auflösungen oder der unterschiedlichen Darstellbarkeit von Gewebestrukturen der beiden Verfahren, sondern konnte auf den Einfluss der Analyse verschiedener Schichtebenen und individueller Unterschiede bei der digitalen Quantifizierung der auswertenden Personen zurückgeführt werdenCurrently, histological techniques are used to analyse implant-tissue-interactions. However, these methods are destructive and do not allow for the investigation of living animals. Therefore, it is not possible to study the integration of biomaterials repeatedly with one animal, resulting in a large number of animals and an increase of biological variability. Non-invasive imaging techniques have gained interest in the field of biomaterials. Whereas Computed Tomography (CT) was often used to evaluate the osseous integration, the assessment using Magnetic Resonance Imaging (MRI) has not been established, yet. MRI is a non-invasive medical imaging method that detects soft tissue. In contrast to CT the method does not require individuals to be exposed to radiation. The most important benefit of MRI is the possibility to acquire different soft tissue contrasts in situ because the various tissues have different signal intensities on MR images that can be altered by using different experimental parameters. Furthermore, it is possible to gain MR-specific properties that allow conclusions to the tissue structure. Thus, the objective of the doctoral thesis has been to investigate the suitability of MRI for the use in biometerial research and to show potential areas of application. The examinations were performed using a laboratory NMR-spectrometer inclusive imaging accessory. The thesis included an evaluation of the MR compatibility of different materials and their biocompati-bility and an analysis of the ingrowth of chosen biomaterials into bone. For that, the detection and identification of tissue structures and biomaterials was investigated with both, MRI and histology. Additionally, quantitative parameters were acquired and their comparability was assessed. It was clearly demonstrated, that metals interacted with the MR system and provoked large image distortions. These effects were strongly dependent on experimental parameters chosen. Polyetheretherketone with titanium coating (PEEK/Ti) was investigated and has been found to be MR safe. Above all, it was demonstrated that the biocompatibility of the polymer was significantly enhanced by coating with titanium. Within two animal studies the successful analysis of the osseous healing of different biomaterials with MRI was presented. To demonstrate the visibility of bony structures and biomaterials a dental implant made of PEEK/Ti was analysed. The ability to measure quantitative data in analogy to histomorphometry was shown, ditto. A large variation of the values was detected due to the limited number of animals used for the pilot study. Evaluating the displayability of bone and (to some extent tissue engineered) bone substitutes and assessing the clinical success of these materials was one main focus of the second animal study. Both, MRI and histological analysis could undeniably illustrate that all of the bone substitutes were not suitable for the chosen application. The thesis was completed with the determination of the agreement of quantitative values from both analysing methods. It was concluded that all values gained from the animal study were significantly different. It was proven that the chosen slice position and the image interpretation with two evaluators had a larger share to disagreement than the different lateral resolution of MRI and histological images or the diverging displayability of bone and bone substitutes. By investigating a MR suitable dental PEEK implant the doctoral thesis fulfils the criteria of novelty in biomaterial research. Moreover, it forges links between preclinical research and dental implantology
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Hu, Ruomin [Verfasser], and Lothar [Akademischer Betreuer] Schad. "Exploring Quadrupolar Interactions of 23Na and 35Cl with Triple-Quantum MRS/MRI / Ruomin Hu ; Betreuer: Lothar Schad." Heidelberg : Universitätsbibliothek Heidelberg, 2020. http://d-nb.info/1206416726/34.
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Williams, Rebecca Elizabeth. "Biochemical and neurotoxicological effects of L-2-chloropropionic acid on the brain : an MRS and MRI study." Thesis, University of Nottingham, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.243458.
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Hu, Ruomin [Verfasser], and Lothar R. [Akademischer Betreuer] Schad. "Exploring Quadrupolar Interactions of 23Na and 35Cl with Triple-Quantum MRS/MRI / Ruomin Hu ; Betreuer: Lothar Schad." Heidelberg : Universitätsbibliothek Heidelberg, 2020. http://nbn-resolving.de/urn:nbn:de:bsz:16-heidok-281022.
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Ermisch, Jörg. "Die fetale Hirnentwicklung zwischen der 16. -und 30. Schwangerschaftswoche- Eine postmortale Untersuchung von 117 Feten am 3Tesla- MRT." Doctoral thesis, Universitätsbibliothek Leipzig, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-115179.
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Für die Beurteilung der Hirnentwicklung erfolgte eine postmortale MRT- Untersuchung von totgeborenen Kindern im Rahmen einer virtuellen Autopsie.
Besondere Berücksichtigung innerhalb dieses Datenmaterials fand die Oberflächenveränderung im Sinne der Entstehung von Gyri und Sulci. Weiterhin wurde geprüft, wie sich die morphologische Entwicklung und damit die Germination und Migration der Nervenzellen in diesem Schwangerschaftszeitraum in der MRT darstellen und beurteilen lässt.
Im Ergebnis der Untersuchung zur Germination und Migration war vor allem zwischen der 18. und 25. SSW die zonale Gliederung des Hirnmantels mit “ventricular zone“, “intermediate zone“, “subplate zone“ und “cortical plate“ durch wechselnde Hypo –bzw. Hyperintensitäten in der MRT gut zu beurteilen.
Der zeitlich geordnete Ablauf in der Entstehung einzelner Sulci konnte in dieser Arbeit unter anderem auch mittels eines atlasartigen Teils abgebildet werden.
Dabei zeigte sich eine häufig etwas frühere Darstellbarkeit einzelner Sulci im postmortalen MRT im Vergleich zu den Studien an pränatalen MRT´s bei Schwangeren. Eine Streubreite des Auftretens der einzelnen Sulci von 2-3 Wochen bei gesunden Feten ist dabei zu berücksichtigen.
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Huber, Laurentius. "Mapping Human Brain Activity by Functional Magnetic Resonance Imaging of Blood Volume." Doctoral thesis, Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-165252.
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This dissertation describes the development, implementation, validation, optimization, and application, of a noninvasive and quantitative method for measuring cerebral blood volume changes with functional magnetic resonance imaging (fMRI) for mapping of neural activity changes.
Since its inception over twenty years ago, the field of fMRI has grown in usage, sophistication, range of applications, and impact. Nevertheless it has yet to exploit its full potential regarding, spatiotemporal resolution, signal specificity, and quantifiability of hemodynamic changes. By utilization of a new MR pulse sequence, new concepts of radio frequency pulses, and high magnetic fields (7 T), a novel fMRI method named SS-SI VASO is presented here that overcomes sensitivity limitations of other noninvasive quantitative imaging methods. In order to validate that its signal represents changes in cerebral blood volume without other contaminations, SS-SI VASO is implemented in animal models for a close comparison with established, but invasive methods. A good agreement of blood volume sensitivity has been found with the new method compared to the established ones. After its validation, the SS-SI VASO method and its unprecedented sensitivity was used to localize and quantify hemodynamic changes in applications where conventional oxygenation based fMRI methods are limited. (A) SS-SI VASO was used to investigate biophysical aspects of actively controlled arteries and passive balloon-like veins during activity induced hemodynamic changes. (B) SS-SI VASO was used to provide insights whether the interplay of neural activity and resultant vascular response are the same for tasks that increase neural activity compared to tasks that suppress neural activity. (C) SS-SI VASO was used to calibrate conventional oxygenation based fMRI to quantify local changes in oxygen metabolism. (D) The high sensitivity of SS-SI VASO was further used to obtain sub-millimeter resolutions and estimate activity changes between cortical layers. This enables to address questions not only where the brain is activated but also how and whereby this activity is evoked. The implementation and application of this new SS-SI VASO fMRI method is a major step forward for the field of imaging neuroscience; it demonstrates that the current limitations of fMRI can be even overcome with respect to quantifiability, spatial specificity and distinguishing between vascular and neuronal phenomena.
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Yan, Jiun-Lin. "Characterising peritumoural progression of glioblastoma using multimodal MRI." Thesis, University of Cambridge, 2017. https://www.repository.cam.ac.uk/handle/1810/267740.
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Glioblastoma is a highly malignant tumor which mostly recurs locally around the resected contrast enhancement. However, it is difficult to identify tumor invasiveness pre-surgically, especially in non-enhancing areas. Thus, the aim of this thesis was to utilize multimodal MR technique to identify and characterize the peritumoral progression zone that eventually leads to tumor progression. Patients with newly diagnosed cerebral glioblastoma were included consecutively from our cohort between 2010 and2014. The presurgical MRI sequences included volumetric T1-weighted with contrast, FLAIR, T2-weighted, diffusion-weighted imaging, diffusion tensor and perfusion MR imaging. Postsurgical and follow-up MRI included structural and ADC images. Image deformation, caused by disease nature and surgical procedure, renders routine coregistration methods inadequate for MRIs comparison between different time points. Therefore, a two-staged non-linear semi-automatic coregistration method was developed from the modification of the linear FLIRT and non-linear FNIRT functions in FMRIB’s Software Library (FSL). Utilising the above mentioned coregistration method, a volumetric study was conducted to analyse the extent of resection based on different MR techniques, including T1 weighted with contrast, FLAIR and DTI measures of isotropy (DTI-p) and anisotropy (DTI-q). The results showed that patients can have a better clinical outcome with a larger resection of the abnormal DTI q areas. Further study of the imaging characteristics of abnormal peritumoural DTI-q areas, using MRS and DCS-MRI, showed a higher Choline/NAA ratio (p = 0.035), especially higher Choline (p = 0.022), in these areas when compared to normal DTI-q areas. This was indicative of tumour activity in the peritumoural abnormal DTI-q areas. The peritumoural progression areas were found to have distinct imaging characteristics. In these progression areas, compared to non-progression areas within a 10 mm border around the contrast enhancing lesion, there was higher signal intensity in FLAIR (p = 0.02), and T1C (p < 0.001), and there were lower intensity in ADC (p = 0.029) and DTI-p (p < 0.001). Further applying radiomics features showed that 35 first order features and 77 second order features were significantly different between progression and non-progression areas. By using supervised convolutional neural network, there was an overall accuracy of 92.4% in the training set (n = 37) and 78.5% in the validation set (n=14). In summary, multimodal MR imaging, particularly diffusion tensor imaging, can demonstrate distinct characteristics in areas of potential progression on preoperative MRI, which can be considered potential targets for treatment. Further application of radiomics and machine learning can be potentially useful when identifying the tumor invasive margin before the surgery.
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Pierre, Eric Y. "Reliable Use of Acquired and Simulated Signal Databases to Reduce MRI Acquisition Time." Case Western Reserve University School of Graduate Studies / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=case1404220001.
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Leclair, Nadine Stéfanie. "Diffusionsgewichtete Ganzkörper-MR-Bildgebung bei Kindern mit Chronischer Rekurrierender Multifokaler Osteomyelitis." Doctoral thesis, Universitätsbibliothek Leipzig, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-218109.
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Zielsetzung: Die Chronisch-Rekurrierende Multifokale Osteomyelitis/Chronische Nicht-bakterielle
Osteitis (CRMO/CNO) ist eine seltene auto-inflammatorische Erkrankung, deren typische Symptome
starke Knochenschmerzen und lokale Schwellungen sind. Da die Ursachen muskuloskelettaler
Beschwerden bei Kindern und Heranwachsenden vielfältig sein können, ist die
differentialdiagnostische Unterscheidung einer CRMO/CNO von anderen Erkrankungen,
unspezifischen Schmerzen oder einer malignen Grunderkrankung als Quelle der Symptome schwierig.
Neue Techniken wie die diffusionsgewichtete Bildgebung (DWI) in der Magnetresonanztomographie
(MRT) erlauben Rückschlüsse auf die Gewebestruktur und können in bestimmten Fällen eine
Unterscheidung zwischen entzündlichen und malignen Prozessen vereinfachen. Ziel dieser Studie war
es daher, die Sichtbarkeit von CRMO-/CNO-Läsionen mittels der DWI-Ganzkörperbildgebung zu
evaluieren und den potentiellen klinischen Wert zu untersuchen.
Material und Methoden: Sechzehn Patienten mit bekannter CRMO/CNO wurden bei 3 Tesla
untersucht. Das Untersuchungsprotokoll beinhaltete u. a. 2D Short Tau Inversion Recovery (STIR)
und diffusionsgewichtete Sequenzen in axialer Schichtführung. Die Sichtbarkeit von Läsionen in der
DWI und der STIR wurde von 2 Auswertern im Konsensus evaluiert. Für alle Läsionen und in der
korrespondierenden Referenzlokalisation wurden der Apparent Diffusion Coefficient (ADC) ermittelt.
Ergebnisse: Insgesamt wurden 33 Läsionen eingeschlossen (durchschnittlich 2 Läsionen pro Patient),
die sowohl in der STIR als auch in der DWI sichtbar waren. Diese waren vornehmlich in den langen
Röhrenknochen lokalisiert. Der mittlere ADC-Wert in Läsionen betrug 1283 mm2/s und war somit
signifikant höher als in der Referenzregion, hier betrug der mittlere ADC 782 mm2/s. Im ADCVerhältnis
(Läsion vs. Referenzregion) zeigten 82 % der Läsionen eine relative
Signalintensitätssteigerung um mehr als 10 %, und 76 % (25 Läsionen) zeigten eine
Intensitätssteigerung von mehr als 15 %. Der mittlere relative Signalintensitätsanstieg betrug 69 %.
Schlussfolgerung: Diese Studie zeigt, dass die diffusionsgewichtete Ganzkörperbildgebung bei 3 Tesla
zuverlässig bei Kindern durchgeführt werden kann. Die ADC-Werte waren in CRMO-/CNO-Läsionen
im Vergleich zur Referenzregion signifikant erhöht. Daher wird die Ganzkörperbildgebung in
Kombination mit klinischen Angaben von uns als vielversprechende Methode angesehen, um benigne
inflammatorische Prozesse anhand der ADC-Werte von bestimmten Malignitäten zu unterscheiden.
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Ccantuta, Chirapo Karlos Alexander. "Controle de potência do gerador de relutância variável de 12/8 utilizando o controlador fuzzy pi auto-ajustável." reponame:Repositório Institucional da UFABC, 2018.
Find full textAbstract:
Orientador: Prof. Dr. José Luis Azcue PumaCoorientador: Prof. Dr. José Alberto Torrico Altuna
Dissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Engenharia Elétrica, Santo André, 2018.
Este trabalho apresenta o controle de potência do gerador de relutância variável de 12/8 utilizando o controlador Fuzzy PI auto-ajustável e o controlador P+ressonante para o conversor conectado à rede elétrica. Inicialmente são estudados os princípios de operação da máquina e a topologia do conversor eletrônico de potência. Usando o software de simulação Matlab/Simulink é implementado o modelo da máquina de relutância variável utilizando as curvas características de corrente e de torque. Com o objetivo de controlar a potência gerada pela máquina e utilizando seu modelo matemático dinâmico projeta-se o controlador PI, e implementa-se o controlador Fuzzy PI auto-ajustável para atingir o mesmo objetivo. Assim, projeta-se também um controlador PI para o controle da tensão CC além de um controlador P+ressonante com o objetivo de melhorar a resposta em regime permanente da potência injetada na rede elétrica. Para este propósito é utilizado um conversor monofásico de dois níveis. Os resultados das simulações mostram o bom desempenho do sistema proposto e o controlador de potência é validado também através de resultados experimentais.
This work presents the power control of the 12/8 variable reluctance generator using Fuzzy self-tuning PI controller and the P+resonant controller for the converter connected to the electric network. Initially are studied the principles of operation of the machine and power electronic converter topology. Using the Matlab/Simulink simulation software is implemented the model of switched reluctance machine using the current and its torque characteristic curves. With the purpose of controlling the power generated by the machine and using his dynamic mathematical model is designed the PI controller, and the Fuzzy self-tuning PI controller is implemented to achieve the same objective. So, also is designed a PI controller for control of the link DC, in addition to the P+resonant controller with the objective of improving the response to its steady state of the injected power into the electric network. For this purpose it is used a single-phase two-level converter. The results of the simulations show the good performance of the proposed system and the power controller is validated by experimental results.
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Nguyen, Thanh Thao [Verfasser], and Irina [Akademischer Betreuer] Mader. "Functional MRI and DTI fiber tracking in patients with gliomas = Funktionelle MRT und DTI Fiber Tracking bei Patienten mit Gliomen." Freiburg : Universität, 2011. http://d-nb.info/1123461236/34.
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Kleimaier, Dennis [Verfasser], and Lothar [Akademischer Betreuer] Schad. "Exploring Protein Interactions with 23Na Triple-quantum MRS and 1H Chemical Exchange Saturation Transfer MRI / Dennis Kleimaier ; Betreuer: Lothar Schad." Heidelberg : Universitätsbibliothek Heidelberg, 2021. http://d-nb.info/1227155832/34.
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Kleimaier, Dennis [Verfasser], and Lothar R. [Akademischer Betreuer] Schad. "Exploring Protein Interactions with 23Na Triple-quantum MRS and 1H Chemical Exchange Saturation Transfer MRI / Dennis Kleimaier ; Betreuer: Lothar Schad." Heidelberg : Universitätsbibliothek Heidelberg, 2021. http://nbn-resolving.de/urn:nbn:de:bsz:16-heidok-293608.
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Dhital, Bibek. "Characterizing Brain White Matter with Diffusion-Weighted Magnetic Resonance." Doctoral thesis, Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-180140.
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It has been known for almost two decades that the water proton NMR signal of diffusing water molecules in brain white matter undergoes a non-monoexponential decay with increasing diffusion gradient factor b. With the help of numerical simulations and analytical expressions, much effort has been directed to describing the signal decay and to extracting relevant biophysical features of the system under investigation. However, the physical basis of such nonmonoexponential behavior is still not properly understood.
The primary difficulty in characterizing this phenomenon is the variation in behavior in the different directions of diffusion measurement. A combined framework that accounts for the diffusion process in all directions requires several parameters. Addition of many such parameters renders a model to be unwieldy and over-complicated, but over-simplifications can be shown to miss crucially relevant information in the data.
In this thesis, I have attempted to handle this problem with simple measurements that span a wide range of parameter space. Compared to often-performed measurements that probe diffusion over a time-scale of 50-100 ms with relatively low diffusion weighting, the measurements here have been done for very short diffusion times of 2 ms and also very long diffusion times up to 2 s. The temperature dependence of the diffusion coefficients has also been extensively probed. To avoid problems related to gross tissue heterogeneity, diffusion-weighted MR imaging in vivo was performed with ultra-high resolution. These simple measurements allowed sequential assessment of many possible arguments that could have led to such non-monoexponential decay curves. Finally, it was concluded that the water in the glial processes was the major contributor to the non-exponential decay, giving rise to a \'slow\' component both along the axonal fibers and transverse to them.
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Peterson, Erika. "Synthetic MRI for visualization of quantitative MRI." Thesis, Linköpings universitet, Avdelningen för radiologiska vetenskaper, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-102651.
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Magnetic resonance imaging (MRI) is an imaging technique that is used in hospitals worldwide. The images are acquired through the use of an MRI scanner and the clinical information is provided through the image contrast, which is based on the magnetic properties in biological tissue. By altering the scanner settings, images with different contrast properties can be obtained. Conventional MRI is a qualitative imaging technique and no absolute measurements are performed. At Center for Medical Imaging and Visualization (CMIV) researchers are developing a new MRI technique named synthetic MRI (SyMRI). SyMRI is based on quantitative measurements of data and absolute values of the magnetic properties of the biological tissue can be obtained. The purpose of this master thesis has been to take the development of SyMRI a step further by developing and implementing a visualization studio for SyMRI imaging of the human brain. The software, SyMRI Brain Studio, is intended to be used in clinical routine. Input from radiologists was used to evaluate the imaging technique and the software. Additionally, the requirements of the radiologists were converted into technical specifications for the imaging technique and SyMRI Brain Studio. Additionally, validation of the potential in terms of replacing conventional MRI with SyMRI Brain Studio was performed. The work resulted in visualization software that provides a solid formation for the future development of SyMRI Brain Studio into a clinical tool that can be used for validation and research purposes. A list of suggestions for the future developments is also presented. Future clinical evaluation, technical improvements and research are required in order to estimate the potential of SyMRI and to introduce the technique as a generally used clinical tool.
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Kotowski, Susan E. "Understanding a Low Back Pain Pathway: Utilizing MRI and MRS to Link Pain Due to Muscle Inflammation to Changes in Brain Metabolites." University of Cincinnati / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1243367529.
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Mirus, Matthew M., Sergey V. Tokalov, Gerald Wolf, Jerilyn Heinold, V. Prochnow, and Nasreddin Abolmaali. "Noninvasive assessment and quantification of tumour vascularisation using MRI and CT in a tumour model with modifiable angiogenesis – An animal experimental prospective cohort study." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2018. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-232305.
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Background
To investigate vascular-related pathophysiological characteristics of two human lung cancers with modifiable vascularisation using MRI and CT.
Methods
Tumour xenografts with modifiable vascularisation were established in 71 rats (approval by the Animal Care Committee was obtained) by subcutaneous transplantation of two human non-small-cell lung cancer (NSCLC) cells (A549, H1299) either alone or co-transplanted with vascular growth promoters. The vascularity of the tumours was assessed noninvasively by MRI diffusion-weighted-imaging (DWI), T2-weighted, and time-of-flight (TOF) sequences) as well as contrast-enhanced CT (CE-CT), using clinical scanners. As a reference standard, histological examinations (CD-31, fluorescent beads) were done after explantation.
Results
Microvessel density (MVD) was higher in co-transplanted tumours (171 ± 19 number/mm2) than in non-co-transplanted tumours (111 ± 11 number/mm2; p = 0.002). Co-transplanted tumours showed higher growth rates and larger tumour vessels at TOF-MRI as well as larger necrotic areas at CE-CT. In co-transplanted tumours, DWI revealed higher cellularity (lower minimal ADCdiff 166 ± 15 versus 346 ± 27 mm2/s × 10−6; p < 0.001), highly necrotic areas (higher maximal ADCdiff 1695 ± 65 versus 1320 ± 59 mm2/s × 10−6; p < 0.001), and better-perfused tumour stroma (higher ADCperf 723 ± 36 versus 636 ± 51 mm2/s × 10−6; p = 0.005). Significant correlations were found using qualitative and quantitative parameters: maximal ADCperf and MVD (r = 0.326); maximal ADCdiff and relative necrotic volume on CE-CT (r = 0.551); minimal ADCdiff and MVD (r = −0.395).
Conclusions
Pathophysiological differences related to vascular supply in two human lung cancer cell lines with modifiable vascularity are quantifiable with clinical imaging techniques. Imaging parameters of vascularisation correlated with the results of histology. DWI was able to characterise both the extent of necrosis and the level of perfusion.
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Jiang, Yun. "DEVELOPMENT OF NOVEL PULSE SEQUENCES FOR MAGNETIC RESONANCE FINGERPRINTING." Case Western Reserve University School of Graduate Studies / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=case1480691677961147.
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Fromme, Vivian. "Computertomographische und magnetresonanztomographische Anatomie der Speicheldrüsen der Katze." Doctoral thesis, Universitätsbibliothek Leipzig, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-224710.
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Zielstellung: Die Verwendung von Computertomographie und Magnetresonanzto-mographie zur Diagnostik von pathologischen Weichteilveränderungen, wie Läsionen der Speicheldrüsen, wird empfohlen. Diese begründet sich in Ihrer hohen Bildauflö-sung und dem guten Bildkontrast. Nach unserem Wissen gibt es aktuell keine publi-zierte Literatur, welche sich mit der CT- oder MRT-Anatomie der Speicheldrüsen der Katze beschäftigt. Ziel der vorliegenden Arbeit war es daher, Schnittbildmerkmale der Speicheldrüsen zu definieren und Landmarken für eine sichere Identifikation zu be-schreiben. Material und Methoden: Es wurden zwei Gruppen von Katzen untersucht. Die pros-pektiv untersuchten Tiere bestanden aus 16 Katzen, welche aus Gründen euthana-siert wurden, die nicht in Zusammenhang mit der Studie standen. Diese erfuhren ein CT (1 mm Schichtdicke) und 0,5 Tesla MRT (T2W, T2W SPIR, PDW, T1W) des Kop-fes. Im retrospektiven Anteil der Studie wurden CT-Untersuchungen (0,8-1 mm Schichtdicke) von 25 Katzen und MRT-Untersuchungen (T2W, T1W vor und nach Kontrastmittelgabe) von 21 Katzen verwendet. Diese Untersuchungen wurden zwi-schen 2005 und 2013 in unserer Klinik angefertigt. Dabei konnten keine Pathologien in Zusammenhang mit den Speicheldrüsen festgestellt werden. Alle Speicheldrüsen wurden bezüglich Identifizierbarkeit, Abgrenzbarkeit, Größe und Signalverhalten un-tersucht. Wenn vorhanden, wurden anatomische Landmarken die Speicheldrüsen umgebend notiert. Zusammenfassung 80 Ergebnisse: 94,3% der Glandulae parotidae, 90,7% der Glandulae mandibulares und 96,8% der Glandulae zygomaticae konnten mit dem CT identifiziert werden. Beim MRT waren es 94,1% der Glandulae parotidae, 99,2 % der Glandulae mandibulares, 88,9% der Glandulae zygomaticae und 51,4 % der Glandulae buccalis ventralis. In beiden Gruppen konnten keine der restlichen kleinen Speicheldrüsen identifiziert werden, dies galt für beide Schnittbildverfahren. Als hilfreiche anatomi-sche Landmarken konnten der äußere Gehörgang, der M. masseter, der M. pterygo-ideus medialis und der Bulbus oculi herangezogen werden. Die medianen Dichtewer-te lagen für die Glandula parotis, die Glandula mandibularis und die Glandula zygo-matica bei 65 HU, 62 HU und 57 HU. Die Parotis war überwiegend dezent hyperin-tens zur Muskulatur und hypointens zum Fett. Die Mandibularis, Zygomatica, und Glandula buccalis ventralis stellten sich hauptsächlich hyperintens zur Muskulatur und hypointens zu Fettgewebe dar. Dieses Signalverhalten war für T1W, T2W und T2W SPIR (fettunterdrückt) gewichtete Sequenzen gleich. Die Größe war für beide Gruppen und Modalitäten vergleichbar und lag bei circa 17 x 6 mm (gemessen von lateral nach medial und von dorsal nach ventral) bei der Glandula parotis, 8 x 17 mm bei der Glandula mandibularis, 10 x 7 mm bei der Glandula zygomatica und bei der Glandula buccalis ventralis 3 x 10 mm. Schlussfolgerungen: Landmarken und Aussagen über die Signalintensität bezie-hungsweise Dichte und die Größe der Glandula parotis, Glandula mandibularis, Glandula zygomatica und der Glandula buccalis ventralis konnten erhoben werden. Die mangelhafte Identifizierbarkeit der restlichen kleinen Speicheldrüsen, im Ver-gleich zu den oben genannten, kann vor allem mit dem unzureichenden Weichteil-kontrast zum umliegenden Gewebe im CT und der niedrigen Auflösung des Nieder-feld-MRTs erklärt werden. Neuere MRT-Techniken können detailliertere Bilder er-zeugen und so eine Beschreibung der kleinen Speicheldrüsen ermöglichenObjective: Due to their high resolution and useful contrast resolution, CT and MRI are recommended methods for diagnosing pathological changes of soft tissues such as lesions of the salivary glands. To our knowledge, no studies about the CT or MR anatomy of the feline salivary glands have been published yet. The aim of the study was to define anatomical characteristics of the salivary glands in cross-sectional im-ages and to describe landmarks for a reliable identification. Materials and methods: Two groups of cats where examined. In a prospective trial, 16 cats, euthanized for reasons unrelated to the study, underwent a head CT (1 mm slice thickness) and 0.5 Tesla MRI scans (T2W, T2W SPIR, PDW, T1W). In a retro-spective trial, the CT scans (0.8-1 mm slice thickness) of 25 cats and the MR scans (T2W, T1W, pre- and post-contrast) of 21 cats were used. These scans were per-formed at our clinic between 2005 and 2013. No signs of salivary-gland-related pa-thologies were visible. All images were reviewed with respect to the following criteria: the presence, delineation and size of the salivary glands as well as the signal intensi-ty. Anatomical landmarks surrounding the glands were also recorded. Results: 94.3% of the parotid glands, 90.7% of the mandibular glands and 96.8% of the zygomatic glands could be delineated using CT. With MRI, 94.1% of the parotid Summary 82 glands, 99.2 % of the mandibular glands, 88.9% of the zygomatic glands and 51,4 % of the ventral buccal glands could be identified. In both groups the other small salivary glands could not be visualized neither in CT nor in MRI. Anatomical landmarks such as the external ear canal, the M. masseter, the M. pterygoideus medialis and the Bulbus oculi facilitate the identification. The mean density of the parotid gland, the mandibular gland and the zygomatic gland was 65 HU, 62 HU and 57 HU, respectively. The parotid gland was mainly modestly hyperintense to muscle and hypointense to fat. The mandibular, zygomatic and ven-tral buccal glands were hyperintense to muscle and hypointense to fat. Signal intensi-ties were similar for T1W, T2W and T2W SPIR images. Sizes were comparable for both groups and modalities and measured about 17x6 mm (lateral to medial and dor-sal to ventral) for the parotid gland, 8 x 17 mm for the mandibular gland, 10x7 mm for the zygomatic gland and 3x10 mm for the ventral buccal gland. Conclusions: Landmarks were recorded and data regarding the density/signal in-tensity and the size of the parotid gland, the mandibular gland, the zygomatic gland and the ventral buccal gland could be gathered. The discrepancy between depicting the small glands and the above mentioned glands can be explained mainly by the lack of contrast to the surrounding tissue in CT and the low spatial resolution in low-field MRI. Advanced MRI techniques are expected to produce more detailed images and therefore those techniques could be used to also describe the small salivary glands
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Lustig, Michael. "Sparse MRI /." May be available electronically:, 2008. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.
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Mccrea, Gavin. "Mrs Engels." Thesis, University of East Anglia, 2013. https://ueaeprints.uea.ac.uk/48694/.
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The creative component of the thesis consists of a novel entitled Mrs Engels. Mrs Engels is a first-person narrative from the perspective of Lizzie Burns, the Irish lover of the Communist leader Friedrich Engels. The action of the novel is focused on the years 1870-72 when Lizzie and Friedrich move from Manchester to London in order to be close to the Marx’s and the active international Communist scene there. The critical component consists of an essay entitled ‘Illusions of Truth’. ‘Illusions of Truth’ is a meditation on some of the questions raised when we speak of the category of ‘historical fiction’. It is a response to the fact that, often, discussions of historical fiction view ‘the past’ as textual and therefore to some degree unknowable, while taking for granted the knowability of ‘the present’. In other words, in order to assert the textuality of the past, many discussions of historical fiction juxtapose it to an immediately knowable present, sometimes called ‘direct’ or ‘present experience’. But is it true that the present is a more solid, knowable form of human experience than the past? Is direct engagement with reality even possible? Does the present exist at all, except as an historical fiction? The essay uses the theory of Michel Foucault, specifically his ‘archaeological’ and ‘genealogical’ approaches to history, as lenses through which to examine these questions. Grouping its analyses around the larger themes of time, space and truth, it considers whether anything in human experience can, in fact, be present and non-historical (and therefore entirely knowable and true). Can conscious human experience be anything other than historical and fictional? If indeed it cannot, is ‘historical fiction’ as a separate literary classification sustainable?
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Bonhorst, Nicole. "Temperaturveränderungen bei Säuglingen und Kleinkindern während einer 3T-MRT-Untersuchung in Sedierung." Doctoral thesis, Universitätsbibliothek Leipzig, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-77405.
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Bei einer MRT in Sedierung steht der potentielle Wärmeverlust über die Körperoberfläche einem Temperaturanstieg durch die Absorption von Energie aus dem Hochfrequenzfeld der Sendespule gegenüber. Bei Schädel-MRT-Untersuchungen in bereits vorliegenden Studien (1,5T, 3T) konnte mittels Ohrtemperaturmessung vor und nach der MRT ein Temperaturanstieg von 0,5 ° C bei Säuglingen und Kleinkindern gemessen werden. In der vorliegenden Arbeit sollte untersucht werden, ob bei 3T-MRT-Untersuchungen unterschiedlicher Körperregionen und Dauer in Propofol-Sedierung bei Säuglingen und Kleinkindern eine Zu- oder Abnahme der Körpertemperatur stattfi ndet und ob eine kontinuierliche Temperaturüberwachung auf der Haut eine verlässliche Messmethode ist. In der klinischen Observationsstudie wurden 50 Kinder im Alter bis zu 6 Jahren eingeschlossen und eine 3T-MRT in Propofol-Sedierung durchgeführt (ASA 1 und 2). Erstmalig erfolgte die Temperaturüberwachung kontinuierlich axillär mit einem Fiber TEMPTM Reusable Fiber-optic Surface Temperature Sensor (Invivo, Orlando/Florida, USA). Zur Kontrolle wurde die Ohrtemperatur vor und nach der MRT mit einem Infrarotthermometer First Temp Genius (Covidien Deutschland GmbH) gemessen und vegetative Reaktionen dokumentiert. Es zeigte sich ein mit der Literatur vergleichbarer signi fikanter mittlerer Temperaturanstieg auf der Haut von 36,4 ± 0,5 °C auf 36,9 ± 0,5 ° C auch bei unterschiedlichen Untersuchungszeiten und -regionen. Die nachgewiesene Erwärmung ist bei gesunden Kindern nur von geringer klinischer Relevanz. Es sind bei einer 3T-MRT-Untersuchung weder eine verstärkte Wärmezufuhr noch eine Kühlung notwendig, um Säuglinge und Kleinkinder normotherm zu halten. Ist bei speziellen Indikationen eine kontinuierliche Temperaturüberwachung notwendig, liefert ein faseroptischer Temperatursensor korrekte DatenIn case of MRI in infants and children during propofol sedation the potential loss of body temperature confronts the temperature increase due to the absorption of energy from the high-frequency field of the transmitter coil. Therefore the physician must be aware of both effects when caring for sedated children. Objective of the present study is the effect of 3T-MRI of different body regions and scan duration on body temperature measured continuously in propofol sedated infants and children, which was not performed previously. 50 children in the age up to 6 years have been included in the observational study carried out between October 2008 and March 2009 at the Department of Pediatric Radiology, University of Leipzig. They underwent an elective 3T-MRI while sedated with propofol. The temperature monitoring has been carried out continuously axillary with a new fiber-optic sensor. For control, the tympanic temperature has been measured prior and after the MRI-examination with an infrared thermometer. A significant (p<0,05) medial temperature increase from 36,4 ± 0,5 °C to 36,9 ± 0,5 °C was evident measured axillarly with the fiber-optic sensor. Heart rate and oxygen saturation were stable throughout the MRI scan. In healthy children, the measured increase of temperature during 3T-MRI is only of minor clinical relevance. If a continuous temperature monitoring is necessary in cases with special indications e.g. critical ill children, a fiber-optical temperature sensor generates reliable data
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Sünkel, Henning. "Prognostischer Wert der kardialen Magnetresonanztomographie bei Patienten mit ST-Hebungsinfarkt - Analyse der Parameter linksventrikuläre Ejektionsfraktion, Infarktgröße, mikrovaskuläre Obstruktion und myokardialer „Salvage“ in einer multizentrischen Studie." Doctoral thesis, Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-172834.
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Die kardiale Magnetresonanztomographie (MRT) ermöglicht nach einem akuten Myokardinfarkt (AMI) die Visualisierung und Quantifizierung der Myokardschädigung anhand verschiedener Parameter wie Ejektionsfraktion (EF), Infarktgröße, Mikrovaskuläre Obstruktion (MO) und „Myocardial Salvage Index“ (MSI). Anhand dieser MRT-Marker kann das Risiko für kardiovaskuläre Komplikationen eingeschätzt werden, was für die Weiterversorgung des Patienten sowie für die kardiologische Forschung von großem Interesse ist.
In dieser Arbeit wurde die prognostische Relevanz der MRT-Parameter erstmals in einer großen, multizentrischen Studie untersucht. Zudem sollte unter den vier genannten MRT-Markern derjenige mit der größten prognostischen Aussagekraft ermittelt werden. Dazu wurden 795 Patienten aus der AIDA STEMI Studie einer MRT unterzogen und dann zwölf Monate lang im Hinblick auf den kombinierten Endpunkt „Major Adverse Cardiac Events“ (MACE; bestehend aus Tod, Reinfarkt und Klinikaufnahme wegen Herzinsuffizienz) nachbeobachtet.
Die Ergebnisse belegen, dass die genannten MRT-Parameter prognostisch relevant sind und insbesondere die MO und die Infarktgröße einen Einfluss auf die Prognose ausüben, welcher über den Wert etablierter klinischer Risikomarker hinausgeht. Herausragende Bedeutung kommt dabei der MO zu, welche nach multivariater Analyse der potenteste MRT-Prädiktor für kardiovaskuläre Ereignisse ist.
Somit sollten die MRT-Parameter in kommenden kardiologischen Studien als Surrogatmarker für klinische Endpunkte berücksichtigt werden. Zudem könnten sie für den klinischen Alltag die Möglichkeit bieten, die Patientenversorgung enger an die individuelle Prognose anzupassen.
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Ellis, Lucy C. J. "Human and rat multidrug resistance-associated proteins (MRP/Mrp)." Thesis, University of Aberdeen, 2010. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=128325.
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The multidrug resistance associated proteins (MRP(human)Mrp (rat) are ATP-dependent transporters responsible for the efflux of a wide range of substrates, including endogenous compounds e.g. bilirubin, drug metabolites e.g. paracetamol glucuronide and fluorescent dyes e.g. 5 (and 6)-carboxy-2’,7’-dichlorofluorescein (CDF). Mrp1-6 (abccl-6) are expressed in rat liver, with Mrp2 being expressed at the highest level. Isolation of hepatocytes by in situ collagenase perfusion causes bile canalicular disruption and internalisation of Mrp2. Cells cultured in a sandwich configuration of Matrigel or collagen (Type 1) showed bile canalicular reformation at different days in cell culture, depending on the extracellular matrix and time of overlay. We have developed a method for quantifying Mrp-mediated efflux in hepatocytes cultured in a sandwich configuration of collagen (Type 1). This method is unique in its ability to distinguish between sinusoidal efflux, canalicular efflux and diffusion in intact hepatocytes. Alternative in vitro models of Mrp2-mediated efflux include the vesicular (direct and indirect methods) and the ATPase assays. We have used these assays to identify atorvastatin, fluvastatin, lovastatin, pitavastatin, pravastatin, rosuvastatin and simvastatin as substrates of human and rat MRP2/Mrp2. A close correlation was seen between the kinetic parameters of transport of the Mrp2 substrate; CDF determined in sandwich cultured rat hepatocytes using the method above (Km = 3.5 – 9.9 μM), vesicle preparations (Km = 37.9 μM) and membrane preparations (Km = 18.7 μM). We also present data to implicate the nuclear receptors, PXR, CAR and FXR in the regulation of abcc2 and abcc3 and PXR and CAR in abcc1 gene regulation. Abcc2 and abcc5 are also up-regulated in response to a toxic insult to the cell, probably via Nrf2 activation, suggesting a role in cell defence.
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Torkul, Orhan. "A comparison of MRP/GT and MRP/JS scheduling." Thesis, Cranfield University, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.333138.
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Ihme, Klas. "Functional and structural neuroimaging of facial emotion recognition in alexithymia." Doctoral thesis, Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-165971.
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Research in the last decades has shown that individuals with high degrees in the personality trait of alexithymia not only have difficulties in identifying and recognizing own feelings, but also show deficits in reading emotions from facial expressions of other people. Therefore, the current dissertation investigates the neural correlates of recognizing emotional facial expressions as a function of alexithymia. Initially, a theoretical introduction is given and existing findings from behavioral as well as structural and functional neuroimaging research are presented. Open questions are identified and addressed in one structural and two functional magnetic resonance imaging studies that were compiled into three original research articles. Study 1 examined the gray matter profile of high and low alexithymic individuals in selected brain regions relevant for processing emotional faces. In Study 2, functional neuroimaging was used to investigate the neural correlates of high alexithymic individuals\' difficulties in labeling briefly presented (≤ 100 ms) facial expressions of emotion. Study 3 investigated neural activations as a function of alexithymia during the labeling of emotional facial expressions when these are presented with little temporal constraints (≥ 1 s). The results of these studies are summarized and integrated with the existing literature. Finally, open issues are discussed and ideas for further research are outlined.
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Thomas-Seale, Lauren Elizabeth Jane. "Application of magnetic resonance elastography to atherosclerosis." Thesis, University of Edinburgh, 2015. http://hdl.handle.net/1842/21053.
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Atherosclerosis is the root cause of a wide range of cardiovascular diseases. Although it is a global arterial disease, some of the most severe consequences, heart attack and stroke, are caused by ischemia due to local plaque rupture. The risk of rupture is related to the mechanical properties of the plaque. Magnetic resonance elastography (MRE) images tissue elasticity by inverting, externally excited, harmonic wave displacement into a stiffness map, known as an elastogram. The aim of this thesis is to computationally and experimentally investigate the application of MRE to image the mechanical properties of atherosclerotic plaques. The cardiac cycle, lumen boundary, size and inhomogeneous nature of atherosclerotic plaques pose additional complications compared to more well-established MRE applications. Computational modelling allowed these complications to be assessed in a controlled and simplified environment, prior to experimental studies. Computational simulation of MRE was proposed by combining steady state shear waves, yielded by finite element analysis, with the 2D Helmholtz inversion algorithm. The accuracy and robustness of this technique was ascertained through models of homogeneous tissue. A computational sensitivity study was conducted through idealised atherosclerotic plaques, incorporating the effects of disease variables and mechanical, imaging and inversion parameters on the wave images and elastograms. Subject to parameter optimisation, a change in local plaque shear modulus with composition was established. Amongst other variables, an increase of the lipid pool volume in 10mm3 increments was shown to decrease the predicted shear modulus for stenosis sizes between 50% and 80%. The limitations of the Helmholtz inversion algorithm were demonstrated. A series of arterial phantoms containing plaques of various size and stiffness were developed to test the experimental feasibility of the technique. The lumen was identifiable in the wave images and elastograms. However the experimental wave propagation, noise and resolution left the vessel wall and plaque unresolvable. A computational replica of the phantoms yielded clearer wave images and elastograms, indicating that changes to the experimental procedure could lead to more successful results. The comparison also highlighted certain areas for improvement in the computational work. Imaging protocol for in vivo MRE through the peripheral arteries of healthy volunteers and peripheral artery disease patients was developed. The presence of physiological motion and low signal to noise ratios made the vessel anatomy unidentifiable. The application of MRE to atherosclerotic plaques through simulations, arterial phantoms, healthy volunteers and patients has shown that although there is the potential to identify a change in shear modulus with composition, the addition of realistic experimental complications are severely limiting to the technique. The gradual addition of complications throughout the thesis has allowed their impact to be assessed and in turn has highlighted areas for future research.
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Holiga, Štefan. "Personalizing functional Magnetic Resonance Protocols for Studying Neural Substrates of Motor Deficits in Parkinson’s Disease." Doctoral thesis, Universitätsbibliothek Leipzig, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-124904.
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Parkinson’s disease (PD) is a progressive neurodegenerative movement disorder characterized by a large number of motor and non-motor deficits, which significantly contribute to reduced quality of life. Despite the definition of the broad spectrum of clinical characteristics, mechanisms triggering illness, the nature of its progression and a character of therapeutic effects still remain unknown. The enormous advances in magnetic resonance imaging (MRI) in the last decades have significantly affected the research attempts to uncover the functional and structural abnormalities in PD and have helped to develop and monitor various treatment strategies, of which dopamine replacement strategies, mainly in form of levodopa, has been the gold standard since the late seventies and eighties. Motor, task-related functional MRI (fMRI) has been extensively used to assess the pathological state of the motor circuitry in PD. Several studies employed motor paradigms and fMRI to review the functional brain responses of participants to levodopa treatment. Interestingly, they provided conflicting results. Wide spectrum of symptoms, variability and asymmetry of the disease presentation, several treatment approaches and their divergent outcomes make PD enormously heterogeneous. In this work we hypothesized that not considering the disease heterogeneity might have been an adequate cause for the discrepant results in aforementioned studies. We show that not accounting for the disease variability might indeed compromise the results and invalidate the consequent interpretations. Accordingly, we propose and formalize a statistical approach to account for the intra and inter subject variability. This might help to minimize this bias in future motor fMRI studies revealing the functional brain dysfunction and contribute to the understanding of still unknown pathophysiological mechanisms underlying PD.
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Eichner, Cornelius. "Slice-Accelerated Magnetic Resonance Imaging." Doctoral thesis, Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-184944.
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This dissertation describes the development and implementation of advanced slice-accelerated (SMS) MRI methods for imaging blood perfusion and water diffusion in the human brain. Since its introduction in 1977, Echo-Planar Imaging (EPI) paved the way toward a detailed assessment of the structural and functional properties of the human brain. Currently, EPI is one of the most important MRI techniques for neuroscientific studies and clinical applications. Despite its high prevalence in modern medical imaging, EPI still suffers from sub-optimal time efficiency - especially when high isotropic resolutions are required to adequately resolve sophisticated structures as the human brain. The utilization of novel slice-acceleration methods can help to overcome issues related to low temporal efficiency of EPI acquisitions.
The aim of the four studies outlining this thesis is to overcome current limitations of EPI by developing methods for slice-accelerated MRI. The first experimental work of this thesis describes the development of a slice-accelerated MRI sequence for dynamic susceptibility contrast imaging. This method for assessing blood perfusion is commonly employed for brain tumor classifications in clinical practice. Following up, the second project of this thesis aims to extend SMS imaging to diffusion MRI at 7 Tesla. Here, a specialized acquisition method was developed employing various methods to overcome problems related to increased energy deposition and strong image distortion. The increased energy depositions for slice-accelerated diffusion MRI are due to specific radiofrequency (RF) excitation pulses. High energy depositions can limit the acquisition speed of SMS imaging, if high slice-acceleration factors are employed. Therefore, the third project of this thesis aimed at developing a specialized RF pulse to reduce the amount of energy deposition. The increased temporal efficiency of SMS imaging can be employed to acquire higher amounts of imaging data for signal averaging and more stable model fits. This is especially true for diffusion MRI measurements, which suffer from intrinsically low signal-to-noise ratios. However, the typically acquired magnitude MRI data introduce a noise bias in diffusion images with low signal-to-noise ratio. Therefore, the last project of this thesis aimed to resolve the pressing issue of noise bias in diffusion MRI. This was achieved by transforming the diffusion magnitude data into a real-valued data representation without noise bias. In combination, the developed methods enable rapid MRI measurements with high temporal efficiency. The diminished noise bias widens the scope of applications of slice- accelerated MRI with high temporal efficiency by enabling true signal averaging and unbiased model fits. Slice-accelerated imaging for the assessment of water diffusion and blood perfusion represents a major step in the field of neuroimaging. It demonstrates that cur- rent limitations regarding temporal efficiency of EPI can be overcome by utilizing modern data acquisition and reconstruction strategies.
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Graser, Anno. "MRT der Prostata." Diss., lmu, 2006. http://nbn-resolving.de/urn:nbn:de:bvb:19-48692.
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Filos, Jason. "Parallel Transmission MRI." Thesis, Imperial College London, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.516789.
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Kořínek, Radim. "Rychlé MRI metody." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2010. http://www.nusl.cz/ntk/nusl-218408.
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This thesis deals with comparison of rapid and conventional methods used in MRI (Magnetic Resonance Imaging). There is a description of imaging methods such as EPI (Echo Planar Imaging), Ultra-fast GRE, FSE (Fast spin echo) as well as a snapshot-FLASH and FISP (Fast Imaging with Steady Precession). Experimental part of this thesis deals with the rapid FSE (Fast Spin Echo) method. Especially is explained and assembled an algorithm for proper compilation of data from the FSE method. This algorithm allows us to evaluate the images from the FSE method. This method is examined in detail (in terms of impact parameters) and compared with traditional conventional methods. Finally, the individual images are evaluated, and the best parameters for FSE method are identified.
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Kaka, Shwan. "Advanced functional MRI." Thesis, University of Sheffield, 2015. http://etheses.whiterose.ac.uk/9962/.
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Functional Magnetic Resonance Imaging (fMRI) has been widely used to study the responses of the somatosensory cortex, motor cortex and associated neuronal activity in the human cerebral cortex. fMRI is a non-invasive and indirect method for mapping brain activity through measurement of the hemodynamic responses associated with electrical neuronal activity and the neural activity leads directly to changes in blood flow, blood volume and the cerebral metabolic rate of oxygen consumption. Non-invasive neuroimaging technologies such as functional MRI have both advantages, such as good spatial resolution, and disadvantages, such as poor temporal resolution. Some of the disadvantages have been alleviated by incorporating other techniques such as optical spectroscopy or electroencephalography (EEG) which are also non-invasive. All these techniques are sensitive to the vascular response of neuronal activity but in addition we are now investigating the existence of a weak direct electromagnetic effect with advanced fMRI. This neuronal current effect which gives rise to main magnetic field modulation should provide additional information for studying nerve characteristics. In this thesis, methods for fMRI mapping of responses from phantoms, the median nerve, the visual system, the motor sensory cortex and the thalamus are optimised and subsequently quantified. The experimental results strongly support the main hypothesis of the thesis and suggest that the generated magnetic field due to ionic current can be detected by present generation MRI using specific experimental designs and stimulation paradigms. Overall our results show that ionic currents in subjects can generate percentage signal changes in MRI up to 0.1± 0.01% corresponding to mean magnetic axonal fields of 0.7± 0.1nT with a Signal to Noise Ratio (SNR) of 3:1. The responses of the median nerve, motor sensory cortex and thalamus were detected using transcutaneous electrical nerve stimulation (TENS) and the visual cortex using strobe light stimulation in the range of frequencies 2.1 Hz to 4.1 Hz. All these measurements were acquired at 1.5T. Fast fMRI experiments using TENS and finger tapping were also acquired simultaneously. In addition, real and imaginary finger tapping experiments were performed in the motor sensory cortex at 3T. Our results imply that axonal fields that are generated due to action potentials can generate effects on MRI sensitive enough to directly detect neuronal activity using advanced fMRI, although sensitivity is still not fully adequate for clinical use.