En microscopie IRM, la sensibilité de détection est critique pour obtenir des images avec un rapport signal sur bruit suffisant car l’intensité du signal RMN devient extrêmement faible. Une stratégie alternative à l’utilisation de champs statiques élevés consiste à améliorer les performances des antennes radiofréquences qui détectent le signal d’IRM. Plus particulièrement, la stratégie dans laquelle s’inscrit ce travail de thèse vise à exploiter la haute sensibilité des antennes miniatures supraconductrices basées sur le principe des résonateurs monolithiques à ligne de transmission avec comme objectif à terme la mise en réseau de ce type d’antennes. Le développement d’un tel réseau représente un enjeu instrumental majeur car cela permet de profiter de la haute sensibilité intrinsèque des antennes miniatures supraconductrices tout en autorisant l’observation de zones étendues ou en profondeur. Cependant, les caractéristiques géométriques de ces antennes et la nature des matériaux utilisés posent des difficultés importantes pour réaliser les opérations d’accord, d’adaptation, ou découplage mutuel lors de leur utilisation en IRM. Dans le cadre de cette thèse, nous avons conduit des travaux abordant ces différentes problématiques et permettant la mise œuvre d’un réseau supraconducteur pour l’imagerie haute résolution à champ clinique.Nous avons développé en premier lieu un système permettant de réaliser automatiquement et sans contact l’accord et l’adaptation des antennes miniatures monolithiques. Ce système utilise des techniques, basées sur le couplage électrique et magnétique, que nous avons préalablement étudiées en utilisant différentes méthodes. Les performances de ce système ont été étudiées et la faisabilité de sa mise en œuvre dans une expérience d’IRM a été établie.Nous avons abordé en second lieu le problème de découplage mutuel des éléments constituant un réseau. Pour cela, des techniques de découplage potentiellement compatibles avec les antennes miniatures supraconductrices ont été étudiées. En particulier, la technique de découplage par anneau de blindage a été investie en profondeur, par simulation numérique et expérimentalement, et nous avons développé un modèle analytique d’optimisation du niveau de découplage accessible par cette technique. Nous avons mis en œuvre et validé cette technique avec des réseaux en cuivre de quatre antennes et des premiers essais ont été conduits avec un réseau constitué de deux antennes miniatures supraconductrices. / In MRI microscopy, the sensitivity of the detection is a critical issue for acquiring images with high signal to noise ratio because the amount of NMR signal is extremely low. An alternative to the use of high field strength is to improve the performances of the radiofrequency coil that detect the NRM signal. In particular, the strategy underlying the present work aims at exploiting the high sensitivity of miniature superconducting coils based on the monolithic design of transmission line resonators, with the long term objective of implementing an array of these coils. The development of such array represents an important instrumental stake since it allows for benefiting from the intrinsically high sensitivity of miniature superconducting coils while allowing the observation of extended region of interest. However, the highly compact structure, the small size of the coil and the nature of the material used make rise important difficulties for achieving the tuning, matching and mutual decoupling when using these coils in MRI. In the frame of this PhD project, with conducted works to address these problematics and allow for implementing a superconducting array for high resolution imaging at clinical filed strength.We have firstly developed a control system which allows for automatic and contactless tuning and matching of miniature monolithic coils. This system uses techniques based on electric and magnetic coupling, that we beforehand investigated using various methods. The performances of this system were studied and the feasibility of implementing it in an MRI experiment was established.The second part of this work addresses the issue of mutual decoupling between the elements of an array elements. To this end, decoupling techniques being potentially compatible with miniature superconducting coils have been studied. In particular the decoupling technique using shielding rings has been deeply investigated, by numerical simulation and experimentally, and we have developed an analytical model for optimizing the decoupling level achievable with this technic. We have implemented and validated this technic with a four-element copper coil array and first trials were performed with an array of two miniature.superconducting coils.

Hypertrophic cardiomyopathy (HCM), a heart-related abnormality, is the most prevalent cause of sudden death in young athletes at sporting events. A cluster of cardiomyopathy mutations are localized in β-cardiac myosin at the N-terminal region of subfragment-2. Using resonance energy transfer probes, a synthetic peptide model system was developed to study stability of the coiled coil (S2 fragment) structure by determining monomer-dimer equilibrium of the peptide. Fluorescence resonance energy transfer and MacroModel software suite were used to obtain distance measurements along with measurement of coiled coil formation. The model peptide was used to characterize the effects of disease-causing-mutations and examine potential candidate drugs (polyamines) to counteract effects of mutations causing HCM. Distance measurements between donor and acceptor probes obtained by computational simulation and fluorescence resonance energy transfer (FRET) were consistent. Measurements also agreed with simulations of unlabeled wildtype, indicating coiled coil structural stability of the peptide. Interaction of the site-specific antibody with the peptide strongly inhibited dimerization and destabilized coiled coil structure of the peptide. Presence of negatively charged glutamate residues in the region of subfragment-2 strongly suggested a potential interaction site for positively charged polyamines. Binding of certain polyamines, such as poly-L-Lysine 11 residues and poly-D-Lysine 17 residues, demonstrated the ability to enhance dimerization and improve stability of the coiled coil structure, while some other polyamines were shown to have insignificant impact on the structure. In an attempt to characterize the effect of HCM-causing-mutations, peptides containing E924K mutation and lethal mutation E930 deletion were synthesized. Fluorescence resonance probes were conjugated to the mutant peptides to determine coiled coil formation. Results obtained from both dynamic simulations and resonance energy transfer experiments indicated that these mutations strongly inhibit dimerization, and thus, destabilize coiled coil structure of the peptide. Further experiments were conducted using heterodimers containing a chain of wildtype and a chain of mutant peptide. Both E924K & Edel930 mutations destabilized coiled coil formation and prevented dimerization. This peptide model system would provide a promising tool for drug development targeting HCM-causing-mutations along the S2 region of myosin.

Protein folding studies have provided important insights about the key role of non-covalent interactions in protein structure and conformational stability. Some of these interactions include salt bridges, cation-π, and anion-Ï€ interactions. Understanding these interactions is crucial to developing methods for predicting protein secondary, tertiary, quaternary structure from primary sequence and understanding protein-protein interactions and protein-ligand interactions. Several studies have described how the interaction between two amino acid side chains have a substantial effect on protein structure and conformational stability. This is under the assumption that the interaction between the two amino acids is independent of surrounding interactions. We are interested in understanding how salt bridges, cation-π, and anion-π interactions affect each other when they are in close proximity. Chapter 1 is a brief introduction on noncovalent interactions and noncovalent interaction cooperativity. Chapter 2 describes the progress we have made measuring the cooperativity between noncovalent interactions involving cations, anions and aromatic amino acids in a coiled-coil alpha helix model protein. Chapter 3 describes cooperativity between cation, anion, and nonaromatic hydrophobic amino acids in the context of a coiled-coil alpha helix. In chapter 4 we describe a strong anion-π interaction in a reverse turn that stabilizes a beta sheet model protein. In chapter 5 we measure the interaction between a cysteine linked maleimide and two lysines in a helix and show that it is a general strategy to stabilize helical structure.

No presenta resumen. / Revisión por pares

By generating a synthetic CT image (sCT) directly from the MRI, the electron density can be calculated, and the CT examination can be excluded from the patient flow minimizing the risk of uncertainties in the registration. Basing the radiation treatment process solely on MR images is called MRI-only and is beneficial for the patient as it can provide more accurate radiation treatment than the standardised treatment with fewer CT examinations and possibly a more cost-effective radiation treatment process.  The conventional coils that are normally used in MRI for dose planning purpose cannot be placed directly on the patient as the outer body contour then can be deformed by these relatively heavy coils. The coils are therefore placed on a special holder which creates distance between the coil and the patient, this degrades the signal to noise ratio (SNR). The department for radiation treatment at Linköping University Hospital has access to a newly developed coil with so-called Air Technology. This type of coil is significantly lighter than the conventional ones and the idea is that this coil can be placed directly on the patient without causing deformation.  The aim of this project is to develop a software tool to validate an MRI-only workflow and to investigate if the radiation dose calculation based on sCT data differs from calculations based on CT data. Furthermore, to examine if the AIR coil has any effect on the body contour and the calculated dose.  For the evaluation of the AIR coil three similarity comparison methods were used, Hausdorff distance, Dice similarity coefficient (DSC) and Surface DSC. The result for the Hausdorff distance showed that eight out of eleven comparisons were within 4 mm difference, this corresponded good with Surface DSC where eight out of eleven had a result over 99% at a 3 mm tolerance. DSC measures gave above 98.5% for nine out of eleven of the comparisons.  The investigation on whether the radiation dose calculation differed was done using the dose- volume histogram statistics in Eclipse. A method calculating the gamma index was implemented in MICE. The results showed that nine out of ten gamma indexes had deviations that were within the same range. An explanation for why the results of one patient were not within the same range as the others could not be found and needs further investigations.

For a long time voltage spikes has been seen in measurement data from accelerator magnets during current ramps. These has been believed to be caused by movements, but has never before been studied in depth. The purpose of this thesis is therefore to prove, or disprove, that these events are caused by movements and to analyse what kind of displacements that actually occur. Measurement data from coil voltage, magnetic pick-up coils and current during transients has been acquired and analysed for the Nb3Sn-dipole magnets FRESCA2 and 11T models—named MBHSP107 and MBHSP109. The measurement data is compared to movement simulations that was done with the ROXIE-program, which is used to calculate mutual inductance change for a number of different movement types. The study strongly suggests that the transients are caused by movements, and also indicates that the maximal length of a single slip-stick motion can be up to around 10 micrometers, mostly in the direction of the magnet’s internal forces. The study has proven that transients in measurement data occur due to coil movements, and that these can be quantified—a discovery that can possibly affect future construction and design of accelerator magnets.

Wireless inductive power transfer systems are the only viable option for transferring energy to a moving vehicle. In recent years, there has been a great deal of interest in in-motion vehicle charging. The dominant technology thus far for in motion charging is elongated tracks, creating a constant eld for the moving vehicle. This technology suers from high volt ampere ratings and lower efficiency of 70%. On the other hand, stationary charging systems can demonstrate efficiency up to 95%. This thesis proposes lumped coils, similar to stationary charging coils for in-motion electric vehicle charging application. This novel primary coil architecture introduces new challenges in optimization and control. Traditional design of wireless inductive power transfer systems require designer experience, use of time consuming 3D FEM algorithms and lacks the comprehensive nature required for these systems. This thesis proposes two new optimization algorithms for the design problem which are comprehensive, based on only analytical formulations and do not need designer experience. There are challenges in the control of power transfer as well. Higher efficiency comparable to stationary systems can only be realized with proper synchronization of primary voltage with the vehicle position. Vehicle position detection and communication introduce significant cost and convenience issues. This thesis proposes a novel control algorithm which eliminates the need for vehicle position sensing and yet transfers the required percentage of energy. Both the optimization and control algorithms are verified with hardware setup.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19310号 / 工博第4107号 / 新制||工||1633(附属図書館) / 32312 / 京都大学大学院工学研究科電気工学専攻 / (主査)教授 山川 宏, 教授 松尾 哲司, 准教授 中村 武恒 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Molecular structures of biomaterials have close relation to their functions. We are interested in how biological building blocks assemble into the structures of native biomaterials and the hierarchy of those structures. We tackled the problem mainly with X-ray diffraction experiments and developed a thorough analysis technique to assign the X-ray signals to protein secondary structures and chitin. Three different types of biomaterials were examined: vimentin fibres, squid pens, and human hair. In vimentin fibres, we found that the secondary protein structures play an important role in the strength of the fibres. In native squid pens, we found a self-similar, hierarchical structure from millimetres down to nanometres. In human hair, we compared the signals corresponding to keratin proteins, intermediate filaments, and lipids between different subjects, and found small deviations. The structures of these three biomaterials, which encompass different orders of length scales, were described both quantitatively and graphically. We hope that this work will eventually allow us to understand how and why nature builds biomaterials this way. / Thesis / Master of Science (MSc)

No description available.