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Yao, Zhen. "OPTIMIZING RF AND GRADIENT COILS IN MRI." Case Western Reserve University School of Graduate Studies / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=case1402058570.
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Jones, Alexa. "Radio frequency coils for ultra-high field MRI." Thesis, University of Nottingham, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.490979.
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The push toward higher magnetic fields in MRI has consistently thrown up new challenges in hardware development. The recent development of a new generation of ultra-high field scanners for human imaging is no exception. The earch presented in this thesis aims to provide solutions to new technical challenges in radio-frequency probe design. All probe designs were developed for use at 7T on a Philips Acheiva full body scanner.
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Farhat, Sedig. "Radiofrequency coils for ultra-high field body MRI." Thesis, University of Nottingham, 2013. http://eprints.nottingham.ac.uk/28847/.
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In this thesis, the probes were modelled and constructed at the SPMMRC. All measurements were performed on a 7T Philips scanner. The coils have been successfully evaluated. The dipole, loops, strip line and wrist probes for imaging the pelvis, knee and wrist were tested for clinical use at 7T. Two elements wrist coil can pick up signals from the whole region of interest. The advantage is more uniformity of field of view and better sensitivity. The in vivo MRI images acquired in the wrist showed the two elements provided the good quality images for the human wrist. The second study is microstrip line probe. The current flows over the flat-strip were computed, it showed that a significant increase of current close to the edges. This result agrees with theory. We did not use the strip line coil to image a human body, because the coil generated a high SAR/B1 +2 level in the region of interest. The third study was of a coil of two square loops. One way of achieving decoupling is to use the overlapping technique to decouple the coils in the simulation. It produced high signal-to-noise ratio and provides a large field of view. Finally, the dipole has been developed for in vivo MRI applications. We presented a novel model for determining the length of the PECs required for tuning the dipole at 298 MHz. The efficiency, field of view and homogeneity were improved by adding the flat strip, two strips and array strips dipole. The SAR/B1 +2 generated by the dipoles was much less than produced by the loop coil and strip line coil in the pelvis. The dipoles showed the desired improvement in SNR and homogenous coverage. Coverage goes much further into the pelvis and knee as well.
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BAIG, TANVIR N. "NEW DIRECTIONS IN THE DESIGN OF MRI GRADIENT COILS." Case Western Reserve University School of Graduate Studies / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=case1169749200.
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Williams, Guy Barnett. "Novel geometry gradient coils for MRI designed by genetic algorithm." Thesis, University of Cambridge, 2001. https://www.repository.cam.ac.uk/handle/1810/244812.
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This thesis concerns the design of gradient coils for magnetic resonance imaging systems. The method of design by genetic algorithm optimisation is applied to novel gradient geometries both by use of conventional computer facilities, and, by parallelisation of the design algorithm, on a supercomputer architecture. Geometries and regions of interests which are inaccessible to analytic solution are considered, and the criteria which are difficult to include in such algorithms, such as the robustness of the design, are also included. To exemplify this, in the first instance a two axis biplanar coil was designed and the performance of the genetic algorithm tested and evaluated. The coil was tested computationally; a working example was constructed and tested in a MRI scanner both on phantom objects and on a human knee. Consideration of the usefulness of the coil regions not optimised for linearity for image reconstruction was done. The gradient efficiencies of the final designs in the z and y directions respectively were 0.3 mTm-1A-1 and 0.4 mTm-1A-1 over a 15 cm diameter region of interest. The size of the interior of the gradient set was designed to be 40.0 cm x 24.4 cm x 40.0 cm, to fit within the confines of the bore of an existing scanner. The linearity in the primary direction over the region of optimisation was less than 5% for both coils. The algorithm was extended for operation on a Hitachi SR2201 supercomputer using parallelisation. The performance in this mode was evaluated and found to be favourable in comparison with the standard computer architecture, with an increase in speed in real time of a factor of-!llore than 40 in some configurations of the supercomputer. Various polygonal cross-section design shapes requiring the use of this improved computer performance were optimised and evaluated computationally. Such designs have previously been inaccessible to the genetic algorithm optimisation model. Tests were made between the performance of the genetic algorithm on various similar design problems, and simulated images from such gradient coils were produced. Finally an example of a transverse coaxial return path gradient coil is presented computationally. This coil had an internal diameter of 32 cm, a d external diameter of 44 cm and a length of 40 cm. It achieved a strength of 0.1 mTm- 1A -1 over a cylinder of diameter 20 cm and length 25 cm, with a deviation from linearity of less than 5% over this volume.
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Papoutsis, Konstantinos. "Construction and characterisation of MRI coils for vessel wall imaging at 7 tesla." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:bd44e9b5-7600-4861-ba38-f324d4395165.
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Atherosclerotic plaques in the bifurcation of the carotid artery vessels can pose a significant stroke risk from stenosis, thrombosis and emboli, or plaque rupture. However, the possibility of the latter depends on the structure of the plaque and its stability. So far, the assessment of such depositions, and the evaluation of the risk they pose, is not satisfactory with 3 Tesla black blood imaging. It is expected that the SNR increase at 7 Tesla, together with an appropriate and patient-safe RF coil, will result in higher resolution images that would help in better assessing the composition of atherosclerotic plaques in vessel walls. A custom-built neck array was designed and constructed, with the aim of investigating the benefits of the higher field strength using DANTE-prepared black blood imaging. A 4-channel transmit array was designed to generate the required <b>B</b><sup>+</sup><sub style='position: relative; left: -.5em;'>1</sub> field for the DANTE module to be used. A separate close fitting 4-channel receive array was preferred for improved SNR and parallel (receive) imaging. Geometric, active, passive as well as preamp decoupling schemes were employed for adequate isolation between the arrays and their channels. Electromagnetic simulation software, Semcad X (SPEAG, Zurich), was used for safety assessment with human phantoms (Virtual population). The <b>E</b> fields for 1 W transmission per channel were calculated for each element for a worst case SAR estimation. The transmission power limits per channel were set according to the 10g SAR limit set in IEC 60601. For simulation validation, temperature measurements and surface heat mapping were performed on a meat phantom. Finally, a healthy male subject was scanned using a protocol consisting of <b>B</b><sub>1</sub> mapping, RF shimming at an ROI, and 2D and 3D DANTE prepared Gradient Echo (GRE). The worst-case heating scenario, as defined in the methods section, generated a maximum local SAR of 7.65 W/kg for 1 Watt per channel input. Thus, for 1st level mode (20W/kg max), the power limit was set at 2.6 W per channel. The heating profile was similar to that simulated and the measured temperature increase was within a ±10% margin relative to the simulation. The global SAR power limit per channel was found to be higher (i.e. more allowed power) than the worst case local SAR power limit, and thus did not impose additional power penalty. The resolution achieved was 0.6 mm isotropic for the 3D protocol and 0.6 by 0.6 by 2.5 mm for the 2D protocol. The average SNR was measured within the vessel wall location of the two carotid arteries and found to be 27±6 for the DANTE images and for the static tissue closer to the skin the SNR was 55±2. In conclusion, a 4Tx/4Rx coil was designed to target the carotid arteries operating under pTx mode and a black blood imaging sequence was implemented for blood signal suppression and vessel wall imaging. The initial results from the subject and phantom imaging show satisfactory blood suppression and spatial resolution.
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Cheong, Hoon Sin. "Cryogenically-cooled high temperature superconducting (HTS) coils for low field MRI." Thesis, University of Sheffield, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.575382.
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In low field MRl (<0.5T), the signal-to-noise ratio (SNR) is predominantly degraded by thermal noise of the imaging coil when the sample loading is minimized. This means surface coils made of high temperature superconductors (HTS) should have an SNR significantly higher than their room-temperature copper equivalents due to the reduction in resistivities. While this hypothesis has been reportedly validated, the actual efficacy of HTS coils is still debatable as the benchmark setups in the prior art had an unfavorably large coil-to-sample separation which diminished the SNR yield. This thesis is intended to perform a quantitative validation on the said hypothesis against a novel benchmark setup where the equivalent room-temperature copper coil was placed directly next to the sample to achieve the best SNR sensitivity. The HTS coil used was an YBCO surface coil having a l0-tum, 70mm-circular spiral layout. For sufficient thermal insulation, there was a 10mm gap between the YBCO coil and the sample while the sample separation for the copper coil was merely I mm. By studying the simulated B1 sensitivity profile of the designated layout, the sample loss and intrinsic resistance of both coils were calculated to allow a theoretical evaluation on the research hypothesis. Each coil was then fabricated and configured with an inductively-coupled matching circuit. The quality factors (Q) of the coils in different loading conditions were measured to allow an empirical estimation on the SNR advantage of the YBCO coil. Both coils were then tested on a saline phantom in a 0.17T MRI system where in-vivo hand images were also acquired. The results showed that the YBCO coil had an SNR gain of 2.0 over the proposed benchmark setup. Such a finding is a valuable addition to the prior art as the efficacy of HTS coils for low field MRl was conclusively proven.
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Wong, Eddy Yu Ping. "Optimization of Micro Antennas for Interventional / Intravascular MRI." online version, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=case1117225501.
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Obi, Aghogho A. "A Method Of Moments Approach for the Design Of RF Coils for MRI." Digital WPI, 2008. https://digitalcommons.wpi.edu/etd-dissertations/284.
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Magnetic Resonance Imaging (MRI) is a widely used soft-tissue imaging modality that has evolved over the past several years into a powerful and versatile medical diagnostic tool capable of providing in-vivo diagnostic images of human and animal anatomies. Current research efforts in MRI system design are driven by the need to obtain detailed high resolution images with improved image signal-to-noise ratio (SNR) at a given magnetic field strength. Invariably, this requirement demands the development of high performance MRI radio frequency (RF) coils. However, the complexities and stringent requirements of modern clinical MRI systems necessitate the development of new modeling methodologies for the design of high performance RF coils. This dissertation addresses this need by developing a distinct Method of Moments (MoM) modeling approach suitable for the simulation of RF coils loaded with biological tissues. The unique implementation utilizes two distinct basis functions in order to collectively describe the surface current density on the RF coil, and the sum of the volume current density and the displacement current density in the associated biological tissue. By selecting basis functions with similar properties to the actual physical quantities they describe, we avoided spurious solutions normally associated with MoM based implementations. The validity of our modeling method was confirmed by comparisons with analytical solutions as well as physical measurements, yielding good agreement. Furthermore, we applied the MoM based modeling method in the design and development of a novel 4-channel receive-only RF coil for breast imaging in a clinical 1.5T system. The new coil design was inspired by the multi-channel array concept, where multiple conducting strips were arranged in an anatomically conforming profile with the intention of improving sensitivity and SNR. In addition, the coil structure featured an open breast coil concept in order to facilitate MRI-guided biopsy and patient comfort. A comparison of simulation results and actual physical measurements from the prototype RF coil demonstrated good agreement with one another. Also, imaging tests were conducted on a pair of MRI phantoms as well as on a human patient after obtaining proper authorization. The tests revealed good magnetic field homogeneity and a high SNR in the region of interest. In addition, performance comparisons between the prototype 4-channel RF coil and existing high end clinical 4-channel RF breast coils indicated an achievement of superior SNR in conjunction with very good magnetic field homogeneity. Currently, the prototype 4-channel RF coil has outperformed all existing high end clinical 4-channel RF coils used in comparison studies.
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Zakszewski, Elizabeth K. "Off-resonance and detuned surface coils for B₁ inhomogeneity in 7-Tesla MRI." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/41593.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2006.<br>"June 2006."<br>Includes bibliographical references (p. [34]).<br>A problem with high-field MRI is the lack of B1 homogeneity, particularly signal cancellation in the outer parts of the head. Here we attempt to correct this by adding surface coils. To adjust the mutual coupling, we vary the resonance properties of the added coil. A new agar-based head phantom was built, and two surface coils were built and tuned. The surface coils were placed in various configurations against the phantom to modify the B1 field with their presence, while images were taken using a 16-rung birdcage coil to transmit and receive. Trials were taken with various spacings between the surface coil and the phantom, while the resonance of the surface coil was either shifted in frequency by changing the voltage across a varactor diode, or detuned using a resonant detuning circuit. It was discovered that with a 1 cm spacing and a surface coil tuned just above resonance, SNR near the surface coil could be improved by upwards of 400%, with the trade-off of a reduced signal in other areas on the periphery of the head. Other configurations could achieve better B1 homogeneity at the expense of reduced SNR throughout the head. Future studies will explore the possibility of using more than one surface coil to improve SNR in more places on the periphery of the head.<br>by Elizabeth K. Zakszewski.<br>S.B.
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Tadesse, Yonatan Abebe. "The Electromagnetic Simulation of Birdcage Coils for MRI based on Finite Element Method." Youngstown State University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ysu1484137190762487.
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Tobgay, Sonam. "Novel concepts for RF surface coils with integrated receivers." Link to electronic thesis, 2004. http://www.wpi.edu/Pubs/ETD/Available/etd-0419104-141545.
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Jayatilake, Mohan L. "Optimization and construction of passive shim coils for human brain at high field MRI." University of Cincinnati / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1313772791.
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Esmail, A. A. "The development of a compact magnetic resonance imaging (MRI) system using novel receive coils." Thesis, London South Bank University, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.618662.
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Ireland, Christopher M. "Radiofrequency Coils for Faster and Quieter MR Imaging on a Neonatal MR System." University of Cincinnati / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1595499514975611.
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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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<p>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.</p>
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Bhuiyan, E. H. "Monitoring movement in MRI by measuring changes in the EMF induced in head-mounted coils." Thesis, University of Nottingham, 2017. http://eprints.nottingham.ac.uk/44443/.
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Image quality is degraded by involuntary movement of the subject in an MRI scanner. It is fairly challenging in MRI of the brain to monitor the involuntary head movement accurately. Though there are a few techniques to monitor head movement of the subject for prospective motion correction, it is still an unsolved problem in MRI. In this study, head movement inside an MR scanner is monitored via measurement of changes in the voltage induced in head mounted coils by switched magnetic field gradients. The motion of a rigid body such as the human head is decomposed into two components: namely translation and rotation. There are three degrees of freedom (DOFs) for translational motion i.e. translation along the x, y and z axes and three rotational degrees of freedom for rotational motion i.e. rotation about the x, y and z axes. Head movement is monitored in a gradient field by measuring the change in induced voltage in head mounted coils. To calculate the change in induced voltage I follow two approaches: circular loops simulation, analytical as well as numerical calculations. I show that by using a standard method one can form a linear model to identify the position and orientation of the coils. An experimental arrangement is set up to check the validity of the analytical and numerical calculations. Experiments carried out with a rig of five coils verified that the changes in induced voltage in the coils is linear with respect to the changes in position of the coils. The linear model is also verified by comparing estimated positions obtained by using the coils to those found by image realignment of fast field echo (FFE) images using Statistical Parametric Mapping (SPM). We experimentally evaluate the new approach for monitoring head movement inside an MR scanner, which exploits the linear variation of the voltages induced in a set of coils by time-varying magnetic field gradients with respect to small changes in position/orientation. This approach was tested by attaching five coils to a structured agar phantom and a healthy volunteer's head. The results suggest that it is possible to estimate the position and orientation with 0.22 mm and 0.24˚ root-mean-square error using this set-up. The new approach could be used for prospective or retrospective motion correction. An experiment is also carried out by using free running EPI (Echo Planar Imaging) to track the head movement inside an MR scanner. There is a strong relation between head movement and EPI waveforms, the central point of the experiment is to track the head displacements via measuring induced voltage in the coils by using EPI waveforms during execution of free running EPI. The results obtained from the experiment reveal that the method is promising.
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Gudino, Natalia. "Control of Intravascular Catheters Using a 3D Array of Active Steering Coils for and Interventional MRI setting." Case Western Reserve University School of Graduate Studies / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=case1216731566.
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Dalveren, Taylan. "A Study of Sensitivity Mapping Techniques for Multi-Channel MR Coils." University of Akron / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=akron1373403690.
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IBrahim, Tamer S. "Design of Radiofrequency Coils for Magnetic Resonance Imaging Applications: A Computational Electromagnetic Approach." The Ohio State University, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=osu1041281167.
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Lemdiasov, Rostislav A. "A general purpose computational approach to the design of gradient coils for arbitrary geometries." Worcester, Mass. : Worcester Polytechnic Institute, 2004. http://www.wpi.edu/Pubs/ETD/Available/etd-09214-155502/.
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Badal, James A. "High-Resolution MRI for 3D Biomechanical Modeling: Signal Optimization Through RF Coil Design and MR Relaxometry." BYU ScholarsArchive, 2014. https://scholarsarchive.byu.edu/etd/3841.
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Computed Tomography (CT) is often used for building 3D biomechanical models of human anatomy. This method exposes the subject to a significant x-ray dose and provides limited soft-tissue contrast. Magnetic Resonance Imaging (MRI) is a potential alternative to CT for this application, as MRI offers significantly better soft-tissue contrast and does not expose the subject to ionizing radiation. However, MRI requires long scan times to achieve 3D images at sufficient resolution, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR). These long scan times can make subject motion a problem. This thesis describes my work to reduce scan time while achieving sufficient resolution, SNR, and CNR for 3D biomechanical modeling of (1) the human larynx, and (2) the human hip. I focused on two important strategies for reducing scan time and improving SNR and CNR: the design of RF coils optimized to detect MRI signals from the anatomy of interest, and the determination of MRI relaxation properties of the tissues being imaged (allowing optimization of imaging parameters to improve CNR between tissues). Work on the larynx was done in collaboration with the Thomson group in Mechanical Engineering at BYU. To produce a high-resolution 3D image of the larynx, a 2-channel phased array was constructed. Eight different coil element designs were analyzed for use in the array, and one chosen that provided the highest Q-ratio while still meeting the mechanical constraints of the problem. The phased array was tested by imaging a pig larynx, a good substitute for the human larynx. Excellent image quality was achieved and MR relaxometry was then performed on tissues in the larynx. The work on the hip was done in collaboration with the Anderson group in orthopedics at the University of Utah, who are building models of femoral acetabular impingement (FAI). Accurate imaging of hip cartilage requires injection of fluid into the hip joint capsule while in traction. To optimize contrast, MR relaxometry measurements were performed on saline, isovue, and lidocaine solutions (all typically injected into the hip). Our analysis showed that these substances actually should not be used for MR imaging of the hip, and alternate strategies should be explored as a result.
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Hossein, Nezhadian Sajad. "Réseau flexible de résonateurs à ligne de transmissions pour l'émission et la réception en IRM cardiaque à 7T." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS492/document.
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Ce projet doctoral s’est déroulé dans le cadre d’une collaboration entre le laboratoire d’Imagerie par Résonance Magnétique Médicale et Multi-Modalités (IR4M) de l’Université Paris-Sud (France) et le Center for Medical Physics and Biomedical Engineering at Medical (CMPBME) de l’Université Médicale de Vienne (Autriche). L’objectif principal de ce travail était de développer un réseau d’antennes radiofréquence flexible fonctionnant en émission/réception pour l’IRM à 7T. Les réseaux d’antennes permettent de bénéficier du rapport signal sur bruit élevé des antennes de surface de petites tailles tout en accédant à un champ de vue étendu. De plus, les réseaux d’antennes permettent l’utilisation de technique d’imagerie parallèle afin d’accélérer l’acquisition des images ainsi que l’utilisation d’algorithme de transmission parallèle afin de produire un champ radiofréquence homogène, ce qui est crucial en IRM. Ce projet doctoral visait la conception, le développement, l’installation et l’évaluation d’un réseau d’antenne RF flexible basé sur le principe des résonateurs à lignes de transmission (RLT). Ces structures sont intrinsèquement monolithiques et auto-résonantes et ne nécessitent donc pas l’emploi de condensateurs discrets pour accorder l’antenne. Des simulations électromagnétiques 3D, ainsi que des caractérisations expérimentales sur table et en IRM ont été réalisées pour évaluer les performances de ce réseau, en configuration plate et courbée<br>This PhD thesis was conducted in the frame of a bilateral project between the laboratoire d’Imagerie par Résonance Magnétique Médicale et Multi-Modalités (IR4M) at Université Paris-Sud (Orsay, France) and the Center for Medical Physics and Biomedical Engineering (CMPBME) at the Medical University of Vienna (Vienna, Austria). The main objective of this work was to develop a flexible transceiver RF coil array for 7 T MRI. Coil arrays benefit from the high SNR of small surface coils over an extended field of view (FOV). Furthermore, array coils enable the use of parallel imaging (PI) techniques for accelerated image acquisition and pTx algorithms that can be used to produce a homogeneous transmit field which is of importance in MRI. This project targets the design, development, implementation and evaluation of a flexible RF coil array based on the transmission line resonator (TLR) principle. TLRs are inherently monolithic and self-resonant structures, i.e. there is no need for lumped element capacitors to tune the coil. 3D electromagnetic simulation (EMS) together with bench and MRI experiments were performed to evaluate the performance of the developed array in flat and bent configuration
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Jepsen, Peter Austin. "Improvements in Diffusion Weighted Imaging Through a Composite Body and Insert Gradient Coil System." BYU ScholarsArchive, 2013. https://scholarsarchive.byu.edu/etd/3700.
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Diffusion Magnetic Resonance Imaging (DMRI) is a class of Magnetic Resonance Imaging (MRI) techniques with broad medical applications ranging from characterization of tumors and brain damage to potential prediction of stroke. Gradient coil and signal-to- noise ratio (SNR) constraints limit spatial resolution, accuracy, and scan time in DMRI. Achieving high b-values (measures of a scan's sensitivity to diffusion) often require scans with long diffusion gradient pulses, leading to significant magnetic resonance (MR) signal decay before the signal can be sampled. This signal loss reduces the accuracy of diffusion parameter estimation. The ability to sample the MR signal sooner while maintaining the same b-value is restricted by the maximum amplitude and slew rate of gradient coils. A composite system utilizing body and high-powered insert gradient coils can achieve high b-values more quickly, enabling a shorter delay between excitation and signal sampling and improved accuracy of diffusion parameter estimation. Alternately, such a system can achieve higher b-values at an equivalent delay between excitation and signal sampling. This thesis describes the implementation of such a system, experiment design for evaluating the benefits of the system to DMRI, and design of a diffusion phantom. Also included are a characterization of a composite system's improvements to DMRI based on analysis of experimentally-obtained data and simulation results validating those findings. Finally, recommendations for further improvements to diffusion MRI are given.
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Ha, Yonghyun Verfasser], N. Jon [Akademischer Betreuer] [Shah, Dirk [Akademischer Betreuer] Heberling, and Joachim [Akademischer Betreuer] Mayer. "Development of novel RF coils for $^23}$Na imaging at ultra-high field MRI / Yonghyun Ha ; Nadim Joni Shah, Dirk Heberling, Joachim Mayer." Aachen : Universitätsbibliothek der RWTH Aachen, 2019. http://d-nb.info/1213993873/34.
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Ha, Yonghyun [Verfasser], N. Jon [Akademischer Betreuer] Shah, Dirk [Akademischer Betreuer] Heberling, and Joachim [Akademischer Betreuer] Mayer. "Development of novel RF coils for $^23}$Na imaging at ultra-high field MRI / Yonghyun Ha ; Nadim Joni Shah, Dirk Heberling, Joachim Mayer." Aachen : Universitätsbibliothek der RWTH Aachen, 2019. http://d-nb.info/1213993873/34.
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Salmón, Carlos Ernesto Garrido. ""Desenvolvimento e aplicações clínicas de um sistema integrado transdutor/bobinas de gradientes de alto desempenho para obtenção de imagens por ressonância magnética em 0.5 TESLA"." Universidade de São Paulo, 2005. http://www.teses.usp.br/teses/disponiveis/76/76132/tde-12032005-182218/.
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Este trabalho descreve o desenvolvimento de um sistema integrado transdutor/bobinas de gradientes de alto desempenho para Imagens por Ressonância Magnética. Este sistema é composto por um transdutor de radiofreqüência tipo sela e um conjunto de 3 bobinas locais assimétricas. No desenho do transdutor foram otimizados os parâmetros: relação sinal ruído e uniformidade do campo magnético por ele gerado. A densidade de corrente de cada bobinas local foi otimizada mediante técnicas numéricas estocásticas para gerar um gradiente de campo magnético uniforme em cada uma das 3 direções do espaço numa região das dimensões do crânio. O conjunto de bobinas de gradientes construído possui um diâmetro livre de 31.5 cm e gera em média 25 mT/m/A por bobina, com indutâncias inferiores a 310 mH. São mostradas as aplicações clínicas desenvolvidas nas áreas de imagens tridimensionais e angiografia, a partir das seqüências de pulsos implementadas e aproveitando o uso do sistema integrado, em um tomógrafo de ressonância magnética de 0.5 Tesla. Imagens de phantom foram adquiridas em menos de 500 ms usando o conjunto integrado e técnicas do tipo Echo Planar Imaging. Aspectos referentes à caracterização e correção de campos magnéticos estáticos e homogêneos são também comentados. As soluções descritas nesta tese têm um amplo conteúdo tecnológico e beiram nas fronteiras da Física Aplicada e a Engenharia Biomédica.<br>Here we describe the development of a high performance radio-frequency/gradient coil integrated system for Magnetic Resonance Imaging. A saddle radio-frequency coil and a three-axis asymmetric local gradient coil composed this system. Two parameters were optimized in the RF coil design: signal-to-noise ratio and magnetic field uniformity. The current density of each local coil was optimized using stochastic numerical techniques, in order to generate a uniform magnetic field gradient by axis in a region representing a human head. The build gradient coil set has an inner diameter of 31 cm. The average gradient efficient of the three-axis is 25 mT/m/A and the maximum inductance is less than 310 mH. We show the clinical applications performed in three-dimensional and angiography imaging areas in a 0.5 Tesla magnetic resonance tomograph. These applications were optimized to taking advantage from the integrated system. Phantom images were acquired in less than 500 millisecond using echo planar techniques and the integrated set. Some aspects about static and homogeneous magnetic field characterization and correction are also commented. In this work we described solutions with wide technologic content close to the boundaries of the Applied Physics and Biomedical Engineering.
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Nohava, Lena. "Concepts for Wearable Technology in MR : Lightweight Flexible Radio Frequency Coils and Optical Wireless Communication Flexible multi-turn multi-gap coaxial RF coils: design concept and implementation for Magnetic Resonance Imaging at 3 and 7 Tesla Perspectives in Wireless Radio Frequency Coil Development for Magnetic Resonance Imaging." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPAST069.
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Ce projet doctoral a été réalisé au laboratoire BioMaps de l'Université Paris-Saclay et au CMPBME de l'Université Médicale de Vienne. Afin d’améliorer la valeur diagnostique de l'IRM, il est souhaitable de réduire les durées d’acquisition, d’avoir une prise en charge plus efficace des patients et une meilleure qualité des images. Dans ce but, une instrumentation portable avec un matériel optimisé permettrait de réduire le poids, d’augmenter la flexibilité et de transmettre sans fil les signaux RMN, améliorant ainsi la sensibilité, le confort, la sécurité et la facilité d'utilisation de ces dispositifs.Dans ce contexte, nous avons étudié des antennes RF souples à câbles coaxiaux basées sur le principe des résonateurs à lignes à transmission. Ces résonateurs, pouvant posséder plusieurs tours et/ou plusieurs fentes, permettent d'optimiser la taille de l’antenne RF en fonction de l'application visée. Le concept a d'abord été étudiée in silico. De nombreux prototypes ont été construits et leurs performances ont été testées sur table et en IRM à 3 et 7 T. Les antennes coaxiales ont révélé avoir des performances robustes à la déformation, ne dégradent pas le TAS et peuvent améliorer le RSB et l'efficacité de transmission lorsqu'elles sont conformées au relief de la zone imagée. En parallèle, nous avons mené une étude approfondie des technologies de transmission sans fil en IRM. Un premier prototype de communication optique sans fil pour la transmission de données de capteurs de mouvements a été réalisé et testé. Les antennes coaxiales portables que nous avons étudiées offrent une alternative intéressante aux antennes standard en raison de leur faible poids et de leur flexibilité<br>This PhD thesis work was conducted at the BioMaps laboratory at the Université Paris-Saclay and the Center for Medical Physics and Biomedical Engineering (CMPBME) at the Medical University of Vienna.To improve diagnostic value in MRI, shorter acquisitions, more efficient patient handling and improved image quality are needed. Wearable technology with optimized hardware reduces weight, increases flexibility, and could be wireless, thereby improving sensitivity, comfort, safety, and usability.In this work, flexible self-resonant coaxial transmission line resonators were investigated. Coaxial coils with multiple turns and gaps enable size optimization depending on the target application. The design was first studied in silico. Numerous prototypes were constructed and their performance was tested on the bench and in 3 and 7 T MRI. Coaxial coils were shown to be robust against bending, have no SAR penalty and improve SNR and transmit efficiency when form-fitted.A review of wireless MR, associated hardware developments and data transmission technology is given.An optical wireless communication module for sensor data transmission was demonstrated experimentally.Wearable coaxial coils offer an attractive alternative to standard coils due to low weight and flexibility. With wireless motion sensors diagnostic value in e.g. breast, knee, or cardiac MRI could be increased
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Coutinho, Alessandra. "Avaliação da cartilagem da ATM por meio de ressonância magnética com a utilização de bobinas microscópicas." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/23/23139/tde-24102009-110244/.
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Diferenças na espessura e regularidade da cartilagem da articulação temporomandibular (ATM) ocorrem como o resultado de áreas em crescimento ou em remodelamento. Esse aspecto dificulta a interpretação clínica das imagens e geralmente negligencia a presença da fibrocartilagem. O estudo, por meio da Ressonância Magnética utilizando bobinas microscópicas, possibilita uma melhor observação da cartilagem articular. Confirmamos essa evidência por meio do estudo que analisou 20 indivíduos (40 ATM), divididos em grupo sintomático (DTM) com 10 pacientes (20 ATM) apresentando queixa clínica e suspeita diagnóstica de DTM e, o grupo controle com 10 voluntários (20 ATM) assintomáticos ou que não apresentavam sinais e sintomas clínicos de DTM. As imagens de RM sagitais oblíquas ponderadas em DP SPIR da ATM foram capazes de mostrar a cartilagem com melhor evidência tanto na cabeça da mandíbula quanto na eminência articular proporcionado mensurações, as quais se apresentaram estatisticamente iguais entre os grupos e também a avaliação da regularidade com o mesmo comportamento entre os grupos e geralmente acompanhando a morfologia da cortical óssea. Em muitos casos, principalmente quando da presença de deslocamento para anterior do disco articular, a observação se torna mais difícil, requerendo mais prática para esse tipo de avaliação. Observamos que pacientes do grupo controle apresentaram deslocamento de disco. Dessa maneira, consideramos um exame muito útil como auxiliar no diagnóstico da DTM, e com o desenvolvimento de novas terapias para doenças degenerativas e traumas na cartilagem, as imagens de RM com o uso de bobina microscópica são de crescente importância clínica e poderão desempenhar um papel importante na avaliação da eficácia dessas terapias.<br>Differences in thickness and regularity of the temporomandibular joints (TMJ) cartilage occur as the result of areas of growth or remodeling. This fact leads to misinterpretations on diagnosis and generally neglects the presence of fibrocartilage. The present study, using MRI microscopic coils, allows better observation of the articular cartilage. This evidence was confirmed by this study that examined 20 individuals (40 TMJ), divided into: symptomatic group with temporomandibular dysfunction (TMD) of 10 patients (20 TMJ) presenting clinical complaint and TMD diagnosis; and the control group of 10 volunteers (20 TMJ) that were asymptomatic or who had no clinical signs and symptoms of TMD. On both groups were measured cartilage thickness and if the cartilage was regular or not. The oblique sagital MR images of weighted SPIR protons density (PD\'s) TMJ were able to show the best cartilage images either in the mandibles head or on the articular eminence providing measurements. Both groups presented no statistically significant differences regarding to thickness and the evaluation of the regularity presented the same result. The regularity of the cartilage generally was similar to the morphology of the cortical bone. In many cases, especially when the presence of anterior articular disc displacement, the evaluation was more difficult, requiring practice. The control group with asymptomatic patients was found also to have disc displacements. Thus, we review a very useful tool in the diagnosis of TMD and its importance to evaluate the cartilage to development new therapies for degenerative diseases and trauma. The MRI images with the use of microscopic coil are of increasing clinical importance and might play an important role in assessing the effectiveness of these therapies.
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Guisiano, Jean-clément. "Développement d'un micro-dispositif intègre pour le contrôle de la fréquence de résonance d'une antenne à haute sensibilité pour l'IRM." Thesis, Paris 11, 2011. http://www.theses.fr/2011PA112163/document.
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L’utilisation d’antennes miniatures à haute sensibilité basées sur le principe des lignes de transmission a permis, lors de l’étude de pathologies chez l’Homme ou le petit animal , une amélioration significative de la qualité des images obtenues en micro Imagerie par Résonance Magnétique (IRM). Les performances élevées de ces antennes et leurs dimensions réduites entrainent cependant des difficultés critiques pour traiter et conditionner le signal de Résonance Magnétique Nucléaire (RMN) détecté. Plus particulièrement, le réajustement de la fréquence de résonance de l’antenne de détection, au cours d’une expérience d’IRM, ne peut être réalisé à l’aide de composants rapportés, comme c’est le cas avec les antennes d’IRM conventionnelles, ceci afin de ne pas dégrader leurs performances.Notre étude a consisté à développer deux techniques d’accord originales et dédiées aux antennes miniatures à lignes de transmission. Ces techniques sont basées sur le déplacement micrométrique d’un élément d’accord à proximité de l’antenne entrainant une variation de l’environnement électromagnétique de celle-ci, et donc de la fréquence de résonance, par couplage (diélectrique ou inductif). L’ensemble des résultats obtenus (par des caractérisations expérimentales, des simulations numériques et des modélisations analytiques) a servi de base à la conception et la réalisation d’un dispositif de micro-déplacement chargé d’assurer le réglage fin de la fréquence de résonance à travers le déplacement de l’élément d’accord.La mise en œuvre d’une antenne accordée à l’aide du dispositif a été réalisée au sein d’un imageur à 4,7 T. Des images de démonstration sur fantôme ont été obtenues et validées, montrant ainsi la pertinence d’un tel dispositif et la faisabilité de systèmes résonants auto-accordés dédiés à l’IRM haute sensibilité<br>The use of miniature transmission lines coils, in the study of diseases in humans or small animals, has allowed for significant improvements in Micro Magnetic Resonance Imaging (MRI). The high sensitivity of such coils combined with their small size, however, leads to critical problems in treating and conditioning the detected Nuclear Magnetic Resonance (NMR) signal. In particular, the adjustment of the resonant frequency of these detection coils, during a MRI experiment, cannot be achieved using reported components, as is the case of conventional MRI coils, in order not to degrade their performances.We have developed two original tuning techniques for such coils. These techniques are based on the micrometric displacement of a tuning element near the coil surface, which modifies the electromagnetic environment of the coil by coupling, resulting in a change of the resonant frequency. The obtained results have enabled the design and construction of a micro-displacement device responsible for the fine tuning of the coil, through the displacement of a tuning element.The tuned coil and micro-device have been implemented in a 4.7 T MRI. Sample images were obtained and validated, showing the relevance and feasibility of using an auto-tuning resonant system, dedicated to high sensitivity MRI
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Lambert, Simon. "Modélisation, réalisation et caractérisation d'antennes supraconductrices pour la micro-IRM du cerveau de souris à 4,7 T." Phd thesis, Université Paris Sud - Paris XI, 2011. http://tel.archives-ouvertes.fr/tel-00786468.
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En IRM haute résolution du petit animal, un rapport signal sur bruit (RSB) convenable demande habituellement l'utilisation d'un champ magnétique statique beaucoup plus élevé, (jusqu'à 20 T) que pour les applications cliniques quotidiennes (1,5 et 3 T). Une alternative est offerte avec le développement récent d'antennes miniatures en matériau supraconducteur à haute température critique (HTS). Cependant de nombreux problèmes liés à ce type d'antennes subsistent et limitent leur diffusion à grande échelle. Le présent manuscrit présente le développement théorique et expérimental d'une antenne de surface HTS de très petite dimension destinée à l'imagerie du cerveau de souris in vivo à 4,7 T.La première partie traite de la modélisation électromagnétique 3D, à l'aide d'un logiciel commercial (CST-Microwave Studio), de structures monolithiques auto-résonantes adaptées à l'obtention de facteurs de qualité extrêmement élevés (105). Le modèle numérique permet, par rapport à un modèle analytique approché, une meilleure prise en compte de la complexité géométrique de l'antenne et de son environnement cryogénique proche, dont les effets sur les caractéristiques radiofréquences de l'antenne sont considérables.Une deuxième partie présente l'étude des effets du champ statique (de 0 à 4,7 T) et de la température (de 65 à 83 K) sur les caractéristiques électriques d'une antenne HTS, dans le domaine de fréquences de l'IRM pour lequel les propriétés des supraconducteurs ont été peu étudiées jusqu'ici. L'étude montre que les effets délétères du champ sur la sensibilité de l'antenne sont partiellement compensés par une diminution modérée de sa température de fonctionnement. Cette diminution est accessible avec un dispositif original de contrôle de température qui évite de faire appel à un système cryogénique complexe limitant le domaine d'application des antennes HTS.La troisième partie présente les résultats obtenus en imagerie à 4,7 T avec une antenne de surface en matériau HTS dont la taille (diamètre de 6 mm) a été optimisée pour obtenir les meilleures performances en RSB, en vue d'une intégration dans un réseau de 4 antennes. Un RSB 4,5 fois supérieur à celui obtenu avec une antenne en cuivre de même géométrie a été démontré sur fantôme. Ce travail aboutit à la réalisation de la première image de cerveau de souris in-vivo à une valeur de champ supérieure à 3 T avec une antenne HTS. La mise en réseau d'antennes de ce type devrait permettre de couvrir le cerveau de souris complet en imagerie très haute résolution à 4,7 T, avec un RSB comparable à celui qui est accessible aujourd'hui à la limite supérieure de champ magnétique.
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Haywood, Brett. "Advanced gradient coil design for MRI." Thesis, University of Nottingham, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.416422.
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Green, Daniel. "Advanced gradient coil design for MRI." Thesis, University of Nottingham, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.408894.
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Sedlář, Petr. "Návrh a realizace klecové cívky pro MRI." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2016. http://www.nusl.cz/ntk/nusl-242001.
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The work deals with the design and experimental production of the model type Birdcage coil used for magnetic resonance imaging system (MRI). The work deals with the design and behaviour of the model type Birdcage coil volume designed for imaging system for magnetic resonance imaging (MRI). Volume coils are generally very useful for use in MRI, because in transversal design allow easy access into the cavity when the flow vector of magnetization. The aim of the work was to construct a numerical model of transversal coil type Birdcage of the predefined dimensions. The created the coil tuned the desired resonant frequency having regard to maximize performance in the measured sample migrated. The modeling coil experimentally produced and measurements also confirm the accuracy of the numerical model.
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Wei, Juan. "Coil array optimization and wireless transceiver design for MRI." Click to view the E-thesis via HKUTO, 2007. http://sunzi.lib.hku.hk/hkuto/record/B38583021.
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Wei, Juan, and 魏娟. "Coil array optimization and wireless transceiver design for MRI." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2007. http://hub.hku.hk/bib/B38583021.
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Lattanzi, Riccardo. "Radiofrequency detector coil performance maps for parallel MRI applications." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/36187.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.<br>Includes bibliographical references (p. 67-70).<br>Parallel MRI techniques allow acceleration of MR imaging beyond traditional speed limits. In parallel MRI, arrays of radiofrequency (RF) detector coil arrays are used to perform some degree of spatial encoding which complements traditional encoding using magnetic field gradients. As the acceleration factor increases, coil design becomes critical to the overall image quality. The quality of a design is commonly judged on how it compares with other coil configurations. A procedure to evaluate the absolute performance of RF coil arrays is proposed. Electromagnetic calculations to compute the ultimate intrinsic signal-to-noise ratio (SNR) available for any physically realizable coil array are shown, and coil performance maps are generated based on the ratio of experimentally measured SNR to this ultimate intrinsic SNR.<br>by Riccardo Lattanzi.<br>S.M.
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Ferrand, Guillaume. "Antennes reseaux pour la transmission parallele en irm a ultra haut champ : conception, réalisation et stratégie de pilotage." Phd thesis, Université Paris Sud - Paris XI, 2011. http://tel.archives-ouvertes.fr/tel-00647901.
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Le projet Iseult-Inumac mené au sein d'un consortium franco-allemand vise à développer les techniques associées à l'imagerie par résonance magnétique à ultra haut champ, notamment à travers la construction d'un imageur à 11,7 teslas. La résolution accrue du nouvel imageur devrait apporter une meilleure compréhension du système nerveux et de ses dysfonctionnements pour aboutir à un dépistage plus précoce des pathologies telles que la maladie d'Alzheimer, les accidents vasculaires cérébraux ou les tumeurs.La principale difficulté technique du projet, en dehors de la construction de l'aimant statique, réside dans la capacité d'émettre une onde électromagnétique d'amplitude uniforme dans tout le cerveau du patient : problème de l'inhomogénéité de B1 (ou radiofréquence). Une solution proposée consiste à utiliser une antenne réseau à transmission parallèle et des séquences d'excitation IRM spécifiques dites de compensation.Cette thèse se concentre sur la conception des antennes réseaux à transmission parallèle pour l'IRM à 7 et 11,7 T. Un prototype à 8 canaux indépendants utilisant une technologie innovante de résonateurs linéaires est présentée pour l'IRM 7 T. Il a été conçu par la simulation numérique. Un protocole de validation a été développé pour la caractérisation et l'analyse des performances des antennes réseaux. Le succès de cette validation a permis de développer par la simulation une nouvelle antenne à 12 canaux et une stratégie de pilotage innovante permettant de n'utiliser que 8 chaînes de pilotage au lieu de 12. Enfin, la même méthodologie a été appliquée pour concevoir et prédire les performances d'une antenne réseau à 11,7 T.
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Cheng, Man-chun Frederick, and 鄭文俊. "High temperature superconductor tape RF volume coil for MRI systems." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2004. http://hub.hku.hk/bib/B29699848.
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周美嬋 and Mei-sim Chow. "Design of high temperature superconducting Helmholtz coil for MRI system." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2001. http://hub.hku.hk/bib/B31225883.
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Chow, Mei-sim. "Design of high temperature superconducting Helmholtz coil for MRI system /." Hong Kong : University of Hong Kong, 2001. http://sunzi.lib.hku.hk/hkuto/record.jsp?B24367369.
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Saputra, Michael Wijaya. "Water and Fat Image Reconstruction from MRI Raw Multi Coil Data." Thesis, Uppsala universitet, Institutionen för informationsteknologi, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-372138.
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n MRI, water and fat signal separation with robust techniques are often helpful in the diagnosis using MRI. Reliable separation of water and fat will help the doctor to get accurate diagnoses such as the size of a tumour. Moreover, fat images can also help in diagnosing the liver and heart condition. To perform water and fat separation, multiple echoes, i.e. measurements of the raw MR signal at different time points, are required. By utilizing the knowledge of the expected signal evolution, it is possible to perform the separation. A main magnetic field is used in MRI. This field is not perfectly homogeneous. Estimating the non-homogeneities is crucial for correcting the separation signal. This thesis used the method of "Iterative Decomposition of water and fat with Echo Asymmetry and Least-squares estimation" (IDEAL). The aims of the thesis are developed a method which reconstruct fat or water MRI images from raw multi-coil image data and evaluate the method’s accuracy and speed by comparing with an available, implemented reconstruction method. In particular, the stability to so called swap artefacts will be analysed. Estimated field maps or inhomogeneity fields are one important and essential step, but there exist multiple local minima. To avoid choosing the incorrect minima, the initial estimation of the field map had to be close to the actual field map value. Neighbouring pixels would have a similar field map values, since the inhomogeneity field was smoothly varying. As such, we carried out the combination of IDEAL algorithms with a region growing method. We implemented the method to do the water and fat separation from a raw image consisting of multi-coil data and multi- echo. The proposed method was tested and the region growing method shows a significantly improved separation of water and fat, when compared to the traditional method without region growing.
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Chen, Xin. "Analytical Path to Improved RF Field Homogeneity for High Field MRI." Cleveland, Ohio : Case Western Reserve University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=case1237482374.
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Taracila, Victor. "HIGH-FIELD MRI ISSUES: FINITE WAVELENGTH EFFECTS, TRANSVERSE COIL DESIGN AND ACOUSTIC NOISE REDUCTION." online version, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=case1151698057.
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Yilmaz, Ayhan Ozan. "Rf Coil System Design For Mri Applications In Inhomogeneous Main Magnetic Field." Master's thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/12608477/index.pdf.
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In this study, RF coil geometries are designed for MRI applications using inhomogeneous main magnetic fields. The current density distributions that can produce the desired RF magnetic field characteristics are obtained on predefined cubic, cylindrical and planar surfaces and Tikhonov, CGLS, TSVD and Rutisbauer regularization methods are applied to match the desired and generated magnetic fields. The conductor paths, which can produce the current density distribution calculated for each surface selection and regularization technique, are determined using stream functions. The magnetic fields generated by the current distributions are calculated and the error percentages
between the desired and generated magnetic fields are found. Optimum conductor paths that are going to be produced on cubic, cylindrical and planar surfaces and the required regularization method are determined on the basis of error percentages and realizability of the conductor paths.
The optimum conductor path calculated for the planar coil is realized and in the measurement done by LakeShore 3-Channel Gaussmeter, an average error percentage of 11 is obtained between the theoretical and measured magnetic field. The inductance values of the realized RF coil are measured<br>the tuning and matching capacitance values are calculated and the frequency characteristics of the system is tested using Electronic Workbench 5.1. The quality factor value of the tested system is found to be 162.5, which corresponds to a bandwidth of 39,2 KHz at 6,387 MHz (operating frequency of METU MRI system).
The techniques suggested in this study can be used in order to design and realize RF coils on prede¯<br>ned arbitrary surfaces for inhomogeneous main magnetic fields. In addition, a hand held MRI device can be manufactured which uses a low cost permanent magnet to provide a magnetic field and generates
the required RF field with the designed RF coil using the techniques suggested in this study.
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McKibben, Nicholas Brian. "Robust Coil Combination for bSSFP MRI and the Ordering Problem for Compressed Sensing." BYU ScholarsArchive, 2019. https://scholarsarchive.byu.edu/etd/7596.
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Balanced steady-state free precession (bSSFP) is a fast, SNR-efficient magnetic resonance (MR) imaging sequence suffering from dark banding artifacts due to its off-resonance dependence. These banding artifacts are difficult to mitigate at high field strengths and in the presence of metallic implants. Recent developments in parametric modelling of bSSFP have led to advances in banding removal and parameter estimation using multiple phase-cycled bSSFP. With increasing number of coils in receivers, more storage and processing is required. Coil combination is used to reduce dimensionality of these datasets which otherwise might be prohibitively large or computationally intractable for clinical applications. However, our recent work demonstrates that some combination methods are problematic in conjunction with elliptical phase-cycled bSSFP.This thesis will present a method for phase estimation of coil-combined multiple phase-cycled bSSFP to reduce storage and computational requirements for elliptical models. This method is general and works across many coil combination techniques popular in MR reconstruction including the geometric coil combine and adaptive coil combine algorithms. A viable phase estimate for the sum-of-squares is also demonstrated for computationally efficient dimension reduction. Simulations, phantom experiments, and in vivo MR imaging is performed to validate the proposed phase estimates.Compressed sensing (CS) is an increasingly important acquisition and reconstruction framework. CS MR allows for reconstruction of datasets sampled well-under the Nyquist rate and its application is natural in MR where images are often sparse under common linear transforms. An extension of this framework is the ordering problem for CS, first introduced in 2008. Although the assumption is made in CS that images are sparse in some specified transform domain, it might not be maximally sparse. For example, a signal ordered such that it is monotonic is maximally sparse in the finite differences domain. Knowledge of the correct ordering of an image's pixels can lead to much more sparse and powerful regularizers for the CS inverse problem. However, this problem has met with little interest due to the strong dependence on initial image estimates.This thesis will also present an algorithm for estimating the optimal order of a signal such that it is maximally sparse under an arbitrary linear transformation without relying on any prior image estimate. The algorithm is combinatoric in nature and feasible for small signals of interest such as T1 mapping time curves. Proof of concept simulations are performed that validate performance of the algorithm. Computationally feasible modifications for in vivo cardiac T1 mapping are also demonstrated.
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Serano, Peter James. "Design of a Multi-Array Radio-Frequency Coil for Interventional MRI of the Female Breast." Digital WPI, 2009. https://digitalcommons.wpi.edu/etd-theses/747.
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A new method for the simulation of radio frequency (RF) coils has been developed. This method utilizes the FEM simulation package Ansoft HFSS as a base for the modeling of RF coils with complex biological loading effects. The abilities of this software have been augmented with custom MATLAB code to enable the fast prediction of lumped element values needed to properly tune and match the coil structure as well as to perform the necessary post processing of simulation data in order to quickly generate and evaluate field data of the resonating coil and compare design variations. This method was evaluated for accuracy and implemented in the re-design of an existing four channel breast coil array for clinical imaging of the female breasts. Based on the simulation results, a commercially viable printed circuit board (PCB) implementation was developed and tested in a clinical 1.5 T MR scanner. The new design allows for wide open bilateral access to the breast regions in order to accommodate various interventional procedures. The layout has also increased axillary B1 field coverage with minor penalty to the signal-to-noise ratio of the coil array, enabling high-resolution imaging over a wide field-of-view.
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Wong, Yum-wing. "Design and implementation of high temperature superconducting (HTS) tape RF coil and cryostat for MRI applications." Click to view the E-thesis via HKUTO, 2006. http://sunzi.lib.hku.hk/hkuto/record/B37109984.
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Wong, Yum-wing, and 黃鑫榮. "Design and implementation of high temperature superconducting (HTS) tape RF coil and cryostat for MRI applications." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2006. http://hub.hku.hk/bib/B37109984.
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Consalter, Daniel Martelozo. "Implementação de aquisição paralelas de imagens utilizando bobinas de RF tipo phased array e sampled array." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/76/76132/tde-14092017-154855/.
Full textAbstract:
Técnicas de aquisição paralelas e hardware dedicados vem sendo desenvolvidos desde a década de 1980 para reduzir o tempo de aquisição de imagens via ressonância magnética (IRM). Uma bobina do tipo phased array é um dispositivo do tipo receptor, que usa múltiplas bobinas (canais) cada qual com seu próprio circuito de detecção para adquirir simultaneamente os sinais que formam uma imagem ou espectro via IRM. Exemplos de técnica de imagem paralela que usa bobinas tipo phased array são Sensitivy Enconding (SENSE) e GeneRalized Autocalibrating Partial Parallel Acquisition (GRAPPA). Sampled array é o nome de um método proposto neste trabalho em que cada canal de uma bobina multicanal é responsável por adquirir de forma independente o sinal da sua amostra de modo que cada sinal de amostra é endereçado ao seu canal específico. Neste trabalho, descrevemos o desenvolvimento de uma bobina phased array de quatro canais para anatomia de cabeça de rato usando circuito impresso flexível para operar em um sistema de IRM pré-clínico de 2T com objetivo de validar o método de construção e uso de circuito flexível como bobina de recepção. Também desenvolvemos uma bobina de quatro canais para realizar simultaneamente a imagem de quatro sementes na mesma varredura para validar o método Sampled Array com objetivo de melhorar a qualidade da imagem e simultaneamente acelerar experimentos de múltiplas amostras. Os resultados mostram que a bobina de circuito impresso phased array, em comparação com uma bobina de enrolamento de fio regular, forneceu uma boa relação sinal / ruído (RSR) e possui geometria mais adequada à anatomia por ser flexível. Além disso, o processo de fabricação da bobina seja facilitado desde que toda a bobina é construída como um protótipo de circuito impresso. Os bons resultados da bobina sampled array mostraram o método como promissor para imageamento de múltiplas amostras com aumento de RSR e diminuição de tempo de experimentos em relação ao uso de bobinas de canal único.<br>Parallel techniques and dedicated hardware has been developed since the 1980s to reduce acquisition time on Magnetic Resonance Imaging (MRI) scanners. A phased array is a receiver only mode device concept, which uses multiple channels (coils) with their own detection circuits to simultaneously acquire MRI or localized spectroscopic signals. An example of parallel imaging technique that uses phased array coils is Sensitivy Enconding (SENSE). Sampled array is the name proposed in this work for a method in which each channel of a multichannel coil is responsible to acquire independently the signal from its sample so that each sample signal is addressed to its specific channel. In this work, we describe the development of a four-channel phased array coil for rat head anatomy using flexible printed circuit board (PCB), to operate on a 2T pre-clinical MRI scanner to validate the construction method and usage of flexible PCB as a receiver coil. We also developed a four-channel sample array coil to simultaneously perform the imaging of four seeds at the same scan, to validate the proposed method to improve image quality at the same time accelerating multiple seed imaging for agriculture studies. The results show that phased array PCB coil as compared to a regular wire winding coil provide good signal-to-noise ratio (SNR) imaging with more adequate geometry to the anatomy by being flexible. In addition, the coil manufacturing process is facilitated since the entire coil is constructed as a PCB prototype. The sample array imaging showed as a promising method for multiple sample increasing SNR and time to do experiments.