Dissertations / Theses: 'High Field MRI'

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Jiang, Lei. "Developments in High Field MRI." Thesis, University of Nottingham, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.491630.

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The technique of magnetic resonance imaging (MRI) is widely used in both structural and functional imaging. This thesis explores some important developments and applications in high field MRI. The work in this thesis has been undertaken by the author except where indicated by reference. Initially, a purpose-built dynamic functional phantom was devised and used for quality control and testing imaging pulse sequences. A multi-echo GEBPI sequence was assessed and the most efficient ways to combine multiecho data taking account of the effect of bandwidth were explored by using this phantom. Subsequently, this multi-echo sequence was applied for T-i mapping of the whole brain and cerebellum with different slice thicknesses and orientations and used for characterization of the physiological noise in the resting-state brain on 3.0 and 7.0 T systems. Furthermore, physiological noise was also investigated by using a spin echo imaging method. The physiological noise in. gradient and spin echo images was compared. The results support the hypothesis that physiological noise has similar origins as the BOLD signal. Contrast-enhanced MR angiography provides accurate information about vascular structure. The field strength dependence of Rl and R2 relaxivities of a blood pool contrast agent (Gadofosveset) was measured ex vivo in human blood. A computer simulation was performed to investigate quantitatively the performance of contrast-to-noise (CNR) ratio of Gadofosveset-enhanced MRA at different field strengths. Finally, highresolution contrast-enhanced MR angiographic imaging was performed on human subjects at 7.0 T. The initial results demonstrate that, despite posHible technical problems, high quality imaging is feasible at 7.0 T. These H)sults also show that the ultra-high field strength has the potential to offer tllgllificant improvements in CNR and spatial resolution.

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Sulikowska, Aleksandra. "Motion correction in high-field MRI." Thesis, University of Nottingham, 2016. http://eprints.nottingham.ac.uk/33674/.

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The work described in this thesis was conducted at the University of Nottingham in the Sir Peter Mansfield Imaging Centre, between September 2011 and 2014. Subject motion in high- resolution magnetic resonance imaging (MRI) is a major source of image artefacts. It is a very complex problem, due to variety of physical motion types, imaging techniques, or k-space trajectories. Many techniques have been proposed over the years to correct images for motion, all looking for the best practical solution in clinical scanning, which would give cost- effective, robust and high accuracy correction, without decreasing patient comfort or prolonging the scan time. Moreover, if the susceptibility induced field changes due to head rotation are large enough, they will compromise motion correction methods. In this work a method for prospective correction of head motion for MR brain imaging at 7 T was proposed. It would employ innovative NMR tracking devices not presented in literature before. The device presented in this thesis is characterized by a high accuracy of position measurements (0.06 ± 0.04 mm), is considered very practical, and stands the chance to be used in routine imaging in the future. This study also investigated the significance of the field changes induced by the susceptibility in human brain due to small head rotations (±10 deg). The size and location of these field changes were characterized, and then the effects of the changes on the image were simulated. The results have shown that the field shift may be as large as |-18.3| Hz/deg. For standard Gradient Echo sequence at 7 T and a typical head movement, the simulated image distortions were on average equal to 0.5%, and not larger than 15% of the brightest voxel. This is not likely to compromise motion correction, but may be significant in some imaging sequences.

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Mougin, Olivier. "Quantitative methods in high field MRI." Thesis, University of Nottingham, 2010. http://eprints.nottingham.ac.uk/11608/.

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The increased signal-to-noise ratio available at high magnetic ﬁeld makes possible the acquisition of clinically useful MR images either at higher resolution or for quantitative methods. The work in this thesis is focused on the development of quantitative imaging methods used to overcome difﬁculties due to high ﬁeld MRI systems (> 3T). The protocols developed and presented here have been tested on various studies aiming at discriminating tissues based on their NMR properties. The quantities of interest in this thesis are the longitudinal relaxation time T1, as well as the magnetization transfer process, particularly the chemical exchange phenomenon involving amide protons which is highlighted particularly well at 7T under speciﬁc conditions. Both quantities (T1 and amide proton transfer) are related to the underlying structure of the tissues in-vivo, especially inside the white matter of the brain. While a standard weighted image at high resolution can provide indices of the extent of the pathology, a robust measure of the NMR properties of brain tissues can detect earlier abnormalities. A method based on a 3D Turbo FLASH readout and measuring reliably the T1 in-vivo for clinical studies at 7T is ﬁrst presented. The other major part of this thesis presents magnetization transfer and chemical exchange phenomena. First a quantitative method is investigated at 7T, leading to a new model for exchange as well as contrast optimization possibility for imaging. Results using those methods are presented and applied in clinical setting, the main focus being to image reliably the brain of both healthy subjects and Multiple Sclerosis patients to look at myelin structures.

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Wharton, Samuel James. "Susceptibility mapping in high field MRI." Thesis, University of Nottingham, 2011. http://eprints.nottingham.ac.uk/13074/.

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Phase images of the human brain acquired using gradient echo based Magnetic Resonance Imaging techniques show excellent contrast at 7T. This contrast is attributed to small variations in magnetic susceptibility that perturb the main magnetic field and thus yield a spatial variation of the NMR frequency. The work described in this thesis is primarily concerned with mapping the distribution of magnetic susceptibility within the human brain using these phase images. The main technical challenges of the project were first to extract accurate field maps based on phase data, and then to solve the ill-posed problem of inverting these field maps to reconstruct susceptibility (ϰ) maps. In initial work, simulations of field shifts based on known ϰ -distributions are compared to field maps acquired in vivo to highlight the non-local relationship between measured field offsets and the underlying susceptibility. These simulations were carried out using a recently derived Fourier method. The bulk of the thesis is then devoted to a detailed study of the process of inverting field maps generated from phase data using the Fourier relationship to yield quantitative 3D ϰ -maps. Unfortunately, the inversion problem is ill-posed and requires careful conditioning, either through rotation of the sample being imaged or through regularisation. A simple k-space threshold is introduced to condition the inversion and the preliminary results of applying this method to brain data from healthy subjects and patients with Parkinson's disease and multiple sclerosis are presented. The results suggest that susceptibility mapping is sensitive to iron deposition and could be a useful tool in investigating the progression of neurodegeneratived diseases. Iterative inversion algorithms, which deal with noise more robustly and allow more sophisticated filtering techniques to be employed, are then presented. These powerful regularisation methods are compared to previously described techniques, and are shown to yield high quality whole-brain ϰ -maps.

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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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Gerardin, Emilie. "Morphometry of the human hippocampus from MRI and conventional MRI high field." Phd thesis, Université Paris Sud - Paris XI, 2012. http://tel.archives-ouvertes.fr/tel-00856589.

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The hippocampus is a gray matter structure in the temporal lobe that plays a key role in memory processes and in many diseases (Alzheimer's disease, epilepsy, depression ...).The development of morphometric models is essential for the study of the functional anatomy and structure alterations associated with different pathologies. The objective of this thesis is to develop and validate methods for morphometry of the hippocampus in two contexts: the study of the external shape of the hippocampus from conventional MRI (1.5T or 3T) with millimeter resolution, and the study of its internal structure from 7T MRI with high spatial resolution. These two settings correspond to the two main parts of the thesis.In the first part, we propose a method for the automatic classification of patients from shape descriptors. This method is based on a spherical harmonic decomposition which is combined with a support vector machine classifier (SVM). The method is evaluated in the context of automatic classification of patients with Alzheimer's disease (AD) patients, mild cognitive impairment (MCI) patients and healthy elderly subjects. It is also compared to other approaches and a more comprehensive validation is available in a population of 509 subjects from the ADNI database. Finally, we present another application of morphometry to study structural alterations associated with the syndrome of Gilles de la Tourette.The second part of the thesis is devoted to the morphometry of the internal structure of the hippocampus from MRI at 7 Tesla. Indeed, the internal structure of the hippocampus is rich and complex but inaccessible to conventional MRI. We first propose an atlas of the internal structure of the hippocampus from postmortem data acquired at 9.4T. Then, we propose to model the Ammon's horn and the subiculum as a skeleton and a local measure thickness. To do this, we introduce a variational method using original Hilbert spaces reproducing kernels. The method is validated on the postmortem atlas and evaluated on in vivo data from healthy subjects and patients with epilepsy acquired at 7T.

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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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De, Vita Enrico. "Development and optimisation of high-field MRI techniques." Thesis, University College London (University of London), 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.408802.

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Shah, Simon Michael. "Magnetisation transfer effects at ultra high field MRI." Thesis, University of Nottingham, 2017. http://eprints.nottingham.ac.uk/39398/.

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Increased signal to noise ratio in ultra high field Magnetic Resonance Imaging (MRI) has allowed the development of quantitative imaging techniques and new contrast mechanisms, such as Chemical Exchange Saturation Transfer (CEST) to be probed. The development of CEST contrast imaging has involved overcoming a number of technical challenges associated with ultra high field MRI. The B1 transmit field was, and still is, a major challenge. Presented in this thesis, the B1 transmit field in regions of low B1 are improved with the use of dielectric pads and a simulation study shows that the overall B1 transmit field homogeneity is significantly improved when multi-transmit slice-selective RF spokes pulse sequences are used. Multiple methods have been developed to quantify the chemical exchange from slow exchanging proton pools seen in CEST contrast imaging. However, magnetisation transfer (MT) from the macromolecular bound pool contaminates current quantification methods, and presented in this thesis is a method whereby the CEST and MT are simultaneously saturated using dual frequency saturation pulses, allowing the CEST contrast in z-spectra to be separated from the MT and to enhance visualisation of the CEST effects. Despite the considerable interest in CEST, only one study has probed the CEST effects in blood, and interestingly high levels of CEST signals can be observed from the superior sagittal sinus. To investigate these effects, z-spectra from ex vivo blood samples considering the effects of oxygenation, haematocrit levels and cell structure were quantified. Quantification shows that the main source of the CEST signals was from the cells within the blood.

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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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Case, Russell. "REDUCING EDDY CURRENTS IN HIGH MAGNETIC FIELD ENVIRONMENTS." Master's thesis, University of Central Florida, 2008. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4305.

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When an electrical conducting volume is placed into the bore of an MRI undergoing an image scan, time varying magnetic gradients induce eddy currents in this conducting material. These eddy currents in turn produce a mechanical torque on this volume. It is the goal of this thesis to produce a computer simulation of eddy currents produced by placing conducting materials inside an MRI bore. The first part of the thesis establishes the physics and principles behind an MRI system along with several applications. Next, this thesis presents an analysis of eddy current effects produced on a conductor placed into an MRI bore. The design and construction of simulated MRI magnetic fields is then presented along with a study of simulated eddy currents in various test conducting volumes of selected materials. Finally, techniques are discussed for reducing eddy currents in these conducting volumes and materials, along with simulation results showing the reduction in the applied eddy current. The findings of this thesis are summarized in the conclusions and recommendations are made for modification and future applications of these techniques and simulations.
M.S.E.E.
School of Electrical Engineering and Computer Science
Engineering and Computer Science
Electrical Engineering MSEE

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Manivannan, Niranchana. "Super Resolution in Ultra High Field MRI - A Comparison." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1293632071.

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Abualait, Turki S. Sabrah. "Investigating basal ganglia function using ultra-high field MRI." Thesis, University of Nottingham, 2012. http://eprints.nottingham.ac.uk/32366/.

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The basal ganglia (BG) are a group of highly interconnected nuclei that are located deep at the base of the cerebral cortex. They participate in multiple neural circuits or 'loops' with cognitive and motor areas of the cerebral cortex. The basal ganglia has primarily been thought to be involved in motor control and learning, but more recently a number of brain imaging studies have shown that the basal ganglia are involved also in cognitive function. The aim of this work is to investigate the role of the basal ganglia in cognitive control and motor learning by examining its involvement in GO/WAIT and GO/NO-GO tasks, and Motor Prediction task, respectively. Ultra-high field (7 Tesla) fMRI is used to provide higher BOLD contrast and thus higher achievable spatial resolution. A dual echo gradient echo EPI method is used to obtain high quality images from both cortical and sub-cortical regions. A common neural basis across different forms of response inhibition using GO/WAIT and GO/NO-GO cognitive paradigms is observed in the experiments of Chapter 4, as well as distinct brain regions involved in withholding and cancelling of motor responses. Using the GO/WAIT cognitive paradigm in Chapter 5 individuals with Tourette syndrome (TS) are compared to age and gender-matched control healthy subjects (CS), and it is shown that TS subjects are unable to recruit critical cortical and sub-cortical nodes that are typically involved in mediating behavioural inhibition. Furthermore, in Chapter 6, the role of the basal ganglia in motor learning is investigated using the Motor Prediction task. The findings show that the basal ganglia and midbrain regions (i.e., habenula) are involved in motor prediction and enhancing the reinforcement learning process. This thesis aims to investigate the basal ganglia function in cognitive and motor tasks, and concludes with suggested further studies to advance our understanding of the role of the basal ganglia nuclei in cognitive function.

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Dixon, Jennifer Elizabeth. "Optimisation of high-field MRI for investigation of multiple sclerosis." Thesis, University of Nottingham, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.523042.

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Kopechek, Jonathan A. "Monte Carlo simulations of magnetic field perturbers in ultra-high field MRI using supercomputers." Connect to resource, 2006. http://hdl.handle.net/1811/6470.

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Thesis (Honors)--Ohio State University, 2006.
Title from first page of PDF file. Document formatted into pages: contains 94 p.; also includes graphics. Includes bibliographical references (p. 93-94) Available online via Ohio State University's Knowledge Bank.

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Liang, Jiachao. "Dynamic Contrast Enhanced Magnetic Resonance Imaging at High and Ultra-high Fields." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1228327344.

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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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Kolment, Nadine. "Towards High-Field MRI Systems: Design Strategy for the TEM Resonator." Thesis, McGill University, 2014. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=121211.

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High-field magnetic resonance imaging (MRI) is a very promising concept as it benefits from a significant improvement in the signal-to-noise ratio (SNR), a measure that directly affects image resolution. However, as the resonant wavelength approaches the dimensions of the object being imaged, the wave propagation effects of the radio frequency (RF) field significantly deteriorate the uniformity of the excitation pattern, thus leading to contrast aberrations and distortions in the resulting image. Recent proof-of-concept studies have shown the merits of parallel transmission techniques in accurately controlling the RF magnetic field whereas novel coil arrangements, such as the TEM resonator, have provided the necessary platform for conducting truly parallel excitations experiments. The purpose of this thesis is to provide a comprehensive study on the design of the TEM resonator by comparing two modelling techniques. The first technique uses multi-conductor transmission line theory to model the coil; the second technique uses the brute-force computational algorithm called finite-difference time-domain (FDTD). The two techniques are compared in terms of the S11 trends observed while varying TEM resonator design parameters such as the capacitor values and the line element geometry. A difference of 15% in the coil response was observed for an MRI system of 3-Tesla field strength. This modelling error increases with resonant frequency and reaches the 40% mark for a high-field MRI system of 7-Tesla field strength. Despite the diverging results for increasing frequency, this study shows that the variation of design parameters in each modelling technique exhibit comparable trends.
L'imagerie par résonance magnétique (IRM) à haut champ est un concept très promettant car elle bénéficie d'une amélioration importante du rapport signal-bruit, une mesure qui affecte directement la résolution de l'image. Cependant, quand la longueur d'onde de résonance se rapproche des dimensions le l'objet sous examination, les effets de propagation d'onde du champ radiofréquence (RF) déteriore de façon significative l'uniformité du motif de champ d'excitation, ainsi menant à des aberrations de contraste et des distortions dans l'image. Des études récentes ont validé le principe de transmission parallèle pour contrôler le champ magnétique RF tandis que de nouveaux arrangements d'antennes, tel que le résonateur TEM, ont permis des expériences avec des transmission réellement en parallèle. Le but de ce mémoir est d'étudier la conception du résonateur TEM en comparant deux techniques de modélisation. La première technique utilise la théorie de ligne de transmission à conducteurs multiples; la deuxième technique utilise un algorithme de calcul par force brute: la méthode des différences finies dans le domaine temporel (FDTD). Les deux techniques sont comparées par rapport aux tendances observées lorsque les paramètres du résonateur TEM, tel que la valeur des condensateurs et la géométrie des lignes microbandes, sont variés. Une différence de 15% dans la réponse de l'antenne a été observé pour un système d'IRM de 3 Tesla. L'erreur de modélisation augmente avec la fréquence de résonance pour atteindre 40% dans un système d'IRM de 7 Tesla. Malgré les résultats divergents, cette étude démontre que la variation des paramètres de l'antenne présente des tendances comparables dans les deux méthodes.

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Poole, Michael Stephen. "Improved equipment and techniques for dynamic shimming in high field MRI." Thesis, University of Nottingham, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.445686.

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von, Morze Cornelius Jan. "Hardware and software developments for high field (≥ 3T) phased array MRI." Diss., Search in ProQuest Dissertations & Theses. UC Only, 2008. 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:3297779.

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Thesis (Ph.D.)--University of California, San Francisco with the University of California, Berkeley, 2008.
Source: Dissertation Abstracts International, Volume: 69-03, Section: B, page: 1770. Adviser: Daniel B. Vigneron.

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Schwarz, Jolanda M. [Verfasser]. "Advanced Image Reconstruction Methods for Ultra-High Field MRI / Jolanda M. Schwarz." Bonn : Universitäts- und Landesbibliothek Bonn, 2020. http://d-nb.info/1218474947/34.

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Vaidya, Manushka. "Steering Electromagnetic Fields in MRI| Investigating Radiofrequency Field Interactions with Endogenous and External Dielectric Materials for Improved Coil Performance at High Field." Thesis, New York University, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10261392.

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Although 1.5 and 3 Tesla (T) magnetic resonance (MR) systems remain the clinical standard, the number of 7 T MR systems has increased over the past decade because of the promise of higher signal-to-noise ratio (SNR), which can translate to images with higher resolution, improved image quality and faster acquisition times. However, there are a number of technical challenges that have prevented exploiting the full potential of ultra-high field (≥ 7 T) MR imaging (MRI), such as the inhomogeneous distribution of the radiofrequency (RF) electromagnetic field and specific energy absorption rate (SAR), which can compromise image quality and patient safety.

To better understand the origin of these issues, we first investigated the dependence of the spatial distribution of the magnetic field associated with a surface RF coil on the operating frequency and electrical properties of the sample. Our results demonstrated that the asymmetries between the transmit (B₁⁺) and receive (B₁^–) circularly polarized components of the magnetic field, which are in part responsible for RF inhomogeneity, depend on the electric conductivity of the sample. On the other hand, when sample conductivity is low, a high relative permittivity can result in an inhomogeneous RF field distribution, due to significant constructive and destructive interference patterns between forward and reflected propagating magnetic field within the sample.

We then investigated the use of high permittivity materials (HPMs) as a method to alter the field distribution and improve transmit and receive coil performance in MRI. We showed that HPM placed at a distance from an RF loop coil can passively shape the field within the sample. Our results showed improvement in transmit and receive sensitivity overlap, extension of coil field-of-view, and enhancement in transmit/receive efficiency. We demonstrated the utility of this concept by employing HPM to improve performance of an existing commercial head coil for the inferior regions of the brain, where the specific coil’s imaging efficiency was inherently poor. Results showed a gain in SNR, while the maximum local and head SAR values remained below the prescribed limits. We showed that increasing coil performance with HPM could improve detection of functional MR activation during a motor-based task for whole brain fMRI.

Finally, to gain an intuitive understanding of how HPM improves coil performance, we investigated how HPM separately affects signal and noise sensitivity to improve SNR. For this purpose, we employed a theoretical model based on dyadic Green’s functions to compare the characteristics of current patterns, i.e. the optimal spatial distribution of coil conductors, that would either maximize SNR (ideal current patterns), maximize signal reception (signal-only optimal current patterns), or minimize sample noise (dark mode current patterns). Our results demonstrated that the presence of a lossless HPM changed the relative balance of signal-only optimal and dark mode current patterns. For a given relative permittivity, increasing the thickness of the HPM altered the magnitude of the currents required to optimize signal sensitivity at the voxel of interest as well as decreased the net electric field in the sample, which is associated, via reciprocity, to the noise received from the sample. Our results also suggested that signal-only current patterns could be used to identify HPM configurations that lead to high SNR gain for RF coil arrays. We anticipate that physical insights from this work could be utilized to build the next generation of high performing RF coils integrated with HPM.

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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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Wang, Chunsheng. "Numerical study of RF magnetic field, specific absorption rate and signal to noise ratio in high field MRI." Click to view the E-thesis via HKUTO, 2006. http://sunzi.lib.hku.hk/hkuto/record/B36887560.

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Wang, Chunsheng, and 汪春生. "Numerical study of RF magnetic field, specific absorption rate and signal to noise ratio in high field MRI." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2006. http://hub.hku.hk/bib/B36887560.

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Mitchell, Chad A. "Besign-directed measurements of B1 heterogeneity and spin-lattice relaxation for 8 Tesla MRI." The Ohio State University, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=osu1095684374.

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Kearney, H. "Investigation of multiple sclerosis spinal cord using high field MRI with multi-transmit technology." Thesis, University College London (University of London), 2014. http://discovery.ucl.ac.uk/1452991/.

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This thesis explores abnormalities in the multiple sclerosis (MS) spinal cord and their relationship with physical disability through the use of conventional and quantitative magnetic resonance imaging (MRI). Firstly, an hypothesis was tested that spinal cord atrophy would be associated with disability, independently from brain atrophy and lesion load, in long disease duration MS. The results presented confirm that cord atrophy is significantly associated with higher levels of physical disability after more than twenty years of MS. Following this observation, the next experiment investigated whether a combination of an active surface model (ASM) and high resolution axial images, would provide a more reproducible measure of spinal cord cross-sectional area; compared to previously described methodologies. The results presented show the superior reproducibility of the ASM combined with axial images for the measurement of cord area in MS, which may be of relevance to future clinical trials utilising cord atrophy as an outcome measure. The pathology of MS in the spinal cord was also explored in several ways using MRI. Firstly, spinal cord lesion morphology was studied, to investigate whether focal lesions, that traversed two or more spinal cord columns and involved the grey matter, would be associated with progressive MS. The results presented confirm this association and also that diffuse abnormalities are more frequently seen in progressive disease. Secondly, spinal cord lesion load was measured quantitatively on axial images, to investigate if this measure would be associated with disability independently from cord atrophy. The functional importance of focal lesions in MS is highlighted by demonstrating an independent association between lesion load and disability. Thirdly, magnetisation transfer ratio (MTR) measures of the outer spinal cord were obtained, in an area expected to contain the pia mater and subpial tissue, to investigate whether outer cord abnormalities could be seen in MS compared to healthy controls and if such abnormalities would be associated with cord atrophy. The results presented show that significant decreases in MTR occur in the outer cord early in the disease course, prior to the development of cord atrophy and further decreases in MTR were seen in progressive MS. Furthermore, an independent association is presented between outer cord MTR and cord atrophy, suggesting that spinal cord meningeal inflammation may be associated with axonal loss in MS. Lastly, diffusion tensor imaging was used in the spinal cord grey matter, in order to investigate whether microstructural abnormalities in this structure would be associated with physical disability. The results of this study identified an association between grey matter radial diffusivity and disability, independently from cord atrophy, suggesting a significant contribution of spinal cord grey matter pathology to clinical dysfunction. In summary, this thesis shows that MS spinal cord abnormalities may be visualised and quantified using high field MRI, and are significantly associated with disability. The observations presented may of relevance to future MRI studies and clinical trials in MS that aim to understand and potentially prevent the pathological processes underlying irreversible physical disability.

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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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Fatahi, Mahsa [Verfasser]. "Ultra-high field MRI bio-effects and safety assessment : a multidisciplinary approach / Mahsa Fatahi." Magdeburg : Universitätsbibliothek, 2017. http://d-nb.info/1139048465/34.

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Burgess, Richard Ely. "Magnetic resonance imaging at ultra high field implications for human neuroimaging /." Connect to this title online, 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1089949841.

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Thesis (Ph. D.)--Ohio State University, 2004.
Title from first page of PDF file. Document formatted into pages; contains xiv, 222 p. : ill. (some col.). Advisor: Pierre-Marie Luc Robitaille, Dept. of Emergency Medicine. Includes bibliographical references.

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Ripoli, Cristina. "Low and high field Magnetic Resonance Imaging and its application in food science and plants." Doctoral thesis, Universita degli studi di Salerno, 2018. http://elea.unisa.it:8080/xmlui/handle/10556/4385.

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2016 - 2017
Nuclear Magnetic Resonance (NMR) and Magnetic Resonance Imaging (MRI) are techniques that have seen a remarkable success and a fast growth over the past decades. Thanks to its non-invasivity and non-descrutivity, the MRI enhances its potential to perform inspections and studies of the internal structure of intact samples such as fruits and vegetables. without modifications caused by the measurements Due to the presence of a high water content in these products, MRI can be useful to obtain information about tissue properties and, thanks to the high sensitivity, can trace water distribution and migration. The characteristic NMR relaxation times are used as parameters for the quantification of water content or for the extraction of information related to changes in microstructure. The idea behind this thesis is the investigation of new methodologies intended to carry out fast and accurate evaluation of moisture content in a food matrix through MRI. At the same time the development of appropriate protocols and analysis tools allowing a simple extraction of those information in a reproducible and reliable way. Two different approaches have been used, both based on data extracted by MR Imaging and a comparison of the two methods is presented. The goal is to exploit MRI as a real measurement instrument with a simple and fast measurement protocol: to achieve this goal we need to identify quantitative MR parameters that provide the most relevant information with respect to the physical quantities we want to measure. To use and validate the MRI as quantitative tool is our major challenge and the results obtained in this thesis keep us confident about the achievement of this goal. This could hopefully open a way for new methods to perform MRI analysis. [edited by Author]
XVI n.s. (XXX ciclo)

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MORE, SHASHIKANT R. "EXPERIMENTAL CHARACTERIZATION AND ACTIVE CONTROL SIMULATION OF THE ACOUSTIC NOISE RESPONSE OF A HIGH-FIELD, HIGH RATE MRI SCANNER." University of Cincinnati / OhioLINK, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1100536748.

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von, Smuda Steffen. "Applicability of Quantitative Functional MRI Techniques for Studies of Brain Function at Ultra-High Magnetic Field." Doctoral thesis, Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-161683.

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This thesis describes the development, implementation and application of various quantitative functional magnetic resonance imaging (fMRI) approaches at ultra-high magnetic field including the assessment with regards to applicability and reproducibility. Functional MRI (fMRI) commonly uses the blood oxygenation level dependent (BOLD) contrast to detect functionally induced changes in the oxy-deoxyhaemoglobin composition of blood which reflect cerebral neural activity. As these blood oxygenation changes do not only occur at the activation site but also downstream in the draining veins, the spatial specificity of the BOLD signal is limited. Therefore, the focus has moved towards more quantitative fMRI approaches such as arterial spin labelling (ASL), vascular space occupancy (VASO) or calibrated fMRI which measure quantifiable physiologically and physically relevant parameters such as cerebral blood flow (CBF), cerebral blood volume (CBV) or cerebral metabolic rate of oxygen (CMRO2), respectively. In this thesis a novel MRI technique was introduced which allowed the simultaneous acquisition of multiple physiological parameters in order to beneficially utilise their spatial and temporal characteristics. The advantages of ultra-high magnetic field were utilised to achieve higher signal-to-noise and contrast-to-noise ratios compared to lower field strengths. This technique was successfully used to study the spatial and temporal characteristics of CBV, CBF and BOLD in the visual cortex. This technique is the first one that allows simultaneous acquisition of CBV, CBF and BOLD weighted fMRI signals in the human brain at 7 Tesla. Additionally, this thesis presented a calibrated fMRI technique which allowed the quantitative estimation of changes in cerebral oxygen metabolism at ultra-high field. CMRO2 reflects the amount of thermodynamic work due to neural activity and is therefore a significant physical measure in neuroscience. The calibrated fMRI approach presented in this thesis was optimised for the use at ultra-high field by adjusting the MRI parameters as well as implementing a specifically designed radio-frequency (RF) pulse. A biophysical model was used to calibrate the fMRI data based on the simultaneous acquisition of BOLD and CBF weighted MRI signals during a gas-breathing challenge. The reproducibility was assessed across multiple brain regions and compared to that of various physiologically relevant parameters. The results indicate that the degree of intra-subject variation for calibrated fMRI is lower than for the classic BOLD contrast or ASL. Consequently, calibrated fMRI is a viable alternative to classic fMRI contrasts with regards to spatial specificity as well as functional reproducibility. This calibrated fMRI approach was also compared to a novel direct calibration technique which relies on complete venous oxygenation saturation during the calibration scan via a gas-breathing challenge. This thesis introduced several reliable quantitative fMRI approaches at 7 Tesla and the results presented are a step forward to the wider application of quantitative fMRI.

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von, Smuda Steffen. "Applicability of Quantitative Functional MRI Techniques for Studies of Brain Function at Ultra-High Magnetic Field." Doctoral thesis, Max-Plank Institut für Kognitions- und Neurowissenschaften, 2014. https://ul.qucosa.de/id/qucosa%3A13196.

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This thesis describes the development, implementation and application of various quantitative functional magnetic resonance imaging (fMRI) approaches at ultra-high magnetic field including the assessment with regards to applicability and reproducibility. Functional MRI (fMRI) commonly uses the blood oxygenation level dependent (BOLD) contrast to detect functionally induced changes in the oxy-deoxyhaemoglobin composition of blood which reflect cerebral neural activity. As these blood oxygenation changes do not only occur at the activation site but also downstream in the draining veins, the spatial specificity of the BOLD signal is limited. Therefore, the focus has moved towards more quantitative fMRI approaches such as arterial spin labelling (ASL), vascular space occupancy (VASO) or calibrated fMRI which measure quantifiable physiologically and physically relevant parameters such as cerebral blood flow (CBF), cerebral blood volume (CBV) or cerebral metabolic rate of oxygen (CMRO2), respectively. In this thesis a novel MRI technique was introduced which allowed the simultaneous acquisition of multiple physiological parameters in order to beneficially utilise their spatial and temporal characteristics. The advantages of ultra-high magnetic field were utilised to achieve higher signal-to-noise and contrast-to-noise ratios compared to lower field strengths. This technique was successfully used to study the spatial and temporal characteristics of CBV, CBF and BOLD in the visual cortex. This technique is the first one that allows simultaneous acquisition of CBV, CBF and BOLD weighted fMRI signals in the human brain at 7 Tesla. Additionally, this thesis presented a calibrated fMRI technique which allowed the quantitative estimation of changes in cerebral oxygen metabolism at ultra-high field. CMRO2 reflects the amount of thermodynamic work due to neural activity and is therefore a significant physical measure in neuroscience. The calibrated fMRI approach presented in this thesis was optimised for the use at ultra-high field by adjusting the MRI parameters as well as implementing a specifically designed radio-frequency (RF) pulse. A biophysical model was used to calibrate the fMRI data based on the simultaneous acquisition of BOLD and CBF weighted MRI signals during a gas-breathing challenge. The reproducibility was assessed across multiple brain regions and compared to that of various physiologically relevant parameters. The results indicate that the degree of intra-subject variation for calibrated fMRI is lower than for the classic BOLD contrast or ASL. Consequently, calibrated fMRI is a viable alternative to classic fMRI contrasts with regards to spatial specificity as well as functional reproducibility. This calibrated fMRI approach was also compared to a novel direct calibration technique which relies on complete venous oxygenation saturation during the calibration scan via a gas-breathing challenge. This thesis introduced several reliable quantitative fMRI approaches at 7 Tesla and the results presented are a step forward to the wider application of quantitative fMRI.:1 Introduction 3 2 Background to Functional Magnetic Resonance Imaging 7 2.1 Magnetic Resonance 7 2.1.1 Quantum Mechanics 7 2.1.2 The Classical Point of View 10 2.1.3 Radio Frequency Pulses 12 2.1.4 Relaxation Effects 13 2.1.5 The Bloch Equations 15 2.2 Magnetic Resonance Imaging 16 2.2.1 Data Acquisition 16 2.2.2 Image Formation 17 2.2.2.1 Slice Selection 17 2.2.2.2 Frequency Encoding 18 2.2.2.3 Phase Encoding 19 2.2.2.4 Mathematics of Image Formation 20 2.2.2.5 Signal Formation 22 2.3 Advanced Imaging Methods 24 2.3.1 Echo-Planar Imaging (EPI) 24 2.3.2 Partial Fourier Acquisition 25 2.3.3 Generalised Autocalibrating Partially Parallel Acquisition (GRAPPA) 25 2.3.4 Inversion Recovery (IR) 26 2.3.5 Adiabatic Inversion 26 2.3.5.1 Hyperbolic Secant (HS) RF pulses 28 2.3.5.2 Time Resampled Frequency Offset Corrected Inversion (tr-FOCI) RF Pulses 28 2.4 Physiological Background 29 2.4.1 Neuronal Activity 30 2.4.2 Energy Metabolism 31 2.4.3 Physiological Changes During Brain Activation 32 2.4.4 The BOLD Contrast 34 2.4.5 Disadvantages of the BOLD Contrast 35 2.5 Arterial Spin Labelling (ASL) 35 2.5.1 Pulsed Arterial Spin Labelling 37 2.5.2 Arterial Spin Labelling at Ultra-High Field 41 2.6 Vascular Space Occupancy (VASO) 42 2.6.1 VASO at Ultra-High Field 44 2.6.2 Slice-Saturation Slab-Inversion (SS-SI) VASO 45 2.7 Calibrated Functional Magnetic Resonance Imaging 47 2.7.1 The Davis Model 47 2.7.2 The Chiarelli Model 50 2.7.3 The Generalised Calibration Model (GCM) 52 3 Materials and Methods 53 3.1 Scanner Setup 53 3.2 Gas Delivery and Physiological Monitoring System 53 3.3 MRI Sequence Developments 55 3.3.1 Tr-FOCI Adiabatic Inversion 55 3.3.2 Optimisation of the PASL FAIR QUIPSSII Sequence Parameters 60 3.3.3 Multi-TE Multi-TI EPI 64 4 Experiment I: Comparison of Direct and Modelled fMRI Calibration 68 4.1 Background Information 68 4.2 Methods 69 4.2.1 Experimental Design 69 4.2.2 Visuo-Motor Task 70 4.2.3 Gas Manipulations 71 4.2.4 Scanning Parameters 71 4.2.5 Data Analysis 72 4.2.6 M-value Modelling 72 4.2.7 Direct M-Value Estimation 73 4.3 Results 74 4.4 Discussion 79 4.4.1 M-value Estimation 79 4.4.2 BOLD Time Courses 82 4.4.3 M-Maps and Single Subject Analysis 82 4.4.4 Effects on CMRO2 Estimation 83 4.4.5 Technical Limitations and Implications for Calibrated fMRI 84 4.5 Conclusion 89 5 Experiment II: Reproducibility of BOLD, ASL and Calibrated fMRI 90 5.1 Background Information 90 5.2 Methods 91 5.2.1 Experimental Design 91 5.2.2 Data Analysis 91 5.2.3 Reproducibility 93 5.2.4 Learning and Habituation Effects 95 5.3 Results 95 5.4 Discussion 101 5.4.1 Breathing Manipulations 102 5.4.2 Functional Reproducibility 107 5.4.3 Habituation Effects on Reproducibility 109 5.4.4 Technical Considerations for Calibrated fMRI 110 5.5 Conclusion 112 6 Experiment III: Simultaneous Acquisition of BOLD, ASL and VASO Signals 113 6.1 Background Information 113 6.2 Methods 114 6.2.1 SS-SI VASO Signal Acquisition 114 6.2.2 ASL and BOLD Signal Acquisition 114 6.2.3 Experimental Design 114 6.2.4 Data Analysis 115 6.3 Results 115 6.4 Discussion 116 6.5 Conclusion 120 7 Conclusion and Outlook 121

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Finnegan, Mary E. "Investigation of the relationship between iron and high field MRI in healthy and Alzheimer's disease tissue." Thesis, University of Warwick, 2013. http://wrap.warwick.ac.uk/60293/.

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It has been proposed that increased tissue iron concentration, which has been observed in certain regions of the brain in individuals with Alzheimer’s Disease (AD), could provide a marker for diagnosis through detection with MRI. This is investigated in this thesis using high field MRI to examine post mortem human brain tissue. It is shown here that by using data from multiple brain regions discriminant analysis can successfully differentiate between AD and control samples, even when no statistically significant differences are observed in individual brain regions. A unique set of complementary techniques was used to investigate iron content, R2 and R2* of tissue samples from the caudate nucleus, putamen, globus pallidus substantia nigra, amygdala and pons, from a set of three control and AD cases. The particulate iron content of the samples was investigated by SQUID magnetometry and was followed by iron quantification. A trend of increased particulate and total iron concentration was observed in the AD tissue compared to control, however this did not reach statistical significance in any brain region. High resolution MRI relaxometry at 9.4 T was carried out on tissue from the caudate nucleus, putamen, globus pallidus and substantia nigra using a custom design Bruker micro-imaging MicWB40 probe. As part of the work towards this PhD the probe was tested, and MRI relaxometry protocols optimised for high resolution (86 x 86 μm in plane, 150 μm slice thickness) mapping of tissue samples with high iron concentration. Again, no statistically significant differences were observed between AD and control tissue. However, discriminant analysis of these data (particulate or total iron or R2 or R2*) from multiple brain regions achieved differentiation between control and AD cases with 100% sensitivity and specificity for this small sample set. This demonstrates the potential clinical usefulness of MRI of measurements of non-haem brain iron to aid in disease diagnosis. Synchrotron X-ray fluorescence (SXRF) mapping of 30 μm thick sections, cut from the MRI samples, showed the relative concentration distribution of iron, copper and zinc in one AD and control sample from each brain region. Each metal was shown to have a distinct distribution. In particular, the inhomogeneity of iron concentration within individual brain regions, such as the putamen, was demonstrated. This may explain the wide variation in iron concentration reported in the literature for the same brain regions, and highlights the importance of close anatomical matching of samples when making comparisons. The ability of high resolution SXRF mapping to investigate the metal content within individual cells was demonstrated and used to show an increase in iron in individual AD neurons, in addition to the surrounding grey and white matter tissue. Spatially matched SXRF and MRI maps were used to demonstrate a strong, statistically significant linear relationship between tissue iron concentration and R2, R2* and R2’ at 9.4 T. The gradient of the linear relationship between iron and R2, agrees extremely well with the predicted gradient at this field, where the prediction was made by Vymazal et al. (1996) using MRI relaxometry at 0.05 to 1.5 T. To the best of my knowledge, this is the first time that this relationship has been quantified at 9.4 T, or at any field above 7 T. MRI at 14.1 T was carried out on low iron concentration regions (the pons and amygdala). Matched SXRF and R2* maps did not show a strong linear relationship between iron and R2*. The iron concentration in these regions is less than 50 μg/g and it was concluded that in tissue with low iron content, other tissue properties - such as water content - are dominating the value of R2*. This result was replicated with data measured at 9.4 T, when only tissue with an iron concentration of less than 50 μg/g was considered.

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Leroi, Lisa. "Quantitative MRI : towards fast and reliable T₁, T₂ and proton density mapping at ultra-high field." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS429/document.

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L’IRM quantitative recouvre l’ensemble des méthodes permettant de mesurer des paramètres physiques accessibles en Résonance Magnétique Nucléaire. Elle offre un bénéfice par rapport à l’imagerie en pondération classiquement utilisée, notamment pour la détection, la caractérisation physiopathologique mais aussi pour le suivi thérapeutique des pathologies. Malgré ce potentiel avéré connu de longue date, ces méthodes restent peu utilisées dans la routine clinique. La raison principale est la longueur des acquisitions par rapport à l’approche classique. Les paramètres physiques que nous souhaitons étudier plus particulièrement sont le temps de relaxation longitudinal (T₁), transversal (T₂), le coefficient de diffusion apparent (ADC), et la densité de protons (DP). Malgré la possibilité d’atteindre une meilleure qualité d’images, ces cartographies in vivo sont quasiment inexistantes dans la littérature au-delà de 3T car leur implémentation nécessite de surmonter un certain nombre de limites spécifiques aux IRM ultra-haut champs (UHF). Au travers de ce projet de thèse, une méthode d’imagerie quantitative basée sur les états de configurations (QuICS) a été implémentée, pour déterminer ces paramètres quantitatifs de façon simultanée sous fortes contraintes propres aux UHF. L’approche a été optimisée dans le but d’obtenir des cartographies fiables et rapides. Le potentiel de la méthode a été démontré dans un premier temps in vitro sur un noyau tel que le sodium démontrant des propriétés complexes à cartographier. Puis dans un second temps, des acquisitions ont été réalisées sur proton, in vivo, en un temps d’acquisition compatible avec une utilisation en routine clinique à 7T. L’application d’une telle méthode d’IRM quantitative à UHF sur des populations permettra d’ouvrir de nouvelles voies d’études pour le futur
Quantitative MRI refers to methods able to measure different physical parameters accessible in Nuclear Magnetic Resonance. It offers benefits compared to weighting imaging commonly used, for the detection, the pathophysiological characterization but also for the therapeutic follow-up of pathologies for example. Despite this long-established potential, these methods remain little used in clinical routine. The main reason is the long acquisition time compared to the classical approach. The physical parameters that we will study more particularly are the longitudinal (T₁), transverse (T₂) relaxation time, the apparent diffusion coefficient (ADC), and the proton density (DP). Despite the possibility to achieve a better image quality, these in vivo mappings are virtually non-existent in the literature beyond 3T because their implementation requires overcom-ing a number of specific ultra-high-field (UHF) MRI limits. Through this thesis project, a Quantitative Imaging method using Configuration States (QuICS) was implemented under strong UHF constraints, to determine these parameters simultaneously. The technique has been optimized to obtain fast and reliable maps. The potential of the method was first demon-strated in vitro on a nucleus such as sodium, exhibiting complex properties. As a second step, acquisitions were performed in proton, in vivo, in an clinically-relevant acquisition time, compatible with a routine use at 7T for population imaging. The application of such a method of quantitative MRI to UHF will open new research possibilities for the future

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Chang, Yu-Chun [Verfasser], and Anke [Akademischer Betreuer] Henning. "Real-time Feedback of B0 Shimming at Ultra High Field MRI / Yu-Chun Chang ; Betreuer: Anke Henning." Tübingen : Universitätsbibliothek Tübingen, 2018. http://d-nb.info/116880390X/34.

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Fiege, Daniel Pascal [Verfasser]. "Development and application of multiple-quantum coherence techniques for in vivo sodium MRI at high and ultra-high field strengths / Daniel Pascal Fiege." Aachen : Hochschulbibliothek der Rheinisch-Westfälischen Technischen Hochschule Aachen, 2014. http://d-nb.info/1052254756/34.

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Fuhrer, Erwin [Verfasser], and J. G. [Akademischer Betreuer] Korvink. "Advanced interfaces for biomedical engineering applications in high- and low field NMR/MRI / Erwin Fuhrer ; Betreuer: J. G. Korvink." Karlsruhe : KIT-Bibliothek, 2019. http://d-nb.info/1195049161/34.

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He, Yi [Verfasser], and Xin [Akademischer Betreuer] Yu. "High-Field Functional MRI from the Perspective of Single Vessels in Rats and Humans / Yi He ; Betreuer: Xin Yu." Tübingen : Universitätsbibliothek Tübingen, 2020. http://d-nb.info/1210484307/34.

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Al, Mohamad Zakriya Ali E. "Quantitative assessment of the biochemical composition of equine cartilage using 7T ultra-high field magnetic resonance imaging (MRI) techniques." Thesis, University of Glasgow, 2016. http://theses.gla.ac.uk/8227/.

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Equine fetlock region disease is responsible for significant morbidity and mortality. Diagnosis of sesamoidean ligament, cartilage and subchondral bone injury has been obtained by clinical MRI. Low-field MRI provides images helpful in the investigation of MCPJ/MTPJ region pathology in horses in the clinical setting but the greater resolution of high and ultra-field MR images has the potential to aid interpretation through a better understanding of MRI anatomy. Quantitative MRI could provide a non-invasive technique to determine tissue biochemical properties associated with the early onset of articular cartilage degenerative conditions such as osteoarthritis. So far, ultra-high field MRI has not been used in equine research and practice. However, recently 3T MRI has been introduced in equine hospitals in Europe and the US. The general objectives of this project, which utilised cadaver limbs, was to improve understanding of the MRI anatomy of the equine MCPJ/MTPJ region and to evaluate the use of MRI for the non-invasive, quantitative assessment of articular cartilage from the same region. The first specific objective was to describe the appearance of the normal anatomy of the equine MCPJ/MTPJ region, especially the SDFT & DDFT and DSLs, using high field (1.5T) and ultra high field (7T) MRI and to compare the images obtained with the two systems. The second objective was to determine the accuracy and precision of articular cartilage thickness measurements using 1.5T and 7T MRI and comparing the measurements with those made from histological sections of the MCPJ/MTPJ. The third objective was to measure T1 & T2 MRI sequence relaxation times for normal horse articular cartilage pre and post gadolinium contrast (dGEMRIC) administration and to determine their correlation with GAG concentration, including a description of topographical variation. The fourth objective was to compare sodium concentration in normal equine MCPJ/MTPJ articular cartilage measured using 7T MR imaging with a dual tuned quadrature 23Na/1H coil with the biochemical properties (sodium concentration determined by flame photometry and GAG concentration). The final objective was to evaluate MR sodium imaging for the assessment of enzymatically degraded equine cartilage. The findings demonstrated that 7T MRI produces high resolution images, which enable better evaluation of the hard and soft tissues of the equine MCPJ/MTPJ region than images from lower field MR systems and which permit accurate and precise articular cartilage thickness measurements to be made. Moreover, it was found that the dGEMRIC technique appears to provide a feasible quantitative tool for evaluating the articular cartilage properties. However, the quantitative parameters determined by the dGEMRIC method cannot fully characterise the biochemical properties of the cartilage. Moreover, delayed gadolinium-enhanced (dGEMRIC) techniques are time consuming, requiring relatively long incubation and scanning times. The measurement of T2 time is a very complex method. The work described in the last chapters demonstrated that sodium MRI was significantly correlated with the biochemical properties of the equine articular cartilage. Therefore the sodium MRI technique showed promise in imaging articular cartilage and providing useful information on the biochemical properties of the cartilage.

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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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Geng, Jianzhao. "Flux pumping for high-Tc superconducting (HTS) magnets." Thesis, University of Cambridge, 2017. https://www.repository.cam.ac.uk/handle/1810/268221.

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High Tc superconductors are enabling in the generation of extremely high magnetic fields. Flux pumping is a promising technology which can be used to operate HTS magnets without significant loss. In this decade, several HTS flux pumps based on travelling magnetic waves have been developed, yet their physics is still unclear. This thesis established a framework in the area of flux pumping for HTS coils. It revealed the underlying physics of existing travelling wave flux pumps, which is an important theoretical contribution. Based on the thorough understanding of flux pumping mechanism, the author proposed two novel types of flux pumps. The new inventions make flux pumping much easier, more controllable, and much less energy consuming. These flux pumps may promote the future applications of HTS magnets. This thesis can be a guidebook for researchers and engineers in developing flux pumps.

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MILESI, GLORIA. "Temporal lobe epilepsy: a combined study with high field (7T) Magnetic Resonance Imaging and optical and ultrastructural histopathology." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2014. http://hdl.handle.net/10281/80943.

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Temporal lobe epilepsy (TLE) is the most common form of focal epilepsy with 60-75% of cases reported in surgical series. The hippocampus is involved in the genesis of the seizures and hippocampal sclerosis (HS) is the most frequent neuropathological finding observed in surgical samples. However extra-hippocampal neocortical structures may also be involved and the focal cortical dysplasia (FCD) is the most common second alteration frequently associated with HS. Aim of this project was to clarify, both at radiological and neuropathological level, the abnormalities frequently observed in the temporal pole of many TLE patients as the focal cortical dysplasia, the hippocampal sclerosis and the radiological alteration of grey/white matter boundary called “blurring”. The study was performed on surgical specimens of human temporal cortices and hippocampi from TLE patients and autoptic hippocampi at different stage of development submitted first to high resolution (7T) MRI and then processed for histological analysis. Comparison between 7T MRI data with corresponding histological and immunohistochemical features was done. The first part of this study demonstrates that thanks to differences in MRI signal intensities, depending on different density and distribution of cells and myelin fibres, high-resolution ex-vivo MRI enables to visualize the intracortical organization in normal and pathological areas and can detect the subtle architectural alterations in samples presenting dysplastic cortex. The temporo-polar blurring has demonstrated to be due to a great degeneration of fibre bundles in the white matter and, since the age at epilepsy onset is earlier in patients with blurring in comparison to those without blurring, these data suggest that it consists in a slowly evolving chronic degeneration process with the redistribution of the remaining fibres. The comparative imaging-histology investigation on healthy hippocampal specimens shows that 7T MRI can identify the main anatomical structures and the sublayers of the normal hippocampus along its anterior-posterior axis. In sclerotic surgical hippocampi high resolution MRI reveals areas of anomalous hyperintensity of signal associated to marked loss of neurons and intense gliosis as visualized by histological analysis for neuronal and glial cells. Moreover the investigation of intrahippocampal projections performed using fractional anisotropy and fiber tracking, demonstrates a disorganization of fibers in sclerotic samples in comparison to normal hippocampi. The same experimental protocol applied to healthy autoptic hippocampi at different stage of development reveals that during fetal period the MRI signal is related to the cellular density, in fact the regions characterized by densely packed neurons are easily recognizable on ex vivo high field MRI as hypointense areas, while in post-natal specimens the MRI signal is still linked to the cell density but, with the appearance and the progressive increase of the myelin fibers content, this correlation becomes less obvious and the myelin represent the histological component which mainly contributes on MRI signal intensity. This study shows the potential utility of ex-vivo high-field MRI in the understanding of temporal cortical and hippocampal abnormalities, included developmental hippocampal changes, and suggests its possible application in vivo in the near future for the study of several disorders.

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Spicher, Nicolai [Verfasser], and Mark E. [Akademischer Betreuer] Ladd. "Time-frequency analysis of optical and electrical cardiac signals with applications in ultra-high-field MRI / Nicolai Spicher ; Betreuer: Mark E. Ladd." Duisburg, 2020. http://d-nb.info/1221061801/34.

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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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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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Huang, Fangping. "Water and Fat Image Reconstruction in Magnetic Resonance Imaging." Case Western Reserve University School of Graduate Studies / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=case1309791802.

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Sharma, Puneet. "Comparison of Delayed Contrast-Enhanced Magnetic Resonance Imaging of Myocardial Viability at 1.5 and 3 Tesla." Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/6911.

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Imaging of myocardial viability using the delayed enhancement technique currently provides high image contrast between infarcted and normal tissue with the aid of a magnetization prepared fast gradient echo pulse sequence following the administration of an extracellular contrast agent. However, there exists a degree of image contrast variability and subjectivity due to contrast agent kinetics and user-specified imaging parameters. Also, the technique has not been explored at higher field strengths (3T), which offer greater inherent signal-to-noise ratio. The overall goal of this study is to compare magnetic resonance delayed contrast enhancement of myocardial infarction at 1.5T and 3T. The analysis was conducted by first developing a comprehensive mathematical simulation of the imaging sequence, which allowed modification of various imaging parameters. Simulations were performed to optimize the sequence for flip angle and inversion time, as well as to evaluate the influence of other image parameters that affected contrast. These theoretical results were validated experimentally with phantoms. In vivo post-contrast T1 measurements at 1.5T and 3T from normal volunteers (n=10) and patients (n=5) provided more precise input into mathematical optimization simulations. In both populations, longer T1 values were found at 3T compared to 1.5T for normal (pre-contrast: 1.24 .06s vs. 1.07 .05s; post-contrast: 0.34-0.59 vs. 0.33-0.54s, n=15) and infarcted myocardium (pre-contrast: 1.27 .06s vs. 1.04 .06s; post-contrast: 0.25-0.37s vs. 0.23-0.32s, n=5). Corresponding simulations using these T1 values revealed an infarct-to-normal tissue contrast gain at 3T of approximately 25%. In vivo image contrast between infarcted and normal tissue following contrast administration was also higher at 3T by approximately 37%. In conclusion, there was good correlation between mathematical simulations of delayed enhancement and experimental results, enabling parameters to be compared and optimized offline given input T1 values. Although contrast-enhanced viability imaging at 3T suffered from artifacts due to field, RF, and inversion pulse inhomogeneity, these results suggest that 3T offers higher contrast-to-noise ratio than 1.5T for this application.

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Dissertations / Theses on the topic 'High Field MRI'

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