Dissertations / Theses on the topic 'MRI'
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1
Peterson, Erika. "Synthetic MRI for visualization of quantitative MRI." Thesis, Linköpings universitet, Avdelningen för radiologiska vetenskaper, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-102651.
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Magnetic resonance imaging (MRI) is an imaging technique that is used in hospitals worldwide. The images are acquired through the use of an MRI scanner and the clinical information is provided through the image contrast, which is based on the magnetic properties in biological tissue. By altering the scanner settings, images with different contrast properties can be obtained. Conventional MRI is a qualitative imaging technique and no absolute measurements are performed. At Center for Medical Imaging and Visualization (CMIV) researchers are developing a new MRI technique named synthetic MRI (SyMRI). SyMRI is based on quantitative measurements of data and absolute values of the magnetic properties of the biological tissue can be obtained. The purpose of this master thesis has been to take the development of SyMRI a step further by developing and implementing a visualization studio for SyMRI imaging of the human brain. The software, SyMRI Brain Studio, is intended to be used in clinical routine. Input from radiologists was used to evaluate the imaging technique and the software. Additionally, the requirements of the radiologists were converted into technical specifications for the imaging technique and SyMRI Brain Studio. Additionally, validation of the potential in terms of replacing conventional MRI with SyMRI Brain Studio was performed. The work resulted in visualization software that provides a solid formation for the future development of SyMRI Brain Studio into a clinical tool that can be used for validation and research purposes. A list of suggestions for the future developments is also presented. Future clinical evaluation, technical improvements and research are required in order to estimate the potential of SyMRI and to introduce the technique as a generally used clinical tool.
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Avdeev, S. "Functional MRI." Thesis, Sumy State University, 2014. http://essuir.sumdu.edu.ua/handle/123456789/45414.
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Medical technology has advanced in recent years. Now one can dissect the body in the finest photos and create three-dimensional models of organs and tissues with the help of scanning technology to find in malfunction and to diagnose diseases.
Nevertheless, a relatively new type of scanning technology called functional magnetic resonance imaging (FMRI) raises this technology one step further. FMRI can not only help to diagnose diseases of the brain, but allows doctors to get into our mental processes to determine the way we think and feel. Functional MRI can detect even if we tell the truth.
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Lustig, Michael. "Sparse MRI /." May be available electronically:, 2008. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.
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King, P. J. "Kinetic studies on the MRI/MRII equilibrium of bovine rhodopsin." Thesis, University of Bristol, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.356301.
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Filos, Jason. "Parallel Transmission MRI." Thesis, Imperial College London, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.516789.
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Kaka, Shwan. "Advanced functional MRI." Thesis, University of Sheffield, 2015. http://etheses.whiterose.ac.uk/9962/.
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Functional Magnetic Resonance Imaging (fMRI) has been widely used to study the responses of the somatosensory cortex, motor cortex and associated neuronal activity in the human cerebral cortex. fMRI is a non-invasive and indirect method for mapping brain activity through measurement of the hemodynamic responses associated with electrical neuronal activity and the neural activity leads directly to changes in blood flow, blood volume and the cerebral metabolic rate of oxygen consumption. Non-invasive neuroimaging technologies such as functional MRI have both advantages, such as good spatial resolution, and disadvantages, such as poor temporal resolution. Some of the disadvantages have been alleviated by incorporating other techniques such as optical spectroscopy or electroencephalography (EEG) which are also non-invasive. All these techniques are sensitive to the vascular response of neuronal activity but in addition we are now investigating the existence of a weak direct electromagnetic effect with advanced fMRI. This neuronal current effect which gives rise to main magnetic field modulation should provide additional information for studying nerve characteristics. In this thesis, methods for fMRI mapping of responses from phantoms, the median nerve, the visual system, the motor sensory cortex and the thalamus are optimised and subsequently quantified. The experimental results strongly support the main hypothesis of the thesis and suggest that the generated magnetic field due to ionic current can be detected by present generation MRI using specific experimental designs and stimulation paradigms. Overall our results show that ionic currents in subjects can generate percentage signal changes in MRI up to 0.1± 0.01% corresponding to mean magnetic axonal fields of 0.7± 0.1nT with a Signal to Noise Ratio (SNR) of 3:1. The responses of the median nerve, motor sensory cortex and thalamus were detected using transcutaneous electrical nerve stimulation (TENS) and the visual cortex using strobe light stimulation in the range of frequencies 2.1 Hz to 4.1 Hz. All these measurements were acquired at 1.5T. Fast fMRI experiments using TENS and finger tapping were also acquired simultaneously. In addition, real and imaginary finger tapping experiments were performed in the motor sensory cortex at 3T. Our results imply that axonal fields that are generated due to action potentials can generate effects on MRI sensitive enough to directly detect neuronal activity using advanced fMRI, although sensitivity is still not fully adequate for clinical use.
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Kořínek, Radim. "Rychlé MRI metody." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2010. http://www.nusl.cz/ntk/nusl-218408.
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This thesis deals with comparison of rapid and conventional methods used in MRI (Magnetic Resonance Imaging). There is a description of imaging methods such as EPI (Echo Planar Imaging), Ultra-fast GRE, FSE (Fast spin echo) as well as a snapshot-FLASH and FISP (Fast Imaging with Steady Precession). Experimental part of this thesis deals with the rapid FSE (Fast Spin Echo) method. Especially is explained and assembled an algorithm for proper compilation of data from the FSE method. This algorithm allows us to evaluate the images from the FSE method. This method is examined in detail (in terms of impact parameters) and compared with traditional conventional methods. Finally, the individual images are evaluated, and the best parameters for FSE method are identified.
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Dixon, Emma Charlotte. "Applications of MRI magnetic susceptibility mapping in PET-MRI brain studies." Thesis, University College London (University of London), 2018. http://discovery.ucl.ac.uk/10053515/.
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Magnetic susceptibility mapping (SM) uses magnetic resonance imaging (MRI) phase images to produce maps of the magnetic susceptibility (χ) of tissues. This work focuses on the applications of SM-based imaging to PET-MRI, the hybrid imaging modality which combines positron emission tomography (PET) with MRI. First, the potential of using SM to aid PET attenuation correction (AC) is explored. AC for PET-MRI is challenging as PET-MRI provides no information regarding the electron density of tissues. Recently proposed SM methods for calculating the χ in regions of no MRI signal are used to segment air, bone and soft tissue in order to create AC maps. In the head, SM methods are found to produce inferior air/bone segmentations to high-performing AC methods, but result in more accurate AC than ultrashort-echo (UTE)-based air/bone segmentations, and may be able to provide additional information in subjects with atypical anatomy. Secondly, a SM pipeline for inclusion in a PET-MRI study into biomarkers for Alzheimer’s disease (AD) is developed. In the Insight46 study 500 healthy subjects from the 1946 MRC National Survey of Health and Development are undergoing a comprehensive PET-MRI protocol at two time-points. SM processing methods are compared and optimised, and a method for processing images with oblique imaging planes is developed. The effect of using different tools for automated segmentation of regions of interest (ROIs) on reported regional χ values is analysed. The ROIs resulting from different tools are found to result in large differences in χ values. FIRST is chosen as the most appropriate ROI segmentation tool for this study based on anatomical accuracy as assessed by a neuroradiologist. Initial analysis of χ values from 100 subjects using data from the first time-point is carried out. No significant association with regional χ values is found for amyloid status, PET radiotracer uptake, or APOE genotype.
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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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Zrinzo, L. "MRI guided and MRI verified deep brain stimulation : accuracy, safety and efficacy." Thesis, University College London (University of London), 2011. http://discovery.ucl.ac.uk/1325642/.
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This thesis investigates a systematic approach to the use of MRI-guided and MRI-verified deep brain stimulation (DBS) in clinical practice. The concept of individual targeting of visualised brain structures without microelectrode recording (MER) was examined with respect to accuracy, safety and efficacy. Accurate MRI localisation of the pedunculopontine nucleus, an investigational new DBS target for parkinsonian gait disorders, is described and proof-of-principle confirmed in a cadaver study using MR-microscopy and histological examination. The impact of surgical trajectory on stereotactic accuracy in routine clinical practice was examined at two centres using MER: trajectories involving the ventricle suffered from significantly greater targeting errors compared to those that did not (p<0.001) and multiple brain-passes were more likely to be required to reach the intended target (p<0.01). Subcortical brain shift between pre and postoperative stereotactic images was minimal after MRI-verified procedures without MER (136 procedures); the observed shift did not adversely affect targeting accuracy or clinical outcome. A simple calibration process improved mean targeting errors by 0.6 mm (p<0.001) to 0.9 ± 0.5 mm from the intended target point. A large patient series was compared to a systematic literature review to determine factors associated with haemorrhage; an image-guided and image-verified approach carried a significantly lower risk of haemorrhage and associated permanent deficit than other surgical methodologies (p=0.001). Another study confirmed that, when observing certain precautions, cranial MR images could be obtained with an extremely low risk in patients with implanted DBS hardware. Outcome data from patients undergoing MRI-guided and MRI-verified surgery for Parkinson’s disease and primary generalised dystonia compared favourably to reports from the literature. Mode of anaesthesia did not impact on surgical outcome. In conclusion, this thesis demonstrates that a meticulous approach to MRI-guided and MRIverified DBS is safe and accurate, with clinical outcomes comparable to other techniques.
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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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Rydell, Joakim. "Advanced MRI Data Processing." Doctoral thesis, Linköping : Department of Biomedical Engineering, Linköpings universitet, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-10038.
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Al-Abdul, Salam Amal. "Image quality in MRI." Thesis, University of Exeter, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.288250.
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Bilgic̦, Berkin. "Reconstruction algorithms for MRI." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/79210.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 135-142).
This dissertation presents image reconstruction algorithms for Magnetic Resonance Imaging (MRI) that aims to increase the imaging efficiency. Algorithms that reduce imaging time without sacrificing the image quality and mitigate image artifacts are proposed. The goal of increasing the MR efficiency is investigated across multiple imaging techniques: structural imaging with multiple contrasts preparations, Diffusion Spectrum Imaging (DSI), Chemical Shift Imaging (CSI), and Quantitative Susceptibility Mapping (QSM). The main theme connecting the proposed methods is the utilization of prior knowledge on the reconstructed signal. This prior often presents itself in the form of sparsity with respect to either a prespecified or learned signal transformation.
by Berkin Bilgic.
Ph.D.
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Anblagan, Devasuda. "MRI of foetal development." Thesis, University of Nottingham, 2012. http://eprints.nottingham.ac.uk/30592/.
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Foetal MRI represents a non-invasive imaging technique that allows detailed visualisation of foetus in utero and the maternal structure. This thesis outlines the quantitative imaging techniques used to investigate the effect of maternal diabetes and maternal smoking on foetal development at 1.5 Tesla. The effect of maternal diabetes on placental blood flow and foetal growth was studied. The placental images were acquired using Echo Planar Imaging and blood flow was measured using Intra Voxel Incoherent Motion. The results indicate that peak blood flow in the basal plate and chorionic plate increases across gestation in both normal and diabetic pregnancies. Conversely, diffusion in the whole placenta decreases across gestation, with a more pronounced decrease in diabetic placentae. Following this, a method was developed to use a Tl weighted fat suppressed MRI scan to quantify foetal fat images in-utero. In addition, HAlf Fourier Single-shot Turbo spin Echo (HASTE) and balanced Fast Field Echo (bFFE) were used to acquire images encompassing the whole foetus in three orthogonal planes. These scans were used to measure foetal volume, foetal length and shoulder width. The data shows that foetal fat volume and intra-abdominal fat were increased in foetuses of diabetic mothers at third trimester. The HASTE and bFFE sequences were also used to study the effect of maternal smoking on foetal development. Here, foetal organ volumes, foetal and placental volume, shoulder width and foetal length were measured using a semiautomatic approach based on the concept of edge detection and a stereological method, the Cavalieri technique. The data shows that maternal smoking has significant negative effect on foetal organ growth and foetal growth, predominantly foetal kidney and foetal volume. The work described here certainly has a great potential in non-invasive assessment of abnormal placental function and can be used to study foetal development.
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Semple, Scott I. K. "Clinical cardiac functional MRI." Thesis, University of Aberdeen, 2000. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU602018.
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The purpose of this project was to assess techniques which could be implemented in clinical cardiac MRI using a moderate gradient performance imaging system in order to aid in the assessment of myocardial function. Possible improvements in image contrast were assessed using four different magnetisation preparation schemes applied prior to MR image acquisition in order to aid in the delineation of myocardial borders, and therefore improve cardiac image assessment quality. The usefulness of several novel T2*-weighted acquisition techniques were assessed in clinical cardiac applications in order to indirectly assess myocardial perfusion. Four magnetisation preparation schemes were applied in order to attempt to improve image contrast in short axis gradient-echo cardiac MRI; T2, T1, Magnetisation Transfer Contrast (MTC), and Double Inversion (DI). The T2, and preparation schemes proved to be the most effective, showing an initial improvement in image contrast by approximately 100% and proving effective in improving image contrast over the entire imaging duration {550 ms through the cardiac cycle). The MTC preparation scheme showed a 50% improvement in image contrast, again being effective over the entire imaging duration. The DI preparation scheme proved useful in creating a black blood gradient-echo image but showed no improvement in contrast throughout the imaging duration (since the DI preparation technique is essentially a 'snapshot' technique). Recent developments in cardiac MRI have moved towards assessment of myocardial perfusion, using first-pass contrast-enhancement imaging. This approach requires assessment of a large enough volume of the heart to allow assessment of perfusion as well as retaining a high temporal resolution of 7 or 2 seconds, and therefore a more modem high performance imaging system. For moderate performance gradient MR systems an alternative method of assessing myocardial perfusion is therefore required. Several novel techniques to assess myocardial T2* values in order to indirectly infer myocardial perfusion are introduced. The use of an original multi-echo gradient-echo imaging sequence to acquire T2* pixel-maps was investigated in phantoms and compared with commercially available sequences in order to validate its use.
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Menclík, Tomáš. "3D model z MRI." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2012. http://www.nusl.cz/ntk/nusl-219464.
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The main aim of the thesis is the reconstruction of three-dimensional surface from a~set of two-dimensional images. For the implementation of this application the programming language Java and its extension, that allows work with three-dimensional models, were chosen. First, viewing of three-dimensional models of two different file formats was necessary to allow. To create the three-dimensional models, the Marching Cubes algorithm was used. This algorithm is decribed theoretically in the text, description of the implementation and correction of deficiencies follows. Finally, the implementation of the inversion procedure of reconstruction of the three-dimensional surface, which is the extraction of two-dimensional images from the three-dimensional model, is described.
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Kokkonen, S. M. (Salla-Maarit). "MRI of intracranial tumours in adults:oedema-attenuated inversion recovery MR sequence in low-field MRI, diffusion-weighted MRI and BOLD fMRI." Doctoral thesis, University of Oulu, 2009. http://urn.fi/urn:isbn:9789514292316.
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Abstract
The goal of this study was to explore preoperative evaluation of patients with intracranial tumours using magnetic resonance imaging (MRI) methods: oedema-attenuated inversion recovery (EDAIR) sequence in low-field MRI, and diffusion-weighted imaging (DWI) and resting-state functional MRI (fMRI) in high-field MRI. The aim was also to increase our knowledge about the effects of brain surgery on eloquent brain cortices using new MRI techniques. The total number of patients in these studies was 50 (24 women).
Enhancement of the tumour in ten patients after intravenous administration of gadolinium-based contrast agent in low-field MRI was examined with a new sequence, EDAIR, and compared with more conventionally used partial saturation spin echo sequences. EDAIR may facilitate the perception of small enhancing lesions and is valuable in low-field imaging, where T1-based contrast is inferior to high-field imaging.
DWI was performed on 25 patients in order to evaluate the potential of this imaging method to assist in differential diagnosis of intracranial tumours. It was shown that apparent diffusion coefficient values of the tumour and peritumoural oedema produced by DWI were different in benign and malignant tumours.
Resting-state blood oxygen level-dependent (BOLD) fMRI was performed on eight patients and ten healthy volunteers to examine if functional sensorimotor areas in the brain could be determined without any task-related activations. It was shown that intracranial tumours do not appear to hamper visualization of the sensorimotor area in resting-state BOLD fMRI when independent component analysis is performed, and this method may be used in preoperative imaging when activation studies cannot be performed.
Conventional BOLD fMRI with motor and auditory stimuli was used with seven patients as the effect of brain surgery was studied. The results suggest that resection of a tumour with preoperative oedema probably decreases pressure on the brain and makes the functional cortex transiently more easily detectable in BOLD fMRI.
In conclusion, the MRI imaging methods used in this study can give valuable additional information about the tumour, specifically for preoperative imaging and planning for surgery.
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Nguyen, Huyen Thanh. "Dynamic Contrast-Enhanced MRI and Diffusion-Weighted MRI for the Diagnosis of Bladder Cancer." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1365176629.
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Saikus, Christina Elena. "Towards mri-guided cardiovascular interventions." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/44912.
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Imaging guidance may allow minimally invasive alternatives to open surgical exposure and help reduce procedure risk and morbidity. The inherent vascular and soft-tissue contrast of MRI make it an appealing imaging modality to guide cardiovascular interventional procedures. Advances in real-time MRI have made MRI-guided procedures a realistic possibility. The MR environment, however, introduces additional challenges to the development of compatible, conspicuous and safe devices. The overall goal of this work was to enable selected MRI-guided cardiovascular interventional procedures with clearly visible MR devices. In the first part of this work, we developed actively visualized devices for three distinct MRI-guided interventional procedures and techniques to assess their signal performance. We then investigated factors influencing complex device safety in the MR environment and evaluated a technique to better determine and monitor potential device heating. This input contributed to the development of a system to further improve device safety with continual device monitoring and dynamic scanner feedback control. In the final part of this work, we demonstrated the utility of MRI guidance and actively visualized devices to enable traditional and complex cardiovascular access. Together these provide important elements to bring MRI-guided cardiovascular interventional procedures closer to clinical implementation.
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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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Hulsebos, M. A. Miedema M. F. Oudhoff A. J. "Veiligheid MRI in het UMCG." Groningen : Groningen : HG, Medisch Beeldvormende en Radiotherapeutische Technieken ; Hanzehogeschool Groningen [Host], 2007. http://scripties.hanze.nl/2007/SAGZ/MBRT/17.pdf.
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Scriptie Hanzehogeschool Groningen.Datum laatste controle: 07-09-2007. Samenvatting in het Engels. In opdracht van het Universitair Medisch Centrum Groningen (UMCG), afdeling radiologie. Met lit.opg.
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d'Arcy, James Andrew. "High resolution and rapid MRI." Thesis, Institute of Cancer Research (University Of London), 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.544181.
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Totman, John. "Characterization of PC-MRI data." Thesis, University of Nottingham, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.555502.
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The work in this thesis focuses on the development and implementation of practical approaches to measure and characterise flow data using phase contrast magnetic resonance imaging (PC-MRI), and to use some of the body's natural physiological processes to modulate blood flow with the aim of producing additional probes to study pathologies. The use of low spatial resolution PC-MRI is investigated to allow high sampling rates and near-simultaneous measurement at multiple sites to be performed. The precision of this was validated and used to demonstrate changes in flow provoked by the use of glucose as a probe to alter abdominal blood flow. Waveform analysis to interrogate the phasic temporal flow waveform (PTFW) was also used to further characterise impact of the glucose on normal physiology. Through further experimentation, optimised sequences for the quantification of flow in the much more challenging environment of the right coronary artery (RCA) were implemented. New mathematical models were developed to perform waveform analysis on the RCA unique waveform shape flow data. A Gaussian model proved the most robust model successfully able to model the RCA PTFW with 84% flux and 93% velocity data modelled with over all total residual R2 = 0.68 ± 0.15 flux and R2 = 0.65 ± 0.14 velocity PC-MRI data respectively providing a good fit in all areas except the incisure (the recover period of the wave form after systole and before diastole) and the best overall fit across the entire PTFW. The physiological impact of blood flow during respiratory suspension at defined pressures, as a proxy for inter thoracic pressure, was explored. PC-MR blood flow, and PTFW measurements in the thoracic descending aorta and RCA were assessed for modulation.
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Tyler, Damian J. "Quantitative measurements in obstetric MRI." Thesis, University of Nottingham, 2002. http://eprints.nottingham.ac.uk/13964/.
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This thesis describes the development and application of quantitative echo planar magnetic resonance imaging techniques to the study of human placental development in normal and compromised pregnancies. Initially, a method of rapidly and accurately measuring the transverse relaxation time is proposed using a multi-echo measurement sequence. The method is described, validated on CUS04 phantoms and applied in the study of the human placenta and gastric dilution. It is shown that the inversion provided by sinc pulsesis insufficient to generate an accurate measurement but using adiabatic refocusing pulses yields a measurement that is comparable with a single spin echo. Subsequently, a rapid magnetisation transfer method is presented that allows the quantification of the relative size of the bound proton pool. An experimental pulse sequence is proposed, along with a theoretical model, that permits the investigation of the bound proton pool's transition towards the steady state. The sequence and model are validated using agar gel phantoms and shown to agree well with literature values. When applied in the study of the human placenta, it is shown that there is no significant variation in the fitted value of the bound proton pool size with increasing gestational age or in compromised pregnancies. Finally, several methods of measuring the oxygenation level of blood within the human placenta are investigated. The signal intensities of cardiac gated T~• and T~ weighted images acquired at various points in the maternal cardiac cycle are explored but no significant variation is shown through the cycle. A pulsed gradient spin echo sequence that utilises anti-symmetric sensitising gradients is validated and then applied in the human placenta. Oxygenation measurements with this technique are shown to be unfeasible but the potential of the sequence to monitor blood flow in the placenta is demonstrated.
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Rahman, Hosne Jahan. "MRI studies of polymeric systems." Thesis, University of Kent, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303051.
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Woodhouse, Neil. "Multi-nuclear MRI lung volumetry." Thesis, University of Sheffield, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.434566.
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Korpela, T. (Tuukka). "Mangaanipartikkeleiden käyttö kontrastiaineena MRI-kuvauksessa." Master's thesis, University of Oulu, 2018. http://jultika.oulu.fi/Record/nbnfioulu-201804191493.
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Tiivistelmä. Kantasolujen käyttö sairauksien hoidossa on paljon tutkittu aihe, jolle etsitään koko ajan uusia sovellutuksia. Yksi kehitettävistä sovellutuksista on solujen seuraamisen mahdollistaminen kajoamattomasti kuvantamisella sekä soluterapian antamisen yhteydessä että hoidon seurannan aikana. Magneettikuvaus (MRI) on käyttökelpoinen kuvantamismenetelmä tähän. MRI-kuvaukseen ei liity haitallista ionisoivaa säteilyä ja sillä on myös useita muita etuja toisiin kuvantamismenetelmiin verrattuna, minkä vuoksi sen kehittäminen soluterapian seuraamista varten on hyödyllistä. MRI-kuvausta varten solut voidaan leimata kontrastiaineella niiden havainnoinnin parantamiseksi. Uusia MRI-solukuvauksen kontrastiaineita etsitään koko ajan. Mangaanioksidi on uusi ja yksi lupaavimmista kehitetyistä kontrastiaineista.
Tässä tutkimuksessa pyrittiin saamaan lisätietoa mangaanioksidin toksisuudesta ihmisen kantasolujen leimaamisessa. Tutkimuksessa tutkittiin kahta erilaista mangaanioksidista valmistettua partikkelia. Tavoitteena oli selvittää, miten ihmisen kantasolut selviävät 3 ja 5 viikkoa mangaanioksidilla leimaamisen jälkeen. Saatujen tulosten perusteella solujen elinvoimaisuus ja erilaistumiskyky säilyivät molempien ajanjaksojen ajan.
Tutkimuksessa selvitettiin myös miten eri leima-ainekonsentraatioilla leimatut solut erottuvat MRI-solukuvauksessa eli minkälainen kontrasti leimaamisella saadaan aikaiseksi. Havaittiin, että jo hyvin pienetkin leima-ainekonsentraatiot saavat aikaan merkittävän kontrastin paranemisen.
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Ségonne, Florent 1976. "Unsupervised skull stripping in MRI." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/87823.
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Gountouna, Viktoria-Eleni. "Multicentre structural and functional MRI." Thesis, University of Edinburgh, 2014. http://hdl.handle.net/1842/9536.
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Neuroimaging techniques are likely to continue to improve our understanding of the brain in health and disease, but studies tend to be small, based in one imaging centre and of uncertain generalisability. Multicentre imaging studies therefore have great appeal but it is not yet clear under which circumstances data from different scanners can be combined. The successful harmonisation of multiple Magnetic Resonance Imaging (MRI) machines will increase study power, flexibility and generalisability. I have conducted a detailed study of the performance of three research MRI scanners in Scotland under the name CaliBrain, with the aims of developing reliable, valid image acquisition and analysis techniques that will facilitate multicentre MRI studies in Scotland and beyond. Fourteen healthy volunteers had two brain scans on each of three 1.5T MRI research machines in Aberdeen, Edinburgh and Glasgow. The scans usually took place 2-3 weeks apart. Each scan was performed using an identical scanning protocol consisting of a detailed structural MRI (sMRI) and a range of functional MRI (fMRI) paradigms. The quality assurance (QA) of scanner performance was monitored in all three sites over the duration of the study using a three-part protocol comprising a baseline assessment, regular measures and session specific measures. The analyses have demonstrated that the data are comparable but also that within- and between-scanner variances are evident and that harmonisation work could enhance the level of agreement. The QA data suggest that scanner performance was similar between and within machines over the course of the study. For the structural MRI scans an optimised methodology was utilised to minimise variation in brain geometry between scanners and fit all the scanned brains into a common stereotactic space, such that repeated measures analyses yielded no significant differences over time for any of the three scanners. I examined the reproducibility of the fMRI motor task within and between the three sites. Similar results were obtained in all analyses; areas consistently activated by the task include the premotor, primary motor and supplementary motor areas, the striatum and the cerebellum. Reproducibility of statistical parametric maps was evaluated within and between sites comparing the activation extent and spatial agreement of maps at both the subject and the group level. The results were within the range reported by studies examining the reproducibility of similar tasks on one scanner and reproducibility was found to be comparable within and between sites, with between site comparisons often exceeding the within site measures. A components of variance analysis showed a relatively small contribution of the factor site with subject being the main source of variation. Similar results were obtained for the working memory task. The analysis of the emotional face processing task showed poor reproducibility both within and between sites. These findings suggest that multicentre structural and functional MRI studies are feasible, at least on similar machines, when a consistent protocol is followed in all participating scanning sites, a suitable fMRI task is employed and appropriate analysis methods are used.
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Sedláčková, Gabriela. "Optimalizace MRI měření slepičích embryí." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2015. http://www.nusl.cz/ntk/nusl-221370.
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This thesis deals with optimization of MRI measuring of phantoms containing the chicken embryo. The theoretical part of thesis is dedicated to the MRI fundamentals and description of pulse sequences. In the next part the options of keeping and monitoring the temperature are being discussed. The thesis also deals with design and realization of phantoms which are used for measuring. A browser of images captured by MRI was programmed in Matlab environment. The program allows users to look through the images with different settings of pulses sequences or kind of phantom. The final part of thesis describes the anatomical structures of chicken embryo and discussion of collected results.
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Cui, Xuelin. "Joint CT-MRI Image Reconstruction." Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/86177.
Full textAbstract:
Modern clinical diagnoses and treatments have been increasingly reliant on medical imaging
techniques. In return, medical images are required to provide more accurate and detailed
information than ever. Aside from the evolution of hardware and software, multimodal
imaging techniques offer a promising solution to produce higher quality images by fusing
medical images from different modalities. This strategy utilizes more structural and/or
functional image information, thereby allowing clinical results to be more comprehensive
and better interpreted.
Since their inception, multimodal imaging techniques have received a great deal of attention
for achieving enhanced imaging performance. In this work, a novel joint reconstruction
framework using sparse computed tomography (CT) and magnetic resonance imaging (MRI)
data is developed and evaluated. The method proposed in this study is part of the planned
joint CT-MRI system which assembles CT and MRI subsystems into a single entity. The
CT and MRI images are synchronously acquired and registered from the hybrid CT-MRI
platform. However, since their image data are highly undersampled, analytical methods, such
as filtered backprojection, are unable to generate images of sufficient quality. To overcome
this drawback, we resort to compressed sensing techniques, which employ sparse priors that
result from an application of L1-norm minimization.
To utilize multimodal information, a projection distance is introduced and is tuned to tailor
the texture and pattern of final images. Specifically CT and MRI images are alternately
reconstructed using the updated multimodal results that are calculated at the latest step
of the iterative optimization algorithm. This method exploits the structural similarities
shared by the CT and MRI images to achieve better reconstruction quality. The improved
performance of the proposed approach is demonstrated using a pair of undersampled CT-MRI
body images and a pair of undersampled CT-MRI head images. These images are
tested using joint reconstruction, analytical reconstruction, and independent reconstruction
without using multimodal imaging information. Results show that the proposed method
improves about 5dB in signal-to-noise ratio (SNR) and nearly 10% in structural similarity
measurements compared to independent reconstruction methods. It offers a similar quality
as fully sampled analytical reconstruction, yet requires as few as 25 projections for CT and
a 30% sampling rate for MRI. It is concluded that structural similarities and correlations
residing in images from different modalities are useful to mutually promote the quality of
image reconstruction.Ph. D.
Medical imaging techniques play a central role in modern clinical diagnoses and treatments. Consequently, there is a constant demand to increase the overall quality of medical images. Since their inception, multimodal imaging techniques have received a great deal of attention for achieving enhanced imaging performance. Multimodal imaging techniques can provide more detailed diagnostic information by fusing medical images from different imaging modalities, thereby allowing clinical results to be more comprehensive to improve clinical interpretation. A new form of multimodal imaging technique, which combines the imaging procedures of computed tomography (CT) and magnetic resonance imaging (MRI), is known as the “omnitomography.” Both computed tomography and magnetic resonance imaging are the most commonly used medical imaging techniques today and their intrinsic properties are complementary. For example, computed tomography performs well for bones whereas the magnetic resonance imaging excels at contrasting soft tissues. Therefore, a multimodal imaging system built upon the fusion of these two modalities can potentially bring much more information to improve clinical diagnoses. However, the planned omni-tomography systems face enormous challenges, such as the limited ability to perform image reconstruction due to mechanical and hardware restrictions that result in significant undersampling of the raw data. Image reconstruction is a procedure required by both computed tomography and magnetic resonance imaging to convert raw data into final images. A general condition required to produce a decent quality of an image is that the number of samples of raw data must be sufficient and abundant. Therefore, undersampling on the omni-tomography system can cause significant degradation of the image quality or artifacts after image reconstruction. To overcome this drawback, we resort to compressed sensing techniques, which exploit the sparsity of the medical images, to perform iterative based image reconstruction for both computed tomography and magnetic resonance imaging. The sparsity of the images is found by applying sparse transform such as discrete gradient transform or wavelet transform in the image domain. With the sparsity and undersampled raw data, an iterative algorithm can largely compensate for the data inadequacy problem and it can reconstruct the final images from the undersampled raw data with minimal loss of quality. In addition, a novel “projection distance” is created to perform a joint reconstruction which further promotes the quality of the reconstructed images. Specifically, the projection distance exploits the structural similarities shared between the image of computed tomography and magnetic resonance imaging such that the insufficiency of raw data caused by undersampling is further accounted for. The improved performance of the proposed approach is demonstrated using a pair of undersampled body images and a pair of undersampled head images, each of which consists of an image of computed tomography and its magnetic resonance imaging counterpart. These images are tested using the proposed joint reconstruction method in this work, the conventional reconstructions such as filtered backprojection and Fourier transform, and reconstruction strategy without using multimodal imaging information (independent reconstruction). The results from this work show that the proposed method addressed these challenges by significantly improving the image quality from highly undersampled raw data. In particular, it improves about 5dB in signal-to-noise ratio and nearly 10% in structural similarity measurements compared to other methods. It achieves similar image quality by using less than 5% of the X-ray dose for computed tomography and 30% sampling rate for magnetic resonance imaging. It is concluded that, by using compressed sensing techniques and exploiting structural similarities, the planned joint computed tomography and magnetic resonance imaging system can perform imaging outstanding tasks with highly undersampled raw data.
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Kidane, Tesfaye Kebede. "Toward Faster and Quieter MRI." Case Western Reserve University School of Graduate Studies / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=case1118850517.
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Fan, Mingdong. "THREE INITIATIVES ADDRESSING MRI PROBLEMS." Case Western Reserve University School of Graduate Studies / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=case1585863940821908.
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Vitouš, Jiří. "MRI potkanů - kvantifikace T1 myokardu." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2021. http://www.nusl.cz/ntk/nusl-442490.
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This thesis focuses on cardiac imaging and quantification of T1 relaxation time in rat hearts. Its main focus is to investigate available methods for such quantification and their application in the development of quantification tools. The large impact is given to methods of acquisition synchronization, mainly with respect to cardiac motion and breathing using retrospective gating, where the navigator signal is obtained solely from the acquired data, so without any external equipment such as the ECG or respiratory sensors. This paper takes into account situations where steady-state has been reached and also those where it has not, by means of contrast agent injection or by inversion pulses.
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Holliday, Katherine Frances. "Oxygen-enhanced MRI in cancer." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/oxygenenhanced-mri-in-cancer(bf84c0c5-0647-4035-8607-b1d62d940ea9).html.
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Tumour hypoxia is linked to reduced treatment sensitivity and poor outcome. Oxygen-enhanced MRI (OE-MRI) is a novel technique with the potential to non-invasively image hypoxia. It involves the measurement of MR relaxation rate changes caused by changes in oxygenation within blood and tissue. This thesis is focused on the development of OE-MRI and its clinical application in tumours. Two imaging sequences were optimised and then investigated for accuracy and precision in measuring oxygen enhanced R1 changes. Following that, R1, R2* and blood flow were measured during air and oxygen breathing in healthy kidneys. This study included the implementation of model-driven registration for inversion prepared OE-MRI images. Next, a biophysical model was used to simulate expected ΔR1 in tumour tissue during hyperoxia for a range of underlying physiological conditions. Finally, OE-MRI was applied alongside BOLD and DCE-MRI in clinical studies in renal and cervical tumours. It was shown that a dynamic inversion-prepared HASTE sequence in combination with a baseline T1 map offered the most precise measure of oxygen-enhanced ΔR1. No consistent significant change was found in either T1, R2* or blood flow when using static measures, but significant changes in R1 were found by using dynamicT1-weighted signal. Image registration had variable effect on dynamic signal curves, but reduced errors in T1 calculations. Modelling showed that differences in ΔR1 are mainly caused by the interplay between blood flow, oxygen consumption and capillary length. Finally, clinical studies demonstrated the feasibility of OE-MRI in tumours. The work in this thesis represents an improvement of OE-MRI methodology and offers a new insight into how results from OE-MRI relate to both underlying tumour physiology and other imaging modalities.
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Yanez, Lopez Maria. "Detecting neuroinflammation with molecular MRI." Thesis, University of Nottingham, 2015. http://eprints.nottingham.ac.uk/30599/.
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The work in this thesis is focused on the study of neuroinflammation with molecular magnetic resonance imaging (MRI) methods. Neuroinflammation is a response of the central nervous system to pathological insult and it is present in many neurological disorders, such as Alzheimer’s disease. Being able to image neuroinflammation non-invasively with MRI techniques would have an important clinical value for diagnosis and assessment of therapy effectiveness. The aim of this work is to develop and validate an MR biomarker of neuroinflammation using MR Spectroscopy (MRS) and chemical exchange saturation transfer imaging (CEST). First, intravenous administration of lipopolysaccharide (LPS) is used as a mild inflammatory stimulus in wild type mice and in a mouse model of Alzheimer’s disease (AD). Elevated levels of the osmolyte myo-inositol, measured with MRS and microglia activation are found in AD mice after LPS administration. Due to the inherent low spatial resolution of MRS, a CEST MRI method is developed next. A myo-inositol CEST protocol is optimised, using Matlab simulations based on the Bloch-McConnell equations for a three pool model, in order to maximize the contrast and to estimate the amount of signal that can be expected in vivo. In vitro and in vivo tests are presented and a fast CEST sequence is developed, while the experimental difficulties and limitations of the technique are discussed. A CEST protocol is finally applied to evaluate the metabolite response to an LPS inflammatory challenge using MRS and histology as validation. A correlation is described between CEST and MRS myo-inositol levels, as well as between CEST and microglia concentration (Iba1 immunostaining), which highlight the potential of CEST as a non-invasive in vivo neuroinflammatory biomarker.
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Omer, Hammad. "Parallel MRI : tools and applications." Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/10524.
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Magnetic Resonance Imaging (MRI) is a non-ionising imaging modality which can provide excellent soft-tissue contrast because of a large number of flexible contrast parameters. One major limitation of MRI is its long acquisition time. Parallel MRI provides a framework to reduce the scan time. The aim of this thesis is to investigate and develop new methods to improve the performance of Parallel MRI. A new GUI (Graphical User Interface) based platform is developed using Matlab which provides an interactive environment to apply different Parallel MRI algorithms as well as helps to analyse the results. Regularization based reconstruction in Parallel MRI utilizes some prior information about the image to achieve better reconstruction results. The use of regularization in Parallel MRI is investigated and a new algorithm is proposed which uses wavelet-denoising of the coil sensitivity estimates before applying SENSE (a Parallel MRI algorithm). The results show that the proposed method is computationally efficient and offers a good alternative to regularization for lower acceleration factors (AF) in Parallel MRI. A good choice of the regularization parameter in regularization based Parallel MRI reconstructions plays a pivotal role to have good results. A new algorithm to choose the regularization parameter efficiently has been developed. This method uses the g-Factor (noise amplification parameter in Parallel MRI) as a regularization parameter and provides better reconstruction results than the contemporary methods. The proposed algorithm improves the computational efficiency of regularization based reconstructions in Parallel MRI. The use of Parallel MRI in interventional imaging can greatly reduce the time required for imaging. A novel catheter based phased array coil, composed of two independent coil elements has been developed. This phased array receiver coil can implement Parallel MRI. Some initial imaging experiments using this coil system have been performed and the results show a successful implementation of Parallel MRI on the acquired data.
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Kudlička, Petr. "Metody akvizice pro DCE-MRI." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2013. http://www.nusl.cz/ntk/nusl-220035.
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In my master’s thesis I describe basics of magnetic resonance measurement. I focus on methods of DCE-MRI with T1 weighting image. I mention some basic contrast agents which are used in MRI imaging. I describe some of pulse sequences which are used in experimental part of my thesis. There I measure contrast in the sample. The measurement is performed in accordance with an acquisition protocol I have proposed. The experiment part was realized on 1.5 T magnet at Masaryk Oncological Institute in Brno. I improved software which is use to research of MR IR TurboFLASH’s data and made software which is use to evaluation perfuse analysis ours measured sequences. At the end I made a discussion about gained facts.
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Dvořáková, Lenka. "Kvantifikace T1 pro preklinické MRI." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2014. http://www.nusl.cz/ntk/nusl-220864.
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T1 mapping of myocardial tissue is important for diagnostics of myocardial fibrosis. Cardiac magnetic resonance imaging of small animals is challenging due to high heart and respiratory rates. Pulse sequences for T1 mapping are proposed in this thesis based on inversion recovery FLASH and Intragate FLASH. The sequence IR FLASH was compared to the reference sequence RARE on a static phantom. Both sequences were applied for measuring the myocardium of a rat. For T1 quantification a software in Matlab was developed. Using this software, T1 maps of rat myocardium were calculated.
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Filipová, Petra. "Dávkové zpracování perfusometrických MRI dat." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2016. http://www.nusl.cz/ntk/nusl-242065.
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This diploma thesis deals with the DCE – MRI method (Dynamic contrast enhanced magnetic resonance imaging). Basic principle of magnetic resonance and pulse sequence is described. The diploma thesis focuses on the DCE method, especially on the description of the processing procedure by this method. Description of selected pharmacokinetic models is the part of this diploma thesis as well. Furthermore, description and realization of batch processing by PerfLab system is presented. For verifying purposes of the batch processing functionality real data were measured using created acquisition protocol, which is also part of the diploma thesis.
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Falahati, Asrami Farshad. "Alzheimer's Disease Classification using K-OPLS and MRI." Thesis, Linköpings universitet, Medicinsk informatik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-78093.
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In this thesis, we have used the kernel based orthogonal projection to latent structures (K-OPLS) method to discriminate between Alzheimer's Disease patients (AD) and healthy control subjects (CTL), and to predict conversion from mild cognitive impairment (MCI) to AD. In this regard three cohorts were used to create two different datasets; a small dataset including 63 subjects based on the Alzheimer’s Research Trust (ART) cohort and a large dataset including 1074 subjects combining the AddNeuroMed (ANM) and the Alzheimer’s Disease Neuroimaging Initiative (ADNI) cohorts. In the ART dataset, 34 regional cortical thickness measures and 21 volumetric measures from MRI in addition to 3 metabolite ratios from MRS, altogether 58 variables obtained for 28 AD and 35 CTL subjects. Three different K-OPLS models were created based on MRI and MRS measures and their combination. Combining the MRI and the MRS measures significantly improved the discriminant power resulting in a sensitivity of 96.4% and a specificity of 97.1%. In the combined dataset (ADNI and AddNeuroMed), the Freesurfer pipeline was utilized to extract 34 regional cortical thickness measures and 23 volumetric measures from MRI scans of 295 AD, 335 CTL and 444 MCI subjects. The classification of AD and CTL subjects using the K-OPLS model resulted in a high sensitivity of 85.8% and a specificity of 91.3%. Subsequently, the K-OPLS model was used to prospectively predict conversion from MCI to AD, according to the one year follow up diagnosis. As a result, 78.3% of the MCI converters were classified as AD-like and 57.5% of the MCI non-converters were classified as control-like. Furthermore, an age correction method was proposed to remove the effect of age as a confounding factor. The age correction method successfully removed the age-related changes of the data. Also, the age correction method slightly improved the performance regarding to classification and prediction. This resulted in that 82.1% of the MCI converters were correctly classified. All analyses were performed using 7-fold cross validation. The K-OPLS method shows strong potential for classification of AD and CTL, and for prediction of MCI conversion.
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Laturra, Mariagrazia. "Imaging multimodale dell’encefalo: confronto fra co-registazione PET e MRI e imaging ibrido PET-MRI." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2018.
Find full textAbstract:
Fra le tecniche per lo studio dell’ imaging metabolico ci sono l’ MRI e la PET: l’ MRI fornisce informazioni strutturali e funzionali attraverso immagini caratterizzate da un’ ottima risoluzione spaziale e dalla possibilità di discriminare i vari tessuti molli: in particolare nelle applicazioni cerebrali consente di discriminare al meglio la sostanza bianca da quella grigia; la PET è una tecnica per lo studio dell' imaging metabolico molto utilizzata nella pratica clinica data la sua alta sensibilità nel rilevamento del tracciante e la sua capacità di quantificazione della sua distribuzione con una risoluzione spaziale che però è inferiore all’ MRI. La combinazione di dati eterogenei acquisiti con le due diverse metodiche permette di ottenere informazioni complementari di aiuto sia per la diagnosi clinica che per lo studio dei meccanismi patologici alla base di molte patologie. La combinazione è possibile utilizzando due approcci: attraverso la co-registrazione dei due tipi di immagini che permette di fondere insieme le informazioni provenienti da uno stesso paziente, acquisite in due sessioni distinte di PET e MR, via software o attraverso l’ uso di scanner ibridi che integrano le due modalità in un unico sistema hardware. Mentre da un punto di vista economico i moderni scanner ibridi risultano più onerosi, d’ altro canto permettono di ottenere performance migliori e di diminuire sia le tempistiche legate al post-processing dei dati acquisiti che la durata della scansione, migliorando il comfort del paziente. In questa tesi sono analizzati i due approcci di combinazione attraverso il confronto fra la procedura di co-registrazione e le acquisizioni di imaging ibrido PET-MR. Le due metodiche sono analizzate sotto il profilo tecnico-fisico e della procedura di post-processing dei dati acquisiti, valutando anche l' aspetto economico, logistico e di comfort del paziente e le prospettive future che potrebbero migliorare entrambi gli approcci.
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Smart, Sean Christopher. "NMR examinations of control and ischemic rodent brain tissue." Thesis, Queen Mary, University of London, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.309450.
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Yan, Jiun-Lin. "Characterising peritumoural progression of glioblastoma using multimodal MRI." Thesis, University of Cambridge, 2017. https://www.repository.cam.ac.uk/handle/1810/267740.
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Glioblastoma is a highly malignant tumor which mostly recurs locally around the resected contrast enhancement. However, it is difficult to identify tumor invasiveness pre-surgically, especially in non-enhancing areas. Thus, the aim of this thesis was to utilize multimodal MR technique to identify and characterize the peritumoral progression zone that eventually leads to tumor progression. Patients with newly diagnosed cerebral glioblastoma were included consecutively from our cohort between 2010 and2014. The presurgical MRI sequences included volumetric T1-weighted with contrast, FLAIR, T2-weighted, diffusion-weighted imaging, diffusion tensor and perfusion MR imaging. Postsurgical and follow-up MRI included structural and ADC images. Image deformation, caused by disease nature and surgical procedure, renders routine coregistration methods inadequate for MRIs comparison between different time points. Therefore, a two-staged non-linear semi-automatic coregistration method was developed from the modification of the linear FLIRT and non-linear FNIRT functions in FMRIB’s Software Library (FSL). Utilising the above mentioned coregistration method, a volumetric study was conducted to analyse the extent of resection based on different MR techniques, including T1 weighted with contrast, FLAIR and DTI measures of isotropy (DTI-p) and anisotropy (DTI-q). The results showed that patients can have a better clinical outcome with a larger resection of the abnormal DTI q areas. Further study of the imaging characteristics of abnormal peritumoural DTI-q areas, using MRS and DCS-MRI, showed a higher Choline/NAA ratio (p = 0.035), especially higher Choline (p = 0.022), in these areas when compared to normal DTI-q areas. This was indicative of tumour activity in the peritumoural abnormal DTI-q areas. The peritumoural progression areas were found to have distinct imaging characteristics. In these progression areas, compared to non-progression areas within a 10 mm border around the contrast enhancing lesion, there was higher signal intensity in FLAIR (p = 0.02), and T1C (p < 0.001), and there were lower intensity in ADC (p = 0.029) and DTI-p (p < 0.001). Further applying radiomics features showed that 35 first order features and 77 second order features were significantly different between progression and non-progression areas. By using supervised convolutional neural network, there was an overall accuracy of 92.4% in the training set (n = 37) and 78.5% in the validation set (n=14). In summary, multimodal MR imaging, particularly diffusion tensor imaging, can demonstrate distinct characteristics in areas of potential progression on preoperative MRI, which can be considered potential targets for treatment. Further application of radiomics and machine learning can be potentially useful when identifying the tumor invasive margin before the surgery.
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Saleh, Muhammad G. "Methods and adaptations required to perform small-animal MRI scanning using a large bore clinical MRI." Master's thesis, University of Cape Town, 2012. http://hdl.handle.net/11427/22098.
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Small-animal imaging has been widely implemented to study succession of disease, therapeutic treatments and the effects of environmental insults. The gold standard noninvasive technique for following progression of heart failure in small-animal models is magnetic resonance imaging (MRI). The aim of this project was to adapt a clinical MRI system to perform small-animal cardiac MRI. The first part of the thesis describes the adaptations required, which included design and construction of a small-animal radiofrequency (RF) coil, physical support (cradle), a core body temperature regulation system, and optimization of pulse sequences. The system was validated using a phantom and in-vivo in 5 healthy rats. The signal-to-noise ratio (SNR) in the phantom was 91% higher using the small-animal coil compared to the standard head coil. SNRs of 7 ± 2 and 18.9 ± 0.6 were achieved in myocardium and blood, respectively, in healthy rats and MR left ventricular mass (LVM) was highly correlated with (r=0.87) with post-mortem mass. In the second part of the study, left ventricular remodeling (LVR) was investigated in a nonreperfused model of myocardial infarction (MI) in 5 sham and 7 infarcted rats. Rats were scanned at 2 and 4 weeks post surgery to allow for global and regional functional and structural analyses of the heart. Images were of sufficient quality to enable semi-automatic segmentation using Segment. Significant increase in end-systolic volume (ESV) was observed in MI rats at 2 weeks post surgery. At 4 weeks post surgery, end-diastolic volume (EDV) and ESV of MI rats were significantly higher than in sham rats. Ejection fraction (EF) of MI rats dropped significantly at 2 weeks and a further significant drop was observed at 4 weeks indicating contractile dysfunction. Wall thickness (WTh) analyses in MI rats at 4 weeks revealed significant reduction in end-diastolic (ED) wall thickness in the anterior region due to necrosis of myocytes. In the posterior region, WTh was significantly higher due to LV hypertrophy. At end-systole (ES), the MI rats revealed significant decrease in WTh in the anterior and lateral regions. MI rats suffered reduction in systolic wall thickening in all regions of the heart, indicating global contractile dysfunction.
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Morell, Arvid. "Perfusion measurements by dynamic susceptibility MRI." Licentiate thesis, Uppsala universitet, Enheten för radiologi, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-143053.
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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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Ridha, Basil Hassan. "MRI in Alzheimer's disease: beyond exclusion." Thesis, Imperial College London, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.486616.
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Brain imaging has been mainly used to exclude other secondary causes of dementia, the past decade has highlighted a wider potential role of magnetic resonance imaging in the diagnosis and monitoring progression of Alzheimer's disease. Using a cohort of subjects with autosomal dominant Alzheimer's disease, I found that atrophy rate of the hippocampus, a medial temporal lobe structure crucially involved in memory processing, to be increased at least 5.5 years prior to the onset of the clinical diagnosis of Alzheimer's disease. Rates of whole brain atrophy lagged behind by 2 years. I compared focal and global measures of atrophy on magnetic resonance imaging with decline in performance on cognitive and functional scales in the context of a realistic multi-centre clinical trial. In mild-tomoderate stages of Alzheimer's disease, measures of global atrophy (rate of whole brain atrophy and ventricular enlargement) were associated more closely ~ith decline in performance on cognitive and functional scales than was rate of hippocampal atrophy. Measures of medial temporal lobe atrophy conventionally rely either on manual volumetric measurement, which is time consuming, or on a visual rating scale, which is not designed to track disease progression. I describe an automated technique - the Automated Temporal Lobe Atrophy Scale, relying on intensity measurement using volumetric Tl-weighted imaging as a measure of medial temporal atrophy. The method is quick, simple, and may have potential to track disease progression. Few studies have demonstrated the value of novel magnetic resonance imaging techniques that reflect the microstructural pathological changes magnetization transfer imaging a'nd diffusion-weighted imaging.. Here, I demonstrate that certain quantitative parameters of such techniques are altered by the disease process over-and-above atrophy measurements. This suggests that such imaging techniques may provide complementary information to conventional volumetric measurement in detecting the Alzheimer's disease process.
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Dyke, Lara Michéle. "Development of a clinical MRI dosimeter." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/mq22592.pdf.
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