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Dissertations / Theses on the topic 'T1-weighted magnetic resonance imaging'

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Published: 10 December 2022
Last updated: 29 January 2023

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1

Williams, Catherine F. M. "Diffusion-weighted magnetic resonance imaging techniques." Thesis, University of Aberdeen, 1998. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU602003.

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The aim of this project was to compare and evaluate other, non-EPI, diffusion-weighted MRI (DWI) sequences, through imaging experiments, on a phantom and in vivo, (using a 0.95 T system) and computer simulations, and to develop improved DWI methodology which could be implemented on standard hardware. Pulsed gradient spin echo (PGSE) and diffusion-weighted STEAM are slow multiple shot sequences, with measurement times of several minutes. Both sequences are highly sensitive to patient motion, but motion artifact was virtually eliminated using navigator echo phase correction and EGG triggering when diffusion-sensitisation was in the phase-encoding direction. It was demonstrated that both sequences can provide high quality images and allow accurate and straightforward diffusion-coefficient measurement when an imaging time period in the region of 20-30 minutes is available and when diffusion-sensitisation is required in one or two directions. A third direction of diffusion-sensitisation may be feasible if more sophisticated immobilisation or phase correction techniques are employed. A choice between PGSE or STEAM for a given application should take account of the Ti and T2 values of the imaged tissues, since a higher SNR might be provided by STEAM when the T1T2 ratio is high. A diffusion-weighted CE-FAST sequence was implemented with the novel modification of acquisition of a navigator gradient-echo, which was shown to reduce motion artifact when diffusion-sensitisation was in the phase-encoding direction. However, it has been demonstrated by other workers that unknown signal losses due to motion-induced phase incoherence between signal components may remain. The SNR (normalised with respect to the square root of the imaging time) in the phantom and in white matter was similar to that obtained using PGSE, but an advantage of CE- FAST is that it can be performed in a fraction of the measurement time of PGSE. Diffusion-sensitivity was much higher than in other sequences and the diffusion- attenuation was found to agree with an analysis presented in the literature. However, a major disadvantage of the technique, which precludes its use for many DWI applications, is the requirement of accurate knowledge of Ti, T2 and flip angle in order to calculate the diffusion coefficient or tensor. Prior to a study of diffusion-weighted snapshot FLASH, the effects of magnetisation evolution during snapshot FLASH acquisition on image quality and parameter measurement accuracy were first investigated, through phantom experiments and computer simulations, in the context of a r2-weighted snapshot FLASH sequence. It was demonstrated that magnetisation evolution effects can lead to significant error in parameter measurement, but that this error can be eliminated by using crusher gradients to prevent evolved magnetisation from contributing to the acquired signal. However, qualitative effects are not entirely eliminated, since a significant degree of edge blurring may remain, and there is a 50% loss of SNR inherent to the crusher gradient technique. It was then shown, theoretically and experimentally, that in diffusion-weighted snapshot FLASH, the crusher gradient technique not only addresses the problem of magnetisation evolution, but also eliminates the effect of phase shifts arising during the diffusion-preparation sequence.
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2

McNab, Jennifer A. "High Resolution Diffusion-Weighted Magnetic Resonance Imaging." Thesis, University of Oxford, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.504436.

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3

Young, Victoria Eleanor Louise. "Enhancement of carotid magnetic resonance imaging with diffusion weighted imaging." Thesis, University of Cambridge, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648278.

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4

Brand, Jonathan F., Lars R. Furenlid, Maria I. Altbach, Jean-Philippe Galons, Achyut Bhattacharyya, Puneet Sharma, Tulshi Bhattacharyya, Ali Bilgin, and Diego R. Martin. "Task-based optimization of flip angle for fibrosis detection in T1-weighted MRI of liver." SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS, 2016. http://hdl.handle.net/10150/622346.

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Chronic liver disease is a worldwide health problem, and hepatic fibrosis (HF) is one of the hallmarks of the disease. The current reference standard for diagnosing HF is biopsy followed by pathologist examination; however, this is limited by sampling error and carries a risk of complications. Pathology diagnosis of HF is based on textural change in the liver as a lobular collagen network that develops within portal triads. The scale of collagen lobules is characteristically in the order of 1 to 5 mm, which approximates the resolution limit of in vivo gadolinium-enhanced magnetic resonance imaging in the delayed phase. We use MRI of formalin-fixed human ex vivo liver samples as phantoms that mimic the textural contrast of in vivo Gd-MRI. We have developed a local texture analysis that is applied to phantom images, and the results are used to train model observers to detect HF. The performance of the observer is assessed with the area-under-the-receiver-operator-characteristic curve (AUROC) as the figure-of-merit. To optimize the MRI pulse sequence, phantoms were scanned with multiple times at a range of flip angles. The flip angle that was associated with the highest AUROC was chosen as optimal for the task of detecting HF. (C) The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.
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5

MA, DAN. "Magnetic Resonance Fingerprinting." Case Western Reserve University School of Graduate Studies / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=case1426170542.

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6

Frost, Stephen Robert. "Diffusion-weighted magnetic resonance imaging with readout-segmented echo-planar imaging." Thesis, University of Oxford, 2012. https://ora.ox.ac.uk/objects/uuid:94421cdc-6bcb-49c2-b9d9-64e016b875f8.

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Diffusion-weighted (DW) magnetic resonance imaging is an important neuroimaging technique that has successful applications in diagnosis of ischemic stroke and methods based on diffusion tensor imaging (DTI). Tensor measures have been used for detecting changes in tissue microstructure and for non-invasively tracing white matter connections in vivo. The most common image acquistion strategy is to use a DW single-shot echo-planar imaging (ss-EPI) pulse sequence, which is attractive due to its robustness to motion artefacts and high imaging speed. However, this sequence has limited achievable spatial resolution and suffers from geometric distortion and blurring artefacts. Readout-segmented echo-planar imaging (rs-EPI) is a DW sequence that is capable of acquiring high-resolution images by segmenting the acquisition of k- space into multiple shots. The fast, short readouts reduce distortion and blurring and the problem of artefacts due to motion-induced phase changes between shots can be overcome with navigator techniques. The rs-EPI sequence has two main shortcomings. (i) The method is slow to produce image volumes, which is limiting for clinical scans due to patient welfare and prevents us from acquiring very many directions in DTI. (ii) The sequence (like other diffusion techniques) is far from the optimum repetition time (TR) for acquiring data with the highest possible signal-to-noise ratio (SNR) in a given time. The work in this thesis seeks to address both of these important issues using a range of approaches. In Chapter 4 a partial Fourier extension is presented, which addresses point (i) by reducing the number of readout segments acquired and estimating the missing data. This allows reductions in scan time by approximately 40% and the reliability of the images is demonstrated in comparisons with the original images. The application of a simultaneous multi-slice scheme to rs-EPI, to address points (i) and (ii), is described in Chapter 5. Using the slice-accelerated rs-EPI sequence, tractography data were compared to ss-EPI data and high-resolution trace-weighted data were acquired in clinically relevant scan times. Finally, a 3D multi-slab extension that addresses point (i) is presented in Chapter 6. A 3D sequence could also allow higher resolution in the slice direction than 2D multi-slice methods, which are limited by the difficulties in exciting thin, accurate slices. A 3D version of rs-EPI was simulated and implemented and a k-space acquisition synchronised to the cardiac cycle showed substantial improvements in image artefacts compared to a conventional k-space acquisition.
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7

Higgins, David Michael. "T1 measurement for quantitative myocardial perfusion assessment with magnetic resonance imaging." Thesis, University of Leeds, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.421378.

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8

Cameron, Donnie. "Quantitative T1 magnetic resonance imaging in the myocardium : development and clinical applications." Thesis, University of Aberdeen, 2013. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=202753.

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Background: Qualitative magnetic resonance imaging methods, such as T2-weighted (T2W) imaging, are commonly used for cardiac tissue characterisation. However, these are sensitive to image artefact, and results are unreliable. Modified Look-Locker inversion recovery (MOLLI) provides robust, quantitative T1 imaging in the myocardium, but it is subject to limitations: its T1 measurement accuracy is dependent on heart rate, it exhibits banding artefacts, and a lengthy breath hold is required. In this thesis, some MOLLI variants were developed with the aim of mitigating these problems. Furthermore, MOLLI was applied to two different patient groups for comparison with a typical T2W method. Methods: MOLLI variants used alternative k-space trajectories, gradient-echo readouts, startup preparations, and sampling schemes, and were tested in silico, in vitro and in vivo—in healthy volunteers. In patients, conventional MOLLI was compared to T2W spectral attenuated inversion recovery (SPAIR) for oedema detection in both acute ST-segment elevation myocardial infarction (STEMI), and Takotsubo cardiomyopathy (TCM). RESULTS: Simulation, phantom and volunteer data showed that a linear sweep up (skipped pulse pair) startup preparation enables improved T1 measurements. A MOLLI variant with a reduced sampling scheme performed similarly to conventional MOLLI, allowing for shorter breath holds. Different k-space trajectories did not significantly affect T1 measurement accuracy, but precision varied: possibly due to artefacts. For oedema identification, MOLLI performed significantly better than T2W-SPAIR in STEMI patients, and the two were comparable in TCM patients. In all patients, remote myocardium showed an elevated T1 relative to healthy volunteers, suggesting remote inflammation. Conclusions: It was shown that MOLLI T1 mapping can delineate oedema in acute STEMI and TCM patients, producing measurements that are more robust and reproducible than those made with T2W SPAIR. A number of improvements were suggested in this work, but there is still substantial scope for developing the MOLLI T1 mapping pulse sequence.
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9

Guinn, Amy Rebecca. "A New Magnetic Resonance Imaging Contrast Agent for the Detection of Glutathione." Thesis, Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/10432.

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Magnetic resonance imaging (MRI) is one of the most powerful imaging techniques for research and clinical diagnosis. To expand upon the intrinsic capabilities of MRI, new contrast agents that can detect the presence of biomarkers in vivo are being developed. My Masters thesis research focuses on the design and synthesis of a new MRI contrast agent that can detect glutathione (GSH), a biomarker that has been implicated in a number of oxidative stress diseases. This new MRI contrast agent is based on chelated dysprosium (Dy), an inorganic metal, which provides negative contrast to surrounding tissue. Preliminary data has shown that attaching a poly(ethylene glycol) (PEG) chain to the Dy chelate, effectively increasing its molecular weight, enhances the contrast ability of Dy. Using this new information, the contrast agent was designed to have a large molecular weight PEG chain attached to the Dy chelate through a disulfide, creating a thiol-sensitive linkage. In the presence of a thiol-containing molecule such as GSH, the Dy will be dePEGylated through a disulfide exchange reaction, removing the molecular weight effect of the PEG, and allowing for the detection of GSH by MRI. This new MRI contrast agent could provide insight into the progression and diagnosis of oxidative stress pathologies associated with GSH.
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10

McGraw, Tim E. "Denoising, segmentation and visualization of diffusion weighted MRI." [Gainesville, Fla.] : University of Florida, 2005. http://purl.fcla.edu/fcla/etd/UFE0011618.

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11

Biffar, Andreas. "Quantitative Analysis of Diffusion-weighted Magnetic Resonance Imaging in the Spine." Diss., lmu, 2010. http://nbn-resolving.de/urn:nbn:de:bvb:19-126230.

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12

Shokouhimehr, Mohammadreza. "Prussian Blue Nanoparticles and its Analogues as New-Generation T1-Weighted MRI Contrast Agents for Cellular Imaging." Kent State University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=kent1275612500.

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13

Shimizu, Hironori. "Comparison of acquired diffusion weighted imaging and computed diffusion weighted imaging for detection of hepatic metastases." Kyoto University, 2015. http://hdl.handle.net/2433/200435.

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14

Metwalli, Nader. "High angular resolution diffusion-weighted magnetic resonance imaging: adaptive smoothing and applications." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/34854.

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Diffusion-weighted magnetic resonance imaging (MRI) has allowed unprecedented non-invasive mapping of brain neural connectivity in vivo by means of fiber tractography applications. Fiber tractography has emerged as a useful tool for mapping brain white matter connectivity prior to surgery or in an intraoperative setting. The advent of high angular resolution diffusion-weighted imaging (HARDI) techniques in MRI for fiber tractography has allowed mapping of fiber tracts in areas of complex white matter fiber crossings. Raw HARDI images, as a result of elevated diffusion-weighting, suffer from depressed signal-to-noise ratio (SNR) levels. The accuracy of fiber tractography is dependent on the performance of the various methods extracting dominant fiber orientations from the HARDI-measured noisy diffusivity profiles. These methods will be sensitive to and directly affected by the noise. In the first part of the thesis this issue is addressed by applying an objective and adaptive smoothing to the noisy HARDI data via generalized cross-validation (GCV) by means of the smoothing splines on the sphere method for estimating the smooth diffusivity profiles in three dimensional diffusion space. Subsequently, fiber orientation distribution functions (ODFs) that reveal dominant fiber orientations in fiber crossings are then reconstructed from the smoothed diffusivity profiles using the Funk-Radon transform. Previous ODF smoothing techniques have been subjective and non-adaptive to data SNR. The GCV-smoothed ODFs from our method are accurate and are smoothed without external intervention facilitating more precise fiber tractography. Diffusion-weighted MRI studies in amyotrophic lateral sclerosis (ALS) have revealed significant changes in diffusion parameters in ALS patient brains. With the need for early detection of possibly discrete upper motor neuron (UMN) degeneration signs in patients with early ALS, a HARDI study is applied in order to investigate diffusion-sensitive changes reflected in the diffusion tensor imaging (DTI) measures axial and radial diffusivity as well as the more commonly used measures fractional anisotropy (FA) and mean diffusivity (MD). The hypothesis is that there would be added utility in considering axial and radial diffusivities which directly reflect changes in the diffusion tensors in addition to FA and MD to aid in revealing neurodegenerative changes in ALS. In addition, applying adaptive smoothing via GCV to the HARDI data further facilitates the application of fiber tractography by automatically eliminating spurious noisy peaks in reconstructed ODFs that would mislead fiber tracking.
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15

Lawrence, Edward Malnor. "Quantitative diffusion-weighted magnetic resonance imaging for the assessment of prostate cancer." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.709007.

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16

Khayal, Inas Samir. "Characterization of diffusion weighted magnetic resonance imaging for patients with brain tumors." Diss., Search in ProQuest Dissertations & Theses. UC Only, 2009. 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:3378496.

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Thesis (Ph.D.)--University of California, San Francisco with the University of California, Berkeley, 2009.
Source: Dissertation Abstracts International, Volume: 70-10, Section: B, page: 6381. Adviser: Sarah J. Nelson.
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17

Cook, Philip Anthony. "Modelling uncertainty in brain fibre orientation from diffusion-weighted magnetic resonance imaging." Thesis, University College London (University of London), 2006. http://discovery.ucl.ac.uk/1445463/.

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Diffusion-weighted magnetic resonance imaging (DW-MRI) permits in-vivo measurements of water diffusion, from which we can infer the orientation of white matter fibres in the brain. We show that by ordering the measurements, we can improve the reproducibility of the fibre-orientation estimate from partially-completed DW-MRI scans, without altering the complete data set. Tractography methods reconstruct entire fibre pathways from the local fibre-orientation estimates. Because the local fibre-orientation measurements are subject to uncertainty, the reconstructed fibre pathways are best described with a probabilistic algorithm. One way to estimate the connection probabilities is by defining a probability density function (PDF) in each voxel, and sampling from the PDF in a Monte-Carlo fashion. We propose new models of the PDF based on standard spherical statistical methods. The models improve previous work by closely modelling the dispersion of repeated noisy estimates of the fibre orientation. We compare a simple PDF (the Watson PDF) that models circular cluster of axes to a more general PDF (the Bingham PDF) that models circular or elliptical clusters of axes. We also propose models of the PDF in regions of crossing fibres, where there are two distinct fibre populations in the voxel. We validate the PDFs by comparing them to the uncertainty in fibre orientation calculated from bootstrap resampling of a repeated brain MR acquisition. We find mat the Bingham PDF produces connection probabilities that are closer to the bootstrap results man the Watson PDF. We use the new PDF models to perform a connectivity-based segmentation of the corpus callosum in eight different subjects. The results are similar to those of previous studies on corpus callosum connectivity, despite the use of finer cortical labelling, suggesting that the dominant connections from the corpus callosum project to the superior frontal gyrus, the superior parietal gyrus and the occipital gyrus.
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18

Jones, Catherine Elizabeth. "Studies of the crystalline lens using magnetic resonance imaging." Thesis, Queensland University of Technology, 2004. https://eprints.qut.edu.au/15950/1/Catherine_Jones_Thesis.pdf.

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The eye lens grows continuously throughout life and changes its shape as the eye changes focus from a distant to a near object (the process of accommodation). These changes are complex because they may affect not only the shape of the lens, but also its refractive index distribution. To date there has been no satisfactory technique for directly and non-invasively measuring these changes. In this study the refractive index distribution through the isolated lens was measured non-invasively using a novel MRI technique. The dependence of the refractive index value of lens tissue on its transverse relaxation rate (R2) was determined empirically from measurements on lens homogenate samples. Using a multi-spin-echo imaging sequence, data were acquired for constructing R2 maps of a central slice through the isolated lens. These R2 maps were transformed to refractive index maps using the empirically determined dependence of refractive index on R2. Using a standard algorithm for ray tracing through gradient index media, the propagation of light rays through the index map were simulated. The optical properties of the lens, such as focal length, were then measured. The technique was validated by also directly measuring the focal length of each lens using laser ray tracing. The subtle changes in refractive index distribution that are responsible for the dramatic change in the optical properties of the isolated lens with age, were observed for the first time. The decrease in surface power of the isolated lens with age accounted only partially for the decrease in total lens power with age, the remainder resulting from a reduction in the gradient of refractive index (GRIN) power. It is likely that this reduction in GFUN power is the mechanism by which the eye maintains emmetropia (good distant vision) with age despite the increasing curvature of its surfaces. The reduction in the GRIN power of the lens was found to be mainly due to a flattening of the refractive index profile in the central region of the lens, accompanied by steepening of the profile near the edge of the lens. In agreement with a previous MRI study of the isolated human eye lens, this study found a decrease in the refractive index of the nucleus with age. However the age related change in this study was not as large and not found to be statistically significant. The results demonstrate that existing simple models for the optics of the eye lens are inadequate to accurately describe its properties. Several more sophisticated models were considered in an attempt to describe better the age-dependent changes that occur in both the power of the lens and its longitudinal aberration. Mathematical modelling was also used to simulate the accommodative process and investigate possible changes in the index distribution of the lens that may occur with accommodation. A preliminary in vivo study was performed aimed at observing the change in the refractive index distribution of the eye lens with age and accommodation. These results demonstrated the feasibility of the technique for in vivo applications and showed that within experimental error there is little change in the central refractive index of the lens with age. However the resolution achievable with standard clinical imaging sequences and signal detection hardware was not optimal for in vivo refractive index mapping of changes in the human eye lens with accommodation. Finally therefore, methods for refining the technique for in vivo applications are discussed which may make it possible to directly and simultaneously measure both the shape and refractive index distribution of the lens with age and accommodation.
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19

Jones, Catherine Elizabeth. "Studies of the crystalline lens using magnetic resonance imaging." Queensland University of Technology, 2004. http://eprints.qut.edu.au/15950/.

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The eye lens grows continuously throughout life and changes its shape as the eye changes focus from a distant to a near object (the process of accommodation). These changes are complex because they may affect not only the shape of the lens, but also its refractive index distribution. To date there has been no satisfactory technique for directly and non-invasively measuring these changes. In this study the refractive index distribution through the isolated lens was measured non-invasively using a novel MRI technique. The dependence of the refractive index value of lens tissue on its transverse relaxation rate (R2) was determined empirically from measurements on lens homogenate samples. Using a multi-spin-echo imaging sequence, data were acquired for constructing R2 maps of a central slice through the isolated lens. These R2 maps were transformed to refractive index maps using the empirically determined dependence of refractive index on R2. Using a standard algorithm for ray tracing through gradient index media, the propagation of light rays through the index map were simulated. The optical properties of the lens, such as focal length, were then measured. The technique was validated by also directly measuring the focal length of each lens using laser ray tracing. The subtle changes in refractive index distribution that are responsible for the dramatic change in the optical properties of the isolated lens with age, were observed for the first time. The decrease in surface power of the isolated lens with age accounted only partially for the decrease in total lens power with age, the remainder resulting from a reduction in the gradient of refractive index (GRIN) power. It is likely that this reduction in GFUN power is the mechanism by which the eye maintains emmetropia (good distant vision) with age despite the increasing curvature of its surfaces. The reduction in the GRIN power of the lens was found to be mainly due to a flattening of the refractive index profile in the central region of the lens, accompanied by steepening of the profile near the edge of the lens. In agreement with a previous MRI study of the isolated human eye lens, this study found a decrease in the refractive index of the nucleus with age. However the age related change in this study was not as large and not found to be statistically significant. The results demonstrate that existing simple models for the optics of the eye lens are inadequate to accurately describe its properties. Several more sophisticated models were considered in an attempt to describe better the age-dependent changes that occur in both the power of the lens and its longitudinal aberration. Mathematical modelling was also used to simulate the accommodative process and investigate possible changes in the index distribution of the lens that may occur with accommodation. A preliminary in vivo study was performed aimed at observing the change in the refractive index distribution of the eye lens with age and accommodation. These results demonstrated the feasibility of the technique for in vivo applications and showed that within experimental error there is little change in the central refractive index of the lens with age. However the resolution achievable with standard clinical imaging sequences and signal detection hardware was not optimal for in vivo refractive index mapping of changes in the human eye lens with accommodation. Finally therefore, methods for refining the technique for in vivo applications are discussed which may make it possible to directly and simultaneously measure both the shape and refractive index distribution of the lens with age and accommodation.
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20

McDowell, Amy Rebecca. "Imaging T1, T2 and myelin water fraction in the post-mortem multiple sclerosis central nervous system." Thesis, Queen Mary, University of London, 2017. http://qmro.qmul.ac.uk/xmlui/handle/123456789/24711.

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The subject of this thesis is the use of Magnetic Resonance (MR) Imaging to quantify biometric MR indices in the Multiple Sclerosis (MS) fixed post-mortem central nervous system (CNS) tissue. Evaluating these indices in fixed tissue allows for the use of histology to verify the findings of MRI. However, it must first be discovered if the indices can be evaluated in fixed post-mortem spinal cord tissue. There is very little literature in this specific area, though some in the fixed brain, the results of which have been assumed to be equivalent in the spinal cord without proof. Therefore, the methodology must first be verified before the consideration of any index as useful and translatable to in-vivo spinal cord. This thesis concentrates on the evaluation of MR relaxometry methods using the indices T1 and T2 by themselves and to evaluate the myelin content of fixed post-mortem CNS tissue. The Carr-Purcell-Meiboom-Gill (CPMG) and Multicomponent Driven Equilibrium Single Pulse Observation of T1 & T2 (mcDESPOT) sequences are used to calculate T1, T2 and the Myelin Water Fraction (MWF) which is believed to be proportional to myelin content in the CNS. This is performed at 3T in a clinical scanner and at 7T in a small animal and wholebody scanner. The methods are first evaluated for use in fixed post-mortem CNS tissue. The two myelin measurement methods are then compared to histological staining if appropriate and where available to verify that the results obtained are proportional to myelin content. The T1 and T2 values in fixed tissue were found to be shortened in fixed tissue, T2 values were so short as to be at the limits of measurement by a clinical scanner, and values converged in white and grey matter, and therefore contrast was found to be limited between these tissues. Proton density images provided the most contrast between tissues. However, even with shortened T2 values, the CPMG sequence was able to identify the myelin water component in fixed tissue. The mcDESPOT algorithm struggled to separate the myelin water component due to clinical scanner limitations and the shortened, converging T1 and T2 values. However, the mcDESPOT algorithm was successful in discerning the myelin water component in the high signal situation of a small bore 7T peclinical scanner. An evaluation was then made of the usefulness of these indices for translation into clinical imaging. The CPMG sequence was found to be proportional to myelin content under all conditions, and therefore useful for disease monitoring in demyelinating diseases. The mcDESPOT sequence, was found to be proportional to myelin in some conditions, and is likely to be useful for monitoring myelination, though the sequence could not be fully validated in this thesis.
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21

Howells, Ruairidh. "T₂-weighted BOLD in human myocardium." Thesis, University of Oxford, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.589620.

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The principal aim of this work is to test the viability of Blood Oxygenation Level Dependent (BOLD) measurements in human myocardium, an experiment which has seen promising attempts in recent literature. A central challenge to the ~uccess of these experiments has been in the limited scale of the measured effect; this work therefore includes efforts to separate the BOLD effect from noise and confounding signals. BOLD is then measured by intensity in MR images produced using Steady State Free Precession (SSFP) acquisition, weighted by a T2 preparation module to introduce the target contrast. Two modelling sections are included: first, the changes in physiology which influence the signal intensity in the MR images via the T2 dependence; and secondly the factors upon which the preparation depends, which are not entirely limited to the T2 of the tissue. These models are investigated with the aim of increasing the BOLD contrast and removing any other dependencies. An empirical model is shown to be suitable for the relationship between oxygenation and T2, and improvements are suggested and explained by thorough simulation ofthe preparation module. Compensation for a further confounding effect is also investigated: that of the increase in heart rate which accompanies the adenosine infusion used in the BOLD experiment protocol to reveal differences in the response of ischaemic and healthy tissue. The compensation is shown to reduce temporal variance in SI measurements, and to increase the separation between distributions of SI in tissue classes. A process of registration and segmentation is refined for sampling BOLD information from the SS FP images, and tested to show a low failure rate. Finally, the BOLD process is then tested in a set of human subjects including healthy volunteers and patients with coronary artery disease, investigating the consequent difference in tissue oxygenation. A significant difference is shown in the responses to stress of BOLD SI three tissue classes in these subjects.
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22

Teh, Irvin Tze Wei. "Development of methodologies for diffusion-weighted magnetic resonance imaging at high field strength." Thesis, Imperial College London, 2009. http://hdl.handle.net/10044/1/4715.

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Diffusion-weighted imaging of small animals at high field strengths is a challenging prospect due to its extreme sensitivity to motion. Periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER) was introduced at 9.4T as an imaging method that is robust to motion and distortion. Proton density (PD)-weighted and T2-weighted PROPELLER data were generally superior to that acquired with single-shot, Cartesian and echo planar imaging-based methods in terms of signal-to-noise ratio (SNR), contrast-to-noise ratio and resistance to artifacts. Simulations and experiments revealed that PROPELLER image quality was dependent on the field strength and echo times specified. In particular, PD-weighted imaging at high field led to artifacts that reduced image contrast. In PROPELLER, data are acquired in progressively rotated blades in k-space and combined on a Cartesian grid. PROPELLER with echo truncation at low spatial frequencies (PETALS) was conceived as a post-processing method that improved contrast by reducing the overlap of k-space data from different blades with different echo times. Where the addition of diffusion weighting gradients typically leads to catastrophic motion artifacts in multi-shot sequences, diffusion-weighted PROPELLER enabled the acquisition of high quality, motion-robust data. Applications in the healthy mouse brain and abdomen at 9.4T and in stroke patients at 3T are presented. PROPELLER increases the minimum scan time by approximately 50%. Consequently, methods were explored to reduce the acquisition time. Two k-space undersampling regimes were investigated by examining image fidelity as a function of degree of undersampling. Undersampling by acquiring fewer k-space blades was shown to be more robust to motion and artifacts than undersampling by expanding the distance between successive phase encoding steps. To improve the consistency of undersampled data, the non-uniform fast Fourier transform was employed. It was found that acceleration factors of up to two could be used with minimal visual impact on image fidelity. To reduce the number of scans required for isotropic diffusion weighting, the use of rotating diffusion gradients was investigated, exploiting the rotational symmetry of the PROPELLER acquisition. Fixing the diffusion weighting direction to the individual rotating blades yielded geometry and anisotropy-dependent diffusion measurements. However, alternating the orientations of diffusion weighting with successive blades led to more accurate measurements of the apparent diffusion coefficient while halving the overall acquisition time. Optimized strategies are proposed for the use of PROPELLER in rapid high resolution imaging at high field strength.
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23

Jiang, Yun. "DEVELOPMENT OF NOVEL PULSE SEQUENCES FOR MAGNETIC RESONANCE FINGERPRINTING." Case Western Reserve University School of Graduate Studies / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=case1480691677961147.

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Umapathy, Lavanya, and Lavanya Umapathy. "Assessment of White Matter Integrity in Bonnet Macaque Monkeys using Diffusion-weighted Magnetic Resonance Imaging." Thesis, The University of Arizona, 2016. http://hdl.handle.net/10150/622837.

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Diffusion-weighted magnetic resonance imaging (dMRI) has been used to non-invasively investigate the integrity of white matter and the connectivity of the brain. In this work, high angular resolution diffusion imaging (HARDI), an advanced dMRI methodology was developed and employed in bonnet macaque monkeys to study the connectivity of the orbitofrontal cortex (OFC) and amygdala, two gray matter regions involved in making reward-guided decisions. With age, it is believed that there is a decline in the white matter connectivity between these two regions, also known as uncinate fasciculus (UF), and that this affects reward-value assignment and feedback learning in older adults. The analysis pipeline involved correction for distortions due to eddy currents and field inhomogeneity, noise reduction using a local principal component analysis based technique and subsequent registration to the high-resolution T1-weighted images. Gray matter regions corresponding to OFC and amygdala were identified on the T1-weighted images and probabilistic tractography was carried out to delineate the tracts belonging to UF. The output connectivity map from tractography was used to extract imaging parameters of interest such as fractional anisotropy, axial and radial diffusivity along the UF. A significant reduction in the fractional anisotropy index and the axial diffusivity index along the UF tract was observed with increased age of monkeys. Compared to the left hemisphere, stronger trends were observed in the right hemisphere of the monkeys, indicating possible laterality.
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Kerttula, L. (Liisa). "Magnetic resonance imaging of the intervertebral disc:post-traumatic findings and the value of diffusion-weighted MR imaging." Doctoral thesis, University of Oulu, 2001. http://urn.fi/urn:isbn:9514264711.

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Abstract Magnetic resonance imaging (MRI) provides important information about structural and biochemical changes in organs. MRI is also an effective imaging method for the evaluation of spinal disorders. However, many of its potential applications - particularly diffusion imaging - have not yet been thoroughly explored. The purpose of this study was to determine the MRI-detectable changes in the intervertebral disc after trauma and to test the feasibility of diffusion-weighted MR imaging of the intervertebral discs. A minipig model was used in the experimental study to determine the MRI changes in the intervertebral disc after peripheral annular lesions in different time frames. Three of eight discs with experimental annular lesions had a normal annular appearance in MRI. Annular lesions, when detectable, were manifested as a bulging of the disc or as a high-intensity zone (HIZ) inside the annulus. Either the signal intensity or the area of bright signal intensity in the nucleus had nearly always decreased after one month, but they were still detectable even in cases where no signs of annular trauma could be seen in the MR images. The histology of HIZ is presented for the first time: clusters of nuclear cells and disorganized granulation tissue with capillaries were detected in the HIZ area. Fourteen patients 8 to 21 years of age with histories of vertebral fracture at least one year previously and 14 asymptomatic healthy control subjects 8 to 22 years of age were studied by MRI. In these young people a vertebral fracture, especially with end-plate injury, proved to be a notable risk factor for initiating disc degeneration. The apparent diffusion coefficients (ADCs) of the thoracolumbar intervertebral discs were determined in three orthogonal directions in 18 healthy young volunteers aged 8-22 years. The ADCs were also determined in 10 young patients with previous vertebral fractures, and clear decreases were found in the ADCx and ADCy directions, but in the ADCz direction values had not changed significantly as compared to the values in the controls. The most marked changes were observed in the degenerated discs, followed by those in the discs with a normal signal intensity adjacent to the primary trauma area. Diffusion-weighted MR imaging affords a useful tool for evaluating disc diseases in the early phases. Additionally, 37 adult volunteers without back symptoms were studied by MRI and by magnetic resonance angiography (MRA) and it was found that the status of the lumbar arteries significantly explained the diffusion values in the lumbar intervertebral discs. The correlation between disc degeneration and diffusion was mostly linear, but not significant.
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Waghorn, Benjamin J. "Monitoring dynamic calcium homeostasis alterations by T₁-weighted and T₁-mapping cardiac manganese enhanced MRI (MEMRI) in a murine myocardial infarction model." Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/28237.

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Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2009.
Committee Chair: Hu, Tom; Committee Co-Chair: Rahnema, Farzad; Committee Member: Wang, Chris; Committee Member: Yanasak, Nathan.
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Yoshimura, Hajime. "Status epilepticus in the elderly: Prognostic implications of rhythmic and periodic patterns in electroencephalography and hyperintensities on diffusion-weighted imaging." Kyoto University, 2017. http://hdl.handle.net/2433/227548.

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Bajammal, Mohammad Salem. "Acquisition- and modeling-independent resolution enhancement of brain diffusion-weighted magnetic resonance imaging volumes." Thesis, University of British Columbia, 2016. http://hdl.handle.net/2429/58945.

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Diffusion-weighted magnetic resonance imaging (dwMRI) provides unique capabilities for non-invasive imaging of neural fiber pathways in the brain. dwMRI is an increasingly popular imaging method and has promising diagnostic and surgical applications for Alzheimer's disease, brain tumors, and epilepsy, to name a few. However, one limitation of dwMRI (specifically, the more common diffusion tensor imaging scheme, DTI) is that it suffers from a relatively low resolution. This often leads to ambiguity in determining location and orientation of neural fibers, and therefore reduces the reliability of information gained from dwMRI. Several approaches have been suggested to address this issue. One approach is to have a finer sampling grid, as in diffusion spectrum imaging (DSI) and high-angular resolution imaging (HARDI). While this did result in a resolution improvement, it has the side effects of lowering the quality of image signal-to-noise ratio (SNR) or prolonging imaging time, which hinders its use in routine clinical practice. Subsequently, an alternative approach has been proposed based on super-resolution methods, where multiple low resolution images are fused into a higher resolution one. While this managed to improve resolution without reducing SNR, the multiple acquisitions required still resulted in a prolonged imaging time. In this thesis, we propose a processing pipeline that uses a super resolution approach based on dictionary learning for alleviating the dwMRI low resolution problem. Unlike the majority of existing dwMRI resolution enhancement approaches, our proposed framework does not require modifying the dwMRI acquisition. This makes it applicable to legacy data. Moreover, this approach does not require using a specific diffusion model. Motivated by how functional connectivity (FC) reflects the underlying structural connectivity (SC), we use the Human Connectome Project and Kirby multimodal dataset to quantitatively validate our results by investigating the consistency between SC and FC before and after super-resolving the data. Based on this scheme, we show that our method outperforms interpolation and the only existing single image super-resolution method for dMRI that is not dependent on a specific diffusion model. Qualitatively, we illustrate the improved resolution in diffusion images and illustrate the revealed details beyond what is achievable with the original data.
Applied Science, Faculty of
Graduate
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Lockwood, Estrin Georgia. "Diffusion weighted magnetic resonance imaging of in utero and ex utero human brain development." Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/24997.

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The primary objective of this thesis was to establish quantitative measurements of normal fetal brain tissue across gestation using diffusion magnetic resonance imaging (MRI); the secondary aim was to compare diffusion metrics in fetuses with normal brain development to those with isolated ventriculomegaly (VM), congenital heart disease and in infants born preterm. Fetal diffusion weighted imaging (DWI) was optimised, and a motion-corrected diffusion tensor imaging (DTI) technique was utilized to produce apparent diffusion coefficient (ADC) and fractional anisotropy (FA) values across gestation in normal fetal cohorts. Tract-based spatial statistics (TBSS) was utilised to analyse DTI in neonates with isolated VM compared to controls. Diffusion and volumetric MR data in preterm infants were analysed using an objective segmentation approach to characterise ex utero neurodevelopment, and to establish the effects of perinatal clinical factors on brain development. Normative ADC values were established in the fetal brain (n=52) across a large gestational age range. Increased ADC values were found in fetuses (n=24) and neonates (n=22) with isolated VM compared to controls; decreased FA was also demonstrated in neonates with VM. In preterm neonates (n=208), white and deep grey matter exhibited significantly increasing FA, and decreasing ADC, axial and radial diffusivity measures with increasing age at scan. DTI measures in the cortex significantly decreased with increasing age at scan; volume measures increased in all brain regions. Clinical factors including respiratory support and age at birth affected regional DTI and volumetric measures in preterm infants. FA values from a normal fetal cohort using motion-corrected DTI (n=26) were compared to preterm neonates (n=32) and significant differences were found. This thesis produced normal fetal diffusion data comparable to that produced in neonates. Quantifiable MR techniques can be used to explore the relationship between in utero and ex utero brain development and study alterations of normal fetal maturation.
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Nagahara, Shizue. "Studies on Functional Magnetic Resonance Imaging with Higher Spatial and Temporal Resolutions." 京都大学 (Kyoto University), 2014. http://hdl.handle.net/2433/188540.

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Boyer, Peter Gerard. "A Study of Bioluminescent and Magnetic Resonance Imaging in Murine Glioblastoma Models." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1408624457.

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McHugh, Damien Joseph. "The effect of tumour microstructure on diffusion-weighted MRI measurements." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/the-effect-of-tumour-microstructure-on-diffusionweighted-mri-measurements(9821717e-df69-4dd0-baf7-51cf27a18aa2).html.

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By sensitising the magnetic resonance signal to the diffusion of water molecules in tissue, diffusion-weighted magnetic resonance imaging provides a means of assessing tumour microstructure non-invasively. Such measurements have the potential to provide important information about tumour development and the response of tumours to treatment, but the way in which different tissue properties affect the diffusion-weighted signal remains unclear. Through simulations, in vivo studies and phantom experiments, this thesis investigates the relationship between the diffusion-weighted signal, the pulse sequence parameters used for acquisition, and microstructural properties of tumours. The use of oscillating gradient pulse sequences on a clinical scanner was investigated initially, with theoretical and practical considerations leading subsequent work to focus on pulsed gradient sequences. The forward problem of predicting the diffusion-weighted signal for given combinations of tissue properties and sequence parameters was addressed numerically through Monte Carlo simulations, focussing on how tumour cell size, intracellular volume fraction and membrane permeability affect the signal. These simulations allowed the sensitivity of the signal to changes in these tissue properties to be investigated, revealing how sensitivity depends on sequence parameters as well as the specific microstructural configuration. By repeating the simulations using the specific sequence parameters used in a clinical and preclinical study, the sensitivity of the implemented protocols was assessed, and linked to the experimental findings. The preclinical study illustrated the importance of the diffusion time in determining the sensitivity to treatment-induced changes in tumours, with larger post-treatment signal changes observed at longer diffusion times. These trends were qualitatively reflected in the sensitivity analysis derived from the simulations. Finally, the inverse problem of estimating microstructural properties from the diffusion-weighted signal was addressed using a physical phantom designed as a simple mimic of tumour tissue. By fitting a biophysical model to the diffusion data, the size and volume fraction of the approximately spherical 'cells' were estimated. The radius was slightly underestimated compared with that determined from independent measurements, the fitted volume fraction was plausible, and parameters were found to be estimated with reasonably good precision.
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Niinimäki, J. (Jaakko). "Diffusion-weighted MRI and delayed contrast enhancement of degenerated intervertebral disc." Doctoral thesis, University of Oulu, 2009. http://urn.fi/urn:isbn:9789514291715.

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Abstract Magnetic resonance imaging (MRI) provides methods to study the microstructure and functional properties of tissues that can be utilized to acquire information about the degenerative processes in the spine. The purpose of the current study was to evaluate the value of diffusion-weighted MRI and quantification of delayed gadolinium enhancement in assessing intervertebral disc degeneration. An experimental degeneration model was used to evaluate the sensitivity of diffusion-weighted MRI and T2 relaxation time measurements in detecting early degenerative changes in the disc. In six pigs, an annular disc lesion was induced surgically, after which the discs were repeatedly MR imaged for up to eight weeks. T2 relaxation time of the lesioned discs decreased postoperatively, whereas apparent diffusion coefficient (ADC) initially increased, but at eight weeks decreased when compared to the control discs. The value of ADC in degeneration of human discs was evaluated by imaging 228 voluntary middle-aged men. ADC values of the three lowest lumbar intervertebral discs were measured and disc degeneration was visually graded. The reduction in ADC between visually normal and moderately degenerated discs was 4%, whereas severely degenerated discs showed 5% higher ADC values than normal discs. T2 signal intensity of the discs was significantly correlated with the ADC values. Because of a considerable overlap between ADC values of normal and degenerated discs the clinical relevance of the ADC measurements of lumbar intervertebral discs remains questionable. A method to quantify delayed enhancement of the nucleus pulposus after intravenous gadolinium contrast agent injection was developed to evaluate the diffusion of small solutes into the disc. Twenty male volunteers were imaged in order to correlate the measured change in the T1 relaxation rate with visually evaluated degenerative changes. The percentual change of T1 relaxation rate for individual discs was up to 126%, and a positive trend was observed between the delayed enhancement and the disc degeneration grades. In order to study the factors that determine the intensity of delayed enhancement, T1 relaxation rate measurements were further correlated with lumbar artery stenosis, bone marrow changes adjacent to endplates, endplate defects, and ADC of the disc. Lumbar artery stenosis and ADC values of the discs were not correlated with enhancement, while disc space narrowing and the presence of degenerative endplate changes had a strong correlation, suggesting an important role for the endplate in maintaining the integrity of the disc.
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Røe, Kathrine. "In vivo Magnetic Resonance Spectroscopy and Diffusion Weighted Magnetic Resonance Imaging for Non-Invasive Monitoring of Treatment Response of Subcutaneous HT29 Xenografts in Mice." Thesis, Norwegian University of Science and Technology, Department of Electronics and Telecommunications, 2006. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-9441.

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This work investigates whether in vivo magnetic resonance spectroscopy (MRS) and diffusion-weighted magnetic resonance imaging (DW-MRI) can be used for non-invasive monitoring of treatment response in an experimental tumor model. Twenty-nine nude mice with colorectal adenocarcinoma HT29 xenografts on each flank were included into 2 separate experiments. In the first experiment control tumors were compared to tumors irradiated with 15 Gy at Day 2. MR baseline values were established at Day 1 followed by 4 post-treatment MR examinations. Mice were sacrificed for histological response evaluation and high-resolution ex vivo magic angle spinning (HR-MAS) MRS of tumor tissue samples for correlation with in vivo MR data. The second experiment included 3 groups recieving combined chemoradiation therapy; Control group, Capecitabine (359 mg/kg daily Day 1 - Day 5) group and Capecitabine (359 mg/kg daily Day 1 - Day 5) + Oxaliplatin (10 mg/kg at Day 2) group. All left-sided tumors were irradiated with 15 Gy at Day 2. Three repeated MR examinations were compared to the MR baseline values established at Day 1. After MR examinations the mice were sacrificed for histological response evaluation. The choice of chemoterapy was based on a clinical patient study currently running at Rikshospitalet-Radiumhospitalet HF, the LARC-RRP (Locally Advanced Rectal Cancer - Radiation Response Prediction) study. In Experiment 1, localized 1H MR spectra were acquired at short (35 ms) and long (144 ms) echo times (TEs) using a single-voxel technique. The metabolite choline is related to tumor growth. The choline peak area relative to the unsuppressed 35 ms TE water area in the same voxel, i.e. the normalized choline ratio, was assessed in all MRS examinations. For both TEs, the choline ratio increased after irradiation, followed by a decrease and a renewed increase 12 days after irradiation. In Experiment 1, statistically significant differences at the 0.1 level were observed between the choline ratios at Day 5 and Day 12 (p = 0.068) for short TE and between the ratios at Day 3 and Day 8 (p = 0.05) for long TE. The change in choline ratio was in accordance with the tumor necrotic fraction (NF) found in histological analyses. Principal component analysis (PCA) revealed a correlation between the score values of ex vivo HR-MAS MR spectra and necrosis. This suggests a correlation between ex vivo and in vivo MRS. In both experiments, the diffusion in the HT29 xenografts varied during treatment. There was a correlation between the amount of necrosis in tumor and the calculated apparent diffusion coefficient (ADC) obtained from DW-MRI examinations. In Experiment 1, statistically significant differences at the 0.1 level were observed between the ADCs at Day 3 and Day 5 (p = 0.05), between Day 5 and Day 12 (p = 0.068), and between Day 8 and Day 12 (p = 0.068). The HT29 xenografts responded to treatment with an initial increase of necrosis due to the short-term effect of treatment, stimulating development of fibrosis. In accordance to the change in choline and ADC, the level of necrosis increased 8 - 12 days after start of treatment, which might correspond to the long-term effect of treatment. The findings in this work shows that in vivo MRS and DW-MRI can be used for non-invasive monitoring of treatment response in an experimental tumor model. This suggests that in vivo MRS and DW-MRI could yield important information about a tumors response to therapy.

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Kyriazi, Stavroula. "The role of diffusion-weighted magnetic resonance imaging in evaluating chemotherapeutic response of metastatic ovarian cancer." Thesis, Institute of Cancer Research (University Of London), 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.543776.

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Rampun, Yambu Andrik. "Computer-aided detection of prostate cancer within the peripheral zone in T2-weighted magnetic resonance imaging." Thesis, Aberystwyth University, 2016. http://hdl.handle.net/2160/51ac4405-5c80-4e72-8f7a-bbc27e8066b2.

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The aim of this research is to develop a computer-aided detection system for prostate cancer within the peripheral zone, based on single modality T2-W Magnetic Resonance Imaging. As the most diagnosed and second leading cause of death from cancer in men, prostate cancer is a significant health problem globally. In fact, considering the deficiencies in current clinical screening methods, there is a need for a rapid development of MRI technologies and computer algorithms to better detect prostate cancer. In this thesis, we developed one unsupervised, and two supervised computer algorithms, using different texture descriptors involving different resolutions, filters, techniques and orientations. For classification purposes, we investigated 11 machine learning algorithms to build predictive models. This thesis also investigated the effects of window sizes for all performance metrics. In the proposed unsupervised method a small number of texture descriptors were used to differentiate benign and malignant regions. Subsequently, the fuzzy c-means clustering algorithm was employed to segment malignant regions. The resulting binary segmentations were then combined to find overlapping regions with the highest probability of being malignant. In contrast, the two supervised methods were based on 215 texture descriptors and textons. Both methods used the same machine learning algorithms in the training and classification phases. To evaluate the performance of the proposed methods, the unsupervised and supervised methods were tested based on 37 (275 MRI images) and 45 (418 MRI images) patients, respectively. The performance evaluations showed that the results of all methods were comparable with the state-of-the-art in the literature in terms of area under the curve, classification accuracy, sensitivity and specificity. The contributions of this thesis are three-fold. First, we developed novel supervised and unsupervised computer-aided detection systems for prostate cancer, which are different from those produced hitherto, in the sense of our methods exploit different combinations of texture descriptors and machine learning algorithms. In fact, this thesis is the first study which has thoroughly investigated textons in prostate cancer detection. Secondly, this thesis made an extensive investigation into the effects of window size, both on the methods and feature's performance itself. Thirdly, we provide an extensive quantitative comparison of the performances of 11 machine learning algorithms and a thorough qualitative comparison between our results and the state-of-the-art in the literature.
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Schneider, Moritz [Verfasser], and Olaf [Akademischer Betreuer] Dietrich. "Incoherent-flow-induced signal decay in diffusion-weighted magnetic resonance imaging / Moritz Schneider ; Betreuer: Olaf Dietrich." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2019. http://d-nb.info/1190563746/34.

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Nordbrøden, Mats. "Optimization of Magnetic Resonance Diffusion Tensor Imaging for Visualization and Quantification of Periprostatic Nerve Fibers." Thesis, KTH, Skolan för teknik och hälsa (STH), 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-179658.

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Prostatectomy, surgical resection of the whole prostate is a common treatment for high- risk prostate cancer. Common side effects include long-time urinary and or erectile dysfunction due to damage inflicted to periprostatic nerves. The aim of this study was to identify an optimal magnetic resonance diffusion tensor imaging protocol for visualization and quantification of these nerves, as pre-surgery visualization may help nerve-sparing surgery. Both scanner filter, parameters for accelerated scan techniques, diffusion-related acquisition parameters and post- processing tractography parameters were investigated. Seven healthy volunteers were scanned with a state-of-art 3 T MRI scanner with varying protocol parameters. Diffusion data were processed and analysed using Matlab and Explore DTI. The resulting protocol recommendation included a normalized scanner filter, a parallel imaging acceleration factor of 2, partial Fourier sampling of 6/8, a right-left phase encoding direction, a b-value of 600 s/mm2, monopolar gradient polarity with applied eddy current correction, four acquisitions of 12 diffusion- sensitizing gradient directions, and a reverse phase encoding approach for correction of geometrical image distortions induced by static field inhomogeneity. For post-processing tractography, the recommended parameters were a lower limit for fractional anisotropy of 0.05, a minimum tract length of 3 centimetres and a maximum turning angle between voxels of 60 degrees. The limited parameter range that was tested and the low number of volunteers can be regarded as limitations to this study. Future work should address these issues. Furthermore, feasibility of periprostatic nerve tracking with the optimized protocol should be tested in a patient study.
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Moribata, Yusaku. "Feasibility of Computed Diffusion Weighted Imaging and Optimization of b-value in Cervical Cancer." 京都大学 (Kyoto University), 2017. http://hdl.handle.net/2433/225457.

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Leclair, Nadine, Gregor Thörmer, Ina Sorge, Lutz Ritter, Volker Schuster, and Franz Wolfgang Hirsch. "Whole-body diffusion-weighted imaging in chronic recurrent multifocal osteomyelitis in children." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-204133.

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Objective: Chronic recurrent multifocal osteomyelitis/ chronic non-bacterial osteomyelitis (CRMO/CNO) is a rare auto-inflammatory disease and typically manifests in terms of musculoskeletal pain. Because of a high frequency of musculoskeletal disorders in children/ adolescents, it can be quite challenging to distinguish CRMO/ CNO from nonspecific musculosketetal pain or from malignancies. The purpose of this study was to evaluate the visibility of CRMO lesions in a whole-body diffusion-weighted imaging (WB-DWI) technique and its potential clinical value to better characterize MR-visible lesions. Materials and methods: Whole-body imaging at 3T was performed in 16 patients (average: 13 years) with confirmed CRMO. The protocol included 2D Short Tau Inversion Recovery (STIR) imaging in coronal and axial orientation as well as diffusion-weighted imaging in axial orientation. Visibility of lesions in DWI and STIR was evaluated by two readers in consensus. The apparent diffusion coefficient (ADC) was measured for every lesion and corresponding reference locations. Results: A total of 33 lesions (on average 2 per patient) visible in STIR and DWI images (b = 800 s/mm2 and ADC maps) were included, predominantly located in the long bones. With a mean value of 1283 mm2/s in lesions, the ADC was significantly higher than in corresponding reference regions (782 mm2/s). By calculating the ratio (lesion to reference), 82% of all lesions showed a relative signal increase of 10% or higher and 76% (25 lesions) showed a signal increase of more than 15%. The median relative signal increase was 69%. Conclusion: This study shows that WB-DWI can be reliably performed in children at 3T and predominantly, the ADC values were substantially elevated in CRMO lesions. WB-DWI in conjunction with clinical data is seen as a promising technique to distinguish benign inflammatory processes (in terms of increased ADC values) from particular malignancies.
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Sarlls, Joelle Elita. "High-resolution Diffusion-weighted Magnetic Resonance Imaging: Development and Application of Novel Radial Fast Spin-echo Acquisitions." Diss., Tucson, Arizona : University of Arizona, 2006. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu%5Fetd%5F1704%5F1%5Fm.pdf&type=application/pdf.

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42

Tokunaga, Koji. "Optimizing b‐values for accurate depiction of pancreatic cancer with tumor-associated pancreatitis on computed diffusion-weighted imaging." Kyoto University, 2020. http://hdl.handle.net/2433/253187.

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43

Wetscherek, Andreas [Verfasser], and Uwe [Akademischer Betreuer] Oelfke. "Magnetic Resonance Diffusion Weighted Imaging: Flow Compensated Intravoxel Incoherent Motion Imaging as a Tool to Probe Microvasculature / Andreas Wetscherek ; Betreuer: Uwe Oelfke." Heidelberg : Universitätsbibliothek Heidelberg, 2013. http://d-nb.info/1177380838/34.

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Pentang, Nadege Gael [Verfasser], Hans-Jörg [Gutachter] Wittsack, and Axel [Gutachter] Görlitz. "Non-Gaussian Analysis Of Diffusion-Weighted Magnetic Resonance Imaging / Nadege Gael Pentang ; Gutachter: Hans-Jörg Wittsack, Axel Görlitz." Düsseldorf : Universitäts- und Landesbibliothek der Heinrich-Heine-Universität Düsseldorf, 2017. http://d-nb.info/1141378566/34.

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45

Minsterová, Alžběta. "Srovnání preklinických DCE-MRI perfusních technik." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2016. http://www.nusl.cz/ntk/nusl-242190.

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This diploma thesis deals with DCE-MRI (Dynamic Contrast-Enhanced Magnetic Resonance Imaging) thus one of the contrast magnetic resonance imaging methods. It describes the principle of conventional continuous DCE-MRI, which uses single bolus of contrast agent and further it focuses on the dual bolus contrast agent techniques, especially the interleaved acquisition. The graphical interface for processing Bruker systems data was made. Synthetic data were used to evaluate the influence of this method on the perfusion parameters estimation. Simulations proved that the further the second bolus is from the first one, the better results are. Simulations of acquisition interruption did not lead to the clear result. However, two statements, which are expected to lead to as good estimation of perfusion parameters as possible, were formulated
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Tziortzi, Andri. "Quantitative dopamine imaging in humans using magnetic resonance and positron emission tomography." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:26b8b4c2-0237-4c40-8c84-9ae818a0dabf.

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Dopamine is an important neurotransmitter that is involved in several human functions such as reward, cognition, emotions and movement. Abnormalities of the neurotransmitter itself, or the dopamine receptors through which it exerts its actions, contribute to a wide range of psychiatric and neurological disorders such as Parkinson’s disease and schizophrenia. Thus far, despite the great interest and extensive research, the exact role of dopamine and the causalities of dopamine related disorders are not fully understood. Here we have developed multimodal imaging methods, to investigate the release of dopamine and the distribution of the dopamine D2-like receptor family in-vivo in healthy humans. We use the [11C]PHNO PET ligand, which enables exploration of dopamine-related parameters in striatal regions, and for the first time in extrastriatal regions, that are known to be associated with distinctive functions and disorders. Our methods involve robust approaches for the manual and automated delineation of these brain regions, in terms of structural and functional organisation, using information from structural and diffusion MRI images. These data have been combined with [11C]PHNO PET data for quantitative dopamine imaging. Our investigation has revealed the distribution and the relative density of the D3R and D2R sites of the dopamine D2-like receptor family, in healthy humans. In addition, we have demonstrated that the release of dopamine has a functional rather than a structural specificity and that the relative densities of the D3R and D2R sites do not drive this specificity. We have also shown that the dopamine D3R receptor is primarily distributed in regions that have a central role in reward and addiction. A finding that supports theories that assigns a primarily limbic role to the D3R.
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KAWAI, HISASHI, KIMINORI BOKURA, SHINJI NAGANAWA, and MASAHIRO YAMAZAKI. "VISUALIZATION OF BRAIN WHITE MATTER TRACTS USING HEAVILY T2-WEIGHTED THREE-DIMENSIONAL FLUID-ATTENUATED INVERSION-RECOVERY MAGNETIC RESONANCE IMAGING." Nagoya University School of Medicine, 2014. http://hdl.handle.net/2237/20547.

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Ma, Jun. "Diffusion- and perfusion-weighted magnetic resonance imaging in patients with acute ischemic stroke: can diffusion/perfusion mismatch predict outcome?" Diss., lmu, 2004. http://nbn-resolving.de/urn:nbn:de:bvb:19-28672.

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Candrák, Matúš. "Zpracování difuzně vážených obrazů pořízených MR tomografem." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2014. http://www.nusl.cz/ntk/nusl-220983.

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The semester thesis describes the basic principles of MRI, methods for measuring diffusion coefficients and creating DWI and DTI images. As a result a practical implementation of program was implemented in Matlab, based on theoretical knowledge of the problem.
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Ghayoor, Ali. "Improved interpretation of brain anatomical structures in magnetic resonance imaging using information from multiple image modalities." Diss., University of Iowa, 2017. https://ir.uiowa.edu/etd/5477.

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This work explores if combining information from multiple Magnetic Resonance Imaging (MRI) modalities provides improved interpretation of brain biological architecture as each MR modality can reveal different characteristics of underlying anatomical structures. Structural MRI provides a means for high-resolution quantitative study of brain morphometry. Diffusion-weighted MR imaging (DWI) allows for low-resolution modeling of diffusivity properties of water molecules. Structural and diffusion-weighted MRI modalities are commonly used for monitoring the biological architecture of the brain in normal development or neurodegenerative disease processes. Structural MRI provides an overall map of brain tissue organization that is useful for identifying distinct anatomical boundaries that define gross organization of the brain. DWI models provide a reflection of the micro-structure of white matter (WM), thereby providing insightful information for measuring localized tissue properties or for generating maps of brain connectivity. Multispectral information from different structural MR modalities can lead to better delineation of anatomical boundaries, but careful considerations should be taken to deal with increased partial volume effects (PVE) when input modalities are provided in different spatial resolutions. Interpretation of diffusion-weighted MRI is strongly limited by its relatively low spatial resolution. PVE's are an inherent consequence of the limited spatial resolution in low-resolution images like DWI. This work develops novel methods to enhance tissue classification by addressing challenges of partial volume effects encountered from multi-modal data that are provided in different spatial resolutions. Additionally, this project addresses PVE in low-resolution DWI scans by introducing a novel super-resolution reconstruction approach that uses prior information from multi-modal structural MR images provided in higher spatial resolution. The major contributions of this work include: 1) Enhancing multi-modal tissue classification by addressing increased PVE when multispectral information come from different spatial resolutions. A novel method was introduced to find pure spatial samples that are not affected by partial volume composition. Once detecting pure samples, we can safely integrate multi-modal information in training/initialization of the classifier for an enhanced segmentation quality. Our method operates in physical spatial domain and is not limited by the constraints of voxel lattice spaces of different input modalities. 2) Enhancing the spatial resolution of DWI scans by introducing a novel method for super-resolution reconstruction of diffusion-weighted imaging data using high biological-resolution information provided by structural MRI data such that the voxel values at tissue boundaries of the reconstructed DWI image will be in agreement with the actual anatomical definitions of morphological data. We used 2D phantom data and 3D simulated multi-modal MR scans for quantitative evaluation of introduced tissue classification approach. The phantom study result demonstrates that the segmentation error rate is reduced when training samples were selected only from the pure samples. Quantitative results using Dice index from 3D simulated MR scans proves that the multi-modal segmentation quality with low-resolution second modality can approach the accuracy of high-resolution multi-modal segmentation when pure samples are incorporated in the training of classifier. We used high-resolution DWI from Human Connectome Project (HCP) as a gold standard for super-resolution reconstruction evaluation to measure the effectiveness of our method to recover high-resolution extrapolations from low-resolution DWI data using three evaluation approaches consisting of brain tractography, rotationally invariant scalars and tensor properties. Our validation demonstrates a significant improvement in the performance of developed approach in providing accurate assessment of brain connectivity and recovering the high-resolution rotationally invariant scalars (RIS) and tensor property measurements when our approach was compared with two common methods in the literature. The novel methods of this work provide important improvements in tools that assist with improving interpretation of brain biological architecture. We demonstrate an increased sensitivity for volumetric and diffusion measures commonly used in clinical trials to advance our understanding of both normal development and disease induced degeneration. The improved sensitivity may lead to a substantial decrease in the necessary sample size required to demonstrate statistical significance and thereby may reduce the cost of future studies or may allow more clinical and observational trials to be performed in parallel.
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