Dissertations / Theses on the topic 'Diffusion Weighted MR Imaging'
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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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MacGillivray, Cathy Carleton University Dissertation Physics. "Diffusion-weighted MR imaging of moving structures using a three echo navigator imaging technique." Ottawa, 1996.
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Coope, David John. "Use of [11C]-methionine PET and diffusion-/perfusion-weighted MR imaging in gliomas." Thesis, University of Manchester, 2010. http://www.manchester.ac.uk/escholar/uk-ac-man-scw:207525.
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Introduction: Low-grade gliomas are a sub-group of primary brain tumours that typically affect young adults and which present specific challenges to conventional diagnostic imaging. They demonstrate a pattern of growth whereby tumour cells infiltrate healthy brain tissue without distortion of the surrounding brain or blood-brain barrier integrity. These features limit the capacity of conventional neuro-imaging strategies to effectively delineate the tumour extent or characterise the degree of 'malignancy'. One solution is to apply multiple imaging modalities to image different aspects of the tumour behaviour, analogous to histological classification based upon changes in mitotic activity, cellular atypia, microvascular proliferation and necrosis. Published information regarding how imaging techniques that address these parameters correlate within the tumour volume is limited. This reflects the technical challenges in acquiring and processing data at an adequate spatial resolution to characterise small but heterogenous tumours. In this thesis, following a series of experiments seeking to optimise the sensitivity and reproducibility of PET analysis in gliomas, a prospective multi-modal neuro-imaging study is presented addressing this need. Methods: Retrospective [11C]-methionine PET (MET PET) data made available through a collaboration with the Max-Planck Institute for Neurological Research in Cologne was carried out first to address the optimal method of analysis of PET data in gliomas. A normal methionine uptake map was created and its use in the analysis of patient scans validated against a conventional approach. Automated methods for delineating the extent of abnormal methionine uptake and identifying the region of peak uptake were developed and evaluated to optimise the reproducibility of the approach. High-resolution MET PET and a comprehensive MRI brain tumour protocol were then acquired prospectively in 20 subjects in Manchester. Detailed analysis of the peak uptake and extent of abnormal tissue defined using PET and MRI modalities including structural, diffusion- and perfusion-weighted techniques was performed. Results: Evaluation of methionine uptake with respect to population normal data, the 'RatioMap' technique, yielded peak uptake measurements that correlated closely with a conventional approach (r = 0.97) but with improved reproducibility. The constrained 3D region-growing algorithm designed to delineate the abnormal region was shown to be reproducible and to generate volumes that correlated with tumour grade. High-resolution multi-modal data in suspected low-grade gliomas demonstrated consistent correlation between peak methionine uptake ratio and peak regional cerebral blood volume (r = 0.85) but with disparity between the location of the maximal uptake regions (mean distance = 11.2mm). Significant correlation was seen between multi-modal MRI and PET ‘tumour’ volumes (r = 0.91) but with substantially larger MRI defined abnormal volumes (ratio = 2.0) including small regions identified as abnormal by multiple MRI parameters but normal on PET imaging. Conclusion: A novel method to enhance the reproducibility of analysis of MET PET images in gliomas has been presented and validated but there remains no single imaging modality capable of fully characterising glioma extent and 'malignancy' non-invasively. Considerable correlation between PET and MRI tumour biomarkers has been demonstrated but there are significant differences between the regions identified as the 'most malignant' for biopsy targeting and the extent of potentially tumour bearing tissue. Combined use of diffusion- and perfusion-weighted MRI parameters can provide results very closely correlated to the PET findings but cannot yet completely replace the use of nuclear medicine techniques. The use of multi-modal approaches to tumour characterisation as demonstrated in this study provides the most effective currently available approach to fully characterise a suspected glioma.
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Tamai, Ken. "The utility of diffusion-weighted MR imaging in the diagnosis of uterine malignancy." Kyoto University, 2008. http://hdl.handle.net/2433/135802.
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Kanao, Shotaro. "Differentiating benign and malignant inflammatory breast lesions: Value of T2 weighted and diffusion weighted MR images." Kyoto University, 2019. http://hdl.handle.net/2433/236592.
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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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Wang, Yanxin. "Hypoxic-ischemic injury in the neonatal rat model prediction of irreversible infarction size by Diffusion Weighted MR Imaging /." Click to view the E-thesis via HKUTO, 2005. http://sunzi.lib.hku.hk/hkuto/record/B35757577.
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Iima, Mami. "Apparent Diffusion Coefficient as an MR Imaging Biomarker of Low-Risk Ductal Carcinoma in Situ: A Pilot Study." Kyoto University, 2014. http://hdl.handle.net/2433/188640.
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Stahle, Jessica Anne. "Diffusion Weighted MR Imaging in the Differentiation between Metastatic and Benign Lymph Nodes in Canine Patients with Head and Neck Disease." Thesis, Virginia Tech, 2016. http://hdl.handle.net/10919/86612.
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In dogs with large primary tumors, regional lymph node involvement or evidence of distant metastasis can have worse prognoses and significantly decreased survival. Lymph node size alone has been shown to be insufficient as a predictor for the accurate clinical staging of some canine neoplasia, including oral malignant melanoma. However, regional lymph nodes of the oral cavity, such as the medial retropharyngeal lymph nodes, are difficult to access for routine sampling. Diffusion weighted magnetic resonance imaging (DWI) has demonstrated the ability to differentiate metastatic from inflammatory/benign lymph nodes in clinical studies with human cancer patients through the calculation of quantitative values of diffusion termed apparent diffusion coefficients (ADC). The objective of this exploratory study was to evaluate DWI and ADC as potential future methods for detecting malignant lymph nodes in dogs with naturally occurring disease. We hypothesized that DWI would identify significantly different ADC values between benign and metastatic lymph nodes in a group of canine patients with head or neck disease.
Our results demonstrated that two of four observers identified a significant difference between the mean ADC values of the benign and metastatic lymph nodes. When data from all four observers were pooled, the difference between the mean ADC values of the benign and metastatic lymph nodes approached but did not reach significance (P-value: 0.0566). Therefore, our hypothesis was not supported. However, DWI does show promise in its ability to differentiate benign from metastatic lymph nodes, and further studies with increased patient numbers are warrantedMaster of Science
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Purvis, Nina Louise. "Classification of breast malignancy using optimised advanced diffusion-weighted imaging, and, Surgical planning for breast tumour resection using MR-guided focused ultrasound." Thesis, University of Hull, 2016. http://hydra.hull.ac.uk/resources/hull:15193.
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Intravoxel Incoherent Motion Imaging (IVIM) is a non-invasive MR-imaging technique that enables the measurement of cellularity and vascularity using diffusion-weighted (DW)-imaging. IVIM has been applied to various cancer types including breast cancer, and is becoming more popular but lacks standardisation. The quantitative parameters; diffusion, D, perfusion fraction, f, and pseudo micro capillary diffusion, D* are thought to be correlated with tumour physiognomies such as proliferation, angiogenesis and heterogeneity. In Part 1 of this thesis, an optimised clinical b-value protocol is produced using a robust statistical method. This optimised protocol and various fitting methodologies are investigated in healthy volunteers, and then the most precise approach is applied in a clinical trial in patients following diagnosis of breast cancer, before treatment, to correlate IVIM parameters with breast cancer grade, histological type and molecular subtype with statistically significant results supporting IVIM’s potential as a non-invasive biomarker for malignancy. Monte Carlo simulations support this clinical application, where real data mean squared errors due to SNR limitations lie within simulated errors. A computed DW-imaging program is also presented to produce better quality images than acquired high b-value images as an adjunct to the optimised IVIM protocol. In Part 2 of this thesis, MR-guided Focused Ultrasound (MRgFUS) is explored as a means to create a pre-surgical template of thermally induced palpable markers to enable a surgeon to resect occult lesions and potentially reduce positive tumour margin status and local recurrence after breast conserving surgery. A surrogate animal model with pseudo lesion is presented, as well as a clinical tool to plan spot markers around a lesion as seen on MRI.
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Filipiak, Isabelle. "IRM de diffusion des fibres blanches cérébrales : développement et validation d'un objet-test." Thesis, Tours, 2014. http://www.theses.fr/2014TOUR3311/document.
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L'imagerie en tenseur de diffusion (DTI) est basée sur la mesure de la mobilité des molécules d'eau permettant l'analyse de la microarchitecture du tissu cérébral. Le trajet des fibres blanches peut être alors reconstruit par des méthodes de tractographie déterministes basées sur la direction principale de la diffusion. Toutefois elle repose sur des outils mathématiques complexes donnant un regard indirect sur les structures anatomiques, et sa validation est un enjeu majeur. Notre objectif a été de concevoir un objet-Test (OT) tri-Dimensionnel permettant la validation de la diffusion dans des faisceaux de fibres imitant l'organisation cérébrale. Cet OT se compose de trois modules: BOITE, SOLUTION, FIBRE réalisés en impression 3D. Il se compose de solutions de glucose et de fibres de dyneema orientées dans les trois orientations de l’espace. Nous nous sommes intéressés au développement d'une méthode de contrôle qualité des mesures quantitatives de diffusion dans le module SOLUTIONDiffusion Tensor Imaging (DTI) is based on the measurement of water diffusion mobility in order to investigate brain microarchitecture and white fiber connectivity. The trajectory of white fibers bundles can be reconstructed by deterministic tractography methods depending on the principal direction of diffusion in tissu. However, tractography consist to complex mathematical algorithms reflecting an indirect visualization of white fibers. Our goal consisted to design a 3D phantom which imitates brain's diffusion properties, offering different degrees of diffusion mobility and imitating the organization of brain fibers. The phantom consists of three components 3D-Printing: BOX, SOLUTION, FIBER. The phantom was composed of various glucose solutions and dyneema synthetical fibers organized in all 3 directions. We developed a quality control of quantitative measurements for the SOLUTION's component. We have lead a comparison of fibers reconstruction between tractography and ground truth in FIBER's component. Results show that : ADC values were ranged on those brain values with glucose solutions; FA
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Ruoss, Kerstin Andrea. "1. Brain development (sulci and gyri) as assessed by MR imaging in preterm and term newborn infants. 2. Germinal matrix hemorrhage and white matter lesions in neonates; correlation of serial ultrasound and early magnetic resonance imaging findings. 3. Diffusion-weighted MRI of middle cerebral artery stroke in a newborn /." Bern, 2002. http://www.stub.unibe.ch/html/haupt/datenbanken/diss/bestell.html.
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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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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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Skare, Stefan. "Optimisation strategies in diffusion tensor MR imaging /." Stockholm, 2002. http://diss.kib.ki.se/2002/91-7349-175-6.
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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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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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Omar, Nur Farhayu. "Diffusion weighted imaging and relaxometry in abdominal organs." Thesis, University of Nottingham, 2016. http://eprints.nottingham.ac.uk/35939/.
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This thesis presents the application of diffusion weighted imaging (DWI) and relaxometry MRI studies in three organs in the abdomen, the kidney, colon and liver. These methods are first applied at 1.5 Tesla in healthy volunteers and patients with Cardiorenal Syndrome (CRS), a clinical condition in which cardiac and renal dysfunctions (RD) coexist. Diffusion parameters are determined using the mono-exponential ADC, bi-exponential IVIM, stretched-exponential and Kurtosis models, as well as diffusion tensor imaging (DTI) in order to assess pathophysiology and structural changes in the kidney. Complementary longitudinal relaxation time (T1) mapping and PC-MRI flow measures are collected for comparison with diffusion parameters. The assessment of the colonic content using T1 measures as a biomarker of water absorption and health is presented in the second study. The main objective of the study was to determine the robustness of bi-exponential model in the fitting of T1 in the colonic contents of ascending colon. T1 measurements of colonic content are made at different positions in the ascending colon, before and after a liquid challenge. The reliability of T1 measurements of colonic content were compared across observers. The heterogeneity in the measurements was evaluated by considering different ROI sizes and locations. The final study is the assessment of liver function associated with Chronic Liver Disease (CLD) using DWI and T1 measurement at 1.5 T and a comparison with histological measures. the Measurements of T1 and diffusion parameters (ADC and IVIM) to stratify fibrosis stage in liver disease are combined with T2* measurement of iron accumulation. The repeatability and reproducibility of this protocol is then tested in the healthy liver using MRI at 3T for the assessment of structural and haemodynamic changes for future studies, with an evaluation of the choice of b-values to inform fitting of the bi-exponential (IVIM) model provided.
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Godley, Keith. "Focused diffusion-weighted imaging in prostate cancer (FODIP)." Thesis, University of East Anglia, 2017. https://ueaeprints.uea.ac.uk/67777/.
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Background: MRI of the prostate is used to detect and localise prostate cancer and diffusion weighted imaging (DWI) is a routine sequence. The purpose of the study was to determine the diagnostic accuracy of high b-value DWI through meta-analyses. Additionally, the aim was to determine the diagnostic accuracy of a novel combined small field-of-view (FOV) and high b-value DWI sequence for detecting and localising prostate cancer. Material and Methods: Meta-analyses of diagnostic test accuracy of high b-value DWI, and T2WI and DWI combined, were performed conforming to the PRISMA statement. A prospective observational diagnostic test accuracy study of 40 patients who underwent 3T MRI with small- (sDWI) and conventional (cDWI) FOV and subsequent radical prostatectomy were included. Two blinded readers assessed the lesion and sectoral-based accuracy of both sequences using radical prostatectomy (RP) specimens as reference standard. Apparent Diffusion Coefficient (ADC) of benign and malignant tissue was assessed. Results: The sensitivity, specificity and area-under-curve (AUC) of the high b-value DWI, and T2WI and DWI meta-analyses were 0.59, 0.92, and 0.92; and 0.68, 0.84 and 0.83, respectively. There were 83 prostate cancers detected in the RP specimens and half of prostate sectors contained tumour. Sensitivity of cDWI alone was significantly higher than sDWI (0.62 vs 0.45, p= < 0.001), but specificity was lower (0.88 vs 0.92, p= < 0.001). The AUC was not significantly different (0.76 vs 0.73, p=0.164). The interobserver reliability of cDWI was substantial (κ = 0.63) and sDWI was moderate (κ = 0.59). The median mean ADC of tumours was significantly lower than non-tumour tissue for both sequences (p= < 0.001). The ADC of tumour was significantly lower with sDWI (960 x 10-6 mm2/sec vs 766 x 10-6 mm2/sec, p= < 0.001). Conclusion: Conventional DWI outperformed small-FOV DWI imaging at lesion detection, but there may be clinical benefit for small-FOV at excluding tumour, particularly in a pre-biopsy population.
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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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Bai, Y. "Correcting for motion between acquisitions in diffusion MR imaging." Thesis, University College London (University of London), 2009. http://discovery.ucl.ac.uk/18690/.
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The diffusion tensor (DT) and other diffusion models assume that each voxel corresponds to the same anatomical location in all the measurements. Movements and distortions violate this assumption and typically the images are realigned before model fitting. We propose a set of model-based methods to improve motion correction and avoid the errors that the traditional method introduces. The new methods are based on a three-step procedure to register DWI datasets, and use different reference images for DWIs with different gradient directions for registration, so the registrations take into account the contrast differences of measurements. Performance of the model-based registration techniques depends critically on outlier rejection. We develop new methods for fitting the diffusion tensor to diffusion MRI measurements in the presence of outliers by drawing on the RANSAC algorithm from computer vision. We compareone popularly used outlier rejection method RESTORE in the diffusion MRI literature with our new method. Then, we combine outlier rejection methods with model-based registration schemes, and compare the performance of motion correction with other methods. After aligning the dataset, we also update diffusion gradients for the registered datasets from both traditional and our methods, according to the transformations used in registrations. We develop and discuss a variety of registration evaluation methods using both synthetic and human-brain diffusion MRI datasets. Experiments demonstrate both quantitative and qualitative improvements using our new model-based methods.
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Mosavi, Firas. "Whole-Body MRI including Diffusion-Weighted Imaging in Oncology." Doctoral thesis, Uppsala universitet, Enheten för radiologi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-209777.
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Cancer is one of the major causes of worldwide mortality. Imaging plays a vital role in the staging, follow-up, and evaluation of therapeutic response in cancer patients. Whole-body (WB) magnetic resonance imaging (MRI), as a non-ionizing imaging technique, is a promising procedure to assess tumor spreading in a single examination. New MRI technological developments now enable the application of diffusion-weighted imaging (DWI) of the entire body. DWI reflects the random motion of water molecules and provides functional information of body tissues. DWI can be quantified with the use of the apparent diffusion coefficient (ADC). The aim of this dissertation was to demonstrate the value of WB MRI including DWI in cancer patients. WB MRI including DWI, 18F-NaF PET/CT, and bone scintigraphy was performed on 49 patients with newly diagnosed, high-risk prostate cancer, for the purpose of detecting bone metastases. WB DWI showed higher specificity, but lower sensitivity compared to 18F-NaF PET/CT. In addition, WB MRI including DWI, and CT of the chest and abdomen was performed in 23 patients with malignant melanoma. We concluded that WB MRI could not completely supplant CT for the staging of malignant melanoma, especially with respect to the detection of lesions in the chest region. In this study, WB MRI and DWI were able to detect more bone lesions compared to CT, and showed several lesions outside the CT field of view, reinforcing the advantage of whole-body examination. WB MRI, including DWI, was performed in 71 patients with testicular cancer. This modality demonstrated its feasibility for use in the follow-up of such patients. WB MRI, including DWI, and 18F-FDG PET-CT, were carried out in 50 patients with malignant lymphoma. Both these imaging modalities proved to be promising approaches for predicting clinical outcomes and discriminating between different subtypes of lymphomas. In conclusion, WB MRI, including DWI, is an evolving technique that is continuing to undergo technical refinement. Standardization of image acquisition and analysis will be invaluable, allowing for more accurate comparison between studies, and widespread application of this technique in clinical practice. Both WB MRI, including DWI and PET/CT, have their particular strengths and weaknesses in the evaluation of metastatic disease. DWI and PET/CT are different functional techniques, so that combinations of these techniques may provide complementary and more comprehensive information of tumor tissue.
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Nunes, Rita G. "Development of diffusion-weighted imaging at high magnetic field." Thesis, University of Oxford, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.424867.
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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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Nguyen, Quyen. "Quantitative diffusion weighted imaging : techniques and applications to perinatal asphyxia." Thesis, University College London (University of London), 2001. http://discovery.ucl.ac.uk/1382401/.
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This thesis describes the results of a study to investigate early cerebral changes in a piglet model of perinatal asphyxia using quantitative diffusion-weighted imaging (DWI) and subsequent work to develop a robust DWI technique to enable similar studies to be performed in neonates. 31Phophorus magnetic resonance spectroscopy and quantitative diffusion and T2 imaging of the cerebrum were performed in a piglet model of perinatal asphyxia. A significant decline in the ratio of phosphocreatine to inorganic phosphate concentrations ([PCr]/[Pi]) was observed during the 48 hours following the transient hypoxicischaemic (H-I) insult. The global directionally averaged apparent diffusion coefficient (ADCav) also declined significantly during the same period and a strong correlation between the [PCr]/[Pi] and ADCav was found. Strong regional and temporal variations in the cerebral response were observed following the H-I insult. In the basal ganglia and parasagittal cortex, significant decline in ADCs was seen approximately 8 hours after the H-I insult. In the thalamus, internal capsule, periventricular white matter and medial cortex, significant ADCs decline was not observed until 32 hours following the H-I insult. A significant T2 increase was observed in the internal capsule but not in the other regions of interest. To enable clinical DWI to be performed in neonates a novel `reacquisition' technique that overcomes the problem of motion artefact in DWI is presented. The reacquisition technique involves the automatic detection and reacquisition of motion-corrupted data in real-time. Computer simulations were used to demonstrate that motion-corrupted data may be detected accurately and reacquired in a time efficient manner. The reacquisition technique was implemented on a Bruker AVANCE scanner in combination with a spinecho 2DFT DWI sequence and an interleaved EPI DWI sequence. The effectiveness of the technique was demonstrated with both a computer-controlled motion phantom and neonates from an ongoing study of perinatal asphyxia.
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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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Domenig, Claudia. "Development and evaluation of MR imaging techniques for quantitative diffusion imaging of the human pelvis." Thesis, University of Surrey, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.273242.
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Hering, Jan [Verfasser], and Bernd [Akademischer Betreuer] Jähne. "Robust Motion and Distortion Correction of Diffusion-Weighted MR Images / Jan Hering ; Betreuer: Bernd Jähne." Heidelberg : Universitätsbibliothek Heidelberg, 2016. http://d-nb.info/1180737466/34.
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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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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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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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Rapacchi, Stanislas. "Low b-values diffusion weighted imaging of the in vivo human heart." Thesis, Lyon 1, 2011. http://www.theses.fr/2011LYO10012/document.
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L'Imagerie par Résonance Magnétique pondérée en Diffusion (IRM-D) permet l'accès à l'information structurelle des tissus au travers de la lecture du mouvement brownien des molécules d'eau. Ses applications sont nombreuses en imagerie cérébrale, tant en milieu clinique qu'en recherche. Néanmoins le mouvement physiologique créé une perte de signal supplémentaire au cours de l'encodage de la diffusion. Cette perte de signal liée au mouvement limite les applications de l'IRM-D quant à l'imagerie cardiaque. L'utilisation de faibles valeurs de pondération (b) réduit cette sensibilité mais permet seulement l'imagerie du mouvement incohérent intra-voxel (IVIM) qui contient la circulation sanguine et la diffusion des molécules d'eau. L'imagerie IVIM possède pourtant de nombreuses applications en IRM de l'abdomen, depuis la caractérisation tissulaire à la quantification de la perfusion, mais reste inexplorée pour l'imagerie du coeur. Mon travail de thèse correspond à l'évaluation des conditions d'application de l'IRM-D à faibles valeurs de b pour le coeur humain, afin de proposer des contributions méthodologiques et d'appliquer les techniques développées expérimentalement. Nous avons identifié le mouvement cardiaque comme une des sources majeures de perte de signal. Bien que le mouvement global puisse être corrigé par un recalage non-rigide, la perte de signal induite par le mouvement perdure et empêche l'analyse précise par IRM-D du myocarde. L'étude de cette perte de signal chez un volontaire a fourni une fenêtre temporelle durable où le mouvement cardiaque est au minimum en diastole. Au sein de cette fenêtre optimale, la fluctuation de l'intensité atteste d'un mouvement variable résiduel. Une solution de répéter les acquisitions avec un déclenchement décalé dans le temps permet la capture des minimas du mouvement, c.-à-d. des maximas d'intensité en IRM-D. La projection du maximum d'intensité dans le temps (TMIP) permet ensuite de récupérer des images pondérées en diffusion avec un minimum de perte de signal lié au mouvement. Nous avons développé et évalué différentes séquences d'acquisition combinées avec TMIP : la séquence d'imagerie écho-planaire classique par écho de spin (SE-EPI) peut être adaptée mais souffre du repliement d'image ; une séquence Carr-Purcell-Meiboom-Gill combinée avec une préparation d'encodage de diffusion est plus robuste aux distorsions spatiales mais des artefacts de bandes noires empêchent son applicabilité ; finalement une séquence double-SE-EPI compensant les courants de Foucault et pleinement optimisée produit des images IRM-D moins artefactées. Avec cette séquence, l'IRM-D-TMIP permet la réduction significative de la perte de signal liée au mouvement pour l'imagerie cardiaque pondérée en diffusion. L'inconvénient avec TMIP vient de l'amplification du bruit positif d'intensité. Afin de compenser cette sensibilité du TMIP, nous séparons le bruit d'intensité des fluctuations lentes liées au mouvement grâce à une nouvelle approche basée sur l'analyse en composantes principales (PCA). La décomposition préserve les détails anatomiques tout en augmentant les rapports signal et contraste-à-bruit (SNR, CNR). Avec l'IRM-D-PCATMIP, nous augmentons à la fois l'intensité finale et la qualité d'image (SNR) en théorie et expérimentalement. Les bénéfices ont été quantifiés en simulation avant d'être validés sur des volontaires. De plus la technique a montré des résultats reproductibles sur des patients post-infarctus aigue du myocarde, avec un contraste cohérent avec la position et l'étendue de la zone pathologique. Contrairement à l'imagerie cérébrale, l'imagerie IRM-D par faibles valeurs de pondération in vivo doit être différentiée des analyses IRM-D ex-vivo. Ainsi l'IRM-D-PCATMIP offre une technique sans injection pour l'exploration du myocarde par imagerie IVIM. Les premiers résultats sont encourageants pour envisager l'application sur un modèle expérimental d'une maladie cardiovasculaire [etc...]Diffusion weighted magnetic resonance imaging (DW-MRI, or DWI) enables the access to the structural information of body tissues through the reading of water molecules Brownian motion. Its applications are many in brain imaging, from clinical practice to research. However physiological motion induces an additional signal-loss when diffusion encoding is applied. This motion-induced signal-loss limits greatly its applications in cardiac imaging. Using low diffusion-weighting values (b) DWI reduces this sensitivity but permits only the imaging of intravoxel incoherent motion (IVIM), which combines both water diffusion and perfusion. IVIM imaging has many applications in body MRI, from tissue characterization to perfusion quantification but remains unexplored for the imaging of the heart. The purpose of this work was to evaluate the context of low b-values DWI imaging of the heart, propose methodological contributions and then apply the developed techniques experimentally. We identified cardiac motion as one of the major sources of motion-induced signal loss. Although bulk motion can be corrected with a non-rigid registration algorithm, additional signal-loss remains uncorrected for and prevents accurate DWI of the myocardium. The study of diffusion-weighted signal-loss induced by cardiac motion in a volunteer provided a time-window when motion is at minimum in diastole. Within this optimal time-window, fluctuation of intensity attests of variable remaining physiological motion. A solution to repeat acquisition with shifted trigger-times ease the capture of motion amplitude minima, i.e. DWI-intensity maxima. Temporal maximum intensity projection (TMIP) finally retrieves diffusion weighted images of minimal motion-induced signal-loss. We evaluated various attempts of sequence development with TMIP: usual spin-echo echo-planar imaging (se-EPI) sequence can be improved but suffers aliasing issues; a balanced steady-state free-precession (b-SSFP) combined with a diffusion preparation is more robust to spatial distortions but typical banding artifacts prevent its applicability; finally a state-of-the-art double-spin-echo EPI sequence produces less artifacted DWI results. With this sequence, TMIP-DWI proves to significantly reduce motion-induced signal-loss in the imaging of the myocardium. The drawback with TMIP comes from noise spikes that can easily be highlighted. To compensate for TMIP noise sensitivity, we separated noise spikes from smooth fluctuation of intensity using a novel approach based on localized principal component analysis (PCA). The decomposition was made so as to preserve anatomical features while increasing signal and contrast to noise ratios (SNR, CNR). With PCATMIP-DWI, both signal-intensity and SNR are increased theoretically and experimentally. Benefits were quantified in a simulation before being validated in volunteers. Additionally the technique showed reproducible results in a sample of acute myocardial infarction (AMI) patients, with a contrast matching the extent and location of the injured area. Contrarily to brain imaging, in vivo low b-values DWI should be differentiated from ex vivo DWI pure diffusion measurements. Thus PCATMIP-DWI might provide an injection-free technique for exploring cardiac IVIM imaging. Early results encourage the exploration of PCATMIP-DWI in an experimental model of cardiac diseases. Moreover the access to higher b values would permit the study of the full IVIM model for the human heart that retrieves and separates both perfusion and diffusion information
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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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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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Theilmann, Rebecca Jean. "High-resolution diffusion imaging with DIFRAD-FSE (diffusion-weighted radial acquisition with fast spin echo) MRI." Diss., The University of Arizona, 2001. http://hdl.handle.net/10150/284332.
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A novel MRI method, DIFRAD-FSE (D̲i̲f̲fusion with R̲adial A̲cquisition of D̲ata with F̲ast S̲pin-E̲cho) is presented that enables rapid, high-resolution, multi-shot diffusion-weighted MRI without significant artifacts due to motion. Following a diffusion-weighted spin-echo preparation, multiple radial lines of Fourier data are acquired using spin-echo refocusing. Data can be acquired in either 2D or 3D Fourier space. Motion correction is accomplished via one of four correction techniques: phase correction, shift correction, a combination of the phase and shift correction, or magnitude. Images from a radial data set are reconstructed with filtered back projection reconstruction. Results from human brain imaging will demonstrate the ability of DIFRAD-FSE to acquire high-resolution images without significant artifacts due to motion in both 2D and 3D. Results from liver and heart imaging demonstrate the versatility of the 2D DIFRAD-FSE.
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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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Schob, Stefan, Jonas Meyer, Matthias Gawlitza, Clara Frydrychowicz, Wolf Müller, Matthias Preuss, Lionel Bure, Ulf Quäschling, Karl-Titus Hoffmann, and Alexey Surov. "Diffusion-weighted MRI reflects proliferative activity in primary CNS lymphoma." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-210909.
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Purpose: To investigate if apparent diffusion coefficient (ADC) values within primary central nervous system lymphoma correlate with cellularity and proliferative activity in corresponding histological samples.
Materials and Methods: Echo-planar diffusion-weighted magnetic resonance images obtained from 21 patients with primary central nervous system lymphoma were reviewed retrospectively. Regions of interest were drawn on ADC maps corresponding to the contrast enhancing parts of the tumors. Biopsies from all 21 patients were histologically analyzed. Nuclei count, total nuclei area and average nuclei area were measured. The proliferation index was estimated as Ki-67 positive nuclei divided by total number of nuclei. Correlations of ADC values and histopathologic parameters were determined statistically. Results: Ki-67 staining revealed a statistically significant correlation with ADCmin (r = -0.454, p = 0.038), ADCmean (r = -0.546, p = 0.010) and ADCmax (r = -0.515, p = 0.017). Furthermore, ADCmean correlated in a statistically significant manner with total nucleic area (r = -0.500, p = 0.021). Conclusion: Low ADCmin, ADCmean and ADCmax values reflect a high proliferative activity of primary cental nervous system lymphoma. Low ADCmean values—in concordance with several
previously published studies—indicate an increased cellularity within the tumor.
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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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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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Gong, Nanjie, and 龔南杰. "Probing tissue microstructural changes in neurodegenerative processes using non-gaussian diffusion MR imaging." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2014. http://hdl.handle.net/10722/208583.
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Development of non-invasive imaging biomarkers sensitive to microstructural organization is crucial for deepening our understanding of mechanisms underlying neurodegenerative processes such as aging and further improving early diagnosis and monitoring of neurodegenerative disease such as Alzheimer’s disease (AD) and amnestic mild cognitive impairment (MCI). The diffusional kurtosis imaging (DKI) is an extension of conventional diffusion tensor imaging. It is hypothesized that DKI will provide complementary information to conventional diffusivity metrics in a new dimension that will more comprehensively capture microstructural changes in anisotropic white matter tracts and particularly in relatively isotropic tissues such as gray matter during neurodegenerative processing of aging, MCI and AD and probably improve the early diagnosis of the diseases.
Firstly, DKI method and a white-matter model that provided metrics of explicit neurobiological interpretations were applied on healthy participants. In white matter tracts, age-related degenerations appeared to be broadly driven by axonal loss. Demyelination may also be a major driving mechanism, although confined to the anterior brain. In terms of deep gray matter, higher mean kurtosis (MK) and fractional anisotropy (FA) in the globus pallidus, substantia nigra, and red nucleus reflected higher microstructural complexity and directionality compared with the putamen, caudate nucleus, and thalamus. In particular, unique age-related positive correlations for FA, MK, and radial kurtosis (KR) in the putamen opposite to those in other regions were observed.
Secondly, to verify the speculation that iron deposition could be one probable underlying mechanism driving changes in microstructure, another advance MRI technique of quantitative susceptibility mapping (QSM) was also used in healthy participants. Significant age-related increases of iron were observed in the putamen, red nucleus, substantia nigra, and caudate nucleus. Putamen exhibited the highest rate of iron accumulation with aging, which was nearly twice of the rates in substantia nigra and caudate nucleus. Significant positive correlations between susceptibility value and diffusion measurements were observed for FA and MK in the putamen as well as FA in the red nucleus.
Thirdly, whether DKI metrics could serve as imaging biomarkers to indicate the severity of cognitive deficiency for AD and MCI was investigated. In AD, significantly increased diffusivity and decreased kurtosis parameters were observed in both white and gray matter of the parietal and occipital lobes as compared to MCI. Significantly decreased FA was also observed in the white matter of these lobes in AD. With the exception of FA and KR, all the other five DKI metrics exhibited significant correlations with mini-mental state examination score in both white and gray matter.
Lastly, DKI metrics were compared against volumetry for diagnosis of AD and MCI. In AD vs. aMCI, although no significant difference of either FA or MD was observed in white matter tracts, it is encouraging to note that MK captured loss of microstructural complexity in the superior longitudinal fasciculus and internal capsule. MK in the putamen showed the highest power that outperformed volume of the hippocampus for discriminating AD from normal. Besides, FA in the putamen showed the second highest power for discriminating aMCI from normal.published_or_final_version
Diagnostic Radiology
Doctoral
Doctor of Philosophy
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Plicco, Chiara. "Le metodiche di Diffusion Weighted Imaging per la caratterizzazione della malattia policistica renale." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amslaurea.unibo.it/11202/.
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La tecnica di Diffusion Weighted Imaging (DWI) si basa sullo studio del moto diffusivo delle molecole d’acqua nei tessuti biologici ed è in grado di fornire informazioni sulla struttura dei tessuti e sulla presenza di eventuali alterazioni patologiche. Il più recente sviluppo della DWI è rappresentato dal Diffusion Tensor Imaging (DTI), tecnica che permette di determinare non solo l’entità, ma anche le direzioni principali della diffusione. Negli ultimi anni, grazie ai progressi nella tecnica di risonanza magnetica, l’imaging di diffusione è stato anche applicato ad altri distretti anatomici tra cui quello renale, per sfruttarne le potenzialità diagnostiche. Tuttavia, pochi sono ancora gli studi relativi all’applicazione delle metodiche di diffusione per la valutazione della malattia policistica renale autosomica dominante (ADPKD). ADPKD è una delle malattie ereditarie più comuni ed è la principale causa genetica di insufficienza renale dell’adulto. La caratteristica principale consiste nella formazione di cisti in entrambi i reni, che progressivamente aumentano in numero e dimensioni fino a causare la perdita della funzionalità renale nella metà circa dei pazienti. Ad oggi non sono disponibili terapie capaci di arrestare o rallentare l’evoluzione di ADPKD; è possibile controllare le complicanze per evitare che costituiscano componenti peggiorative. Il lavoro di tesi nasce dalla volontà di indagare se la tecnica dell’imaging di diffusione possa essere utile per fornire informazioni sullo stato della malattia e sul suo grado di avanzamento. L’analisi di studio è concentrata sul calcolo del coefficiente di diffusione apparente (ADC), derivato dalle immagini DWI e valutato nella regione della midollare. L’obiettivo di questo lavoro è verificare se tale valore di ADC sia in grado di caratterizzare la malattia policistica renale e possa essere utilizzato in ambito clinico-diagnostico come indicatore prognostico nella progressione di questa patologia.
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Yang, Sheng Yang. "A Simplified Estimation Model for Two Crossing Fiber Orientations in Diffusion Weighted Imaging." Case Western Reserve University School of Graduate Studies / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=case1531760896809294.
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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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Coad, Bethany. "Neurocognitive networks for social cognition : insights from diffusion weighted imaging and frontotemporal dementia." Thesis, Cardiff University, 2017. http://orca.cf.ac.uk/111503/.
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Empathy is a complex and multicomponent social cognitive function. It is underpinned by large-scale neurocognitive networks, the precise cognitive and neural structure of which remains debated. Despite this, relatively little work has considered the cognitive or neural components of empathy at the network-level. Here I present work using diffusion weighted magnetic resonance imaging (DWI) in healthy adults, and cognitive and behavioural assessment in a relatively rare form of dementia, the behavioural variant of frontotemporal dementia (bvFTD). Using these methods I explore: (a) the relationship between the microstructural properties of white matter tracts that mediate connectivity between distinct neurocognitive networks and separable cognitive components of empathic cognition (b) the cognitive and behavioural consequences of perturbation to neurocognitive networks in dementia. BvFTD is of interest here as it appears to preferentially target neural networks that support socioemotional processing. In chapters 2 and 3, evidence regarding the white matter structures that are affected by bvFTD guides investigations of the relationship between the microstructural properties of specific white matter tracts and social cognitive functioning in the healthy adult brain. In these chapters, I show that, in young healthy adults, two white matter pathways, sensitive to early changes in bvFTD, the Uncinate fasciculus (UF) and the cingulum bundle (CB), are related to individual differences in two components of empathic functioning, respectively: facial emotion decoding and mentalising. In chapter 4 I show the dissociation of performance on tasks assessing these cognitive functions in an individual with early bvFTD. I highlight the sensitivity and potential clinical utility of tasks assessing literary fiction-based mentalising. In Chapter 5 I present a detailed qualitative description of social cognitive change in frontotemporal dementia (FTD), from the perspective of family members. I consider what such detailed descriptions of everyday behaviour may tell us about the cognitive underpinnings of complex social behaviour. The findings of this thesis further our understanding of the dissociable neurocognitive networks that support empathic functioning, including their structural underpinnings and the behavioural consequences of their perturbation. In the general discussion, I consider the implications of this work for our understanding of social cognitive functioning and bvFTD.
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Nakajima, Satoshi. "Primary central nervous system lymphoma and glioblastoma: differentiation using dynamic susceptibility-contrast perfusion-weighted imaging, diffusion-weighted imaging, and 18F-fluorodeoxyglucose positron emission tomography." Kyoto University, 2016. http://hdl.handle.net/2433/204580.
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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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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
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Tozer, Daniel John. "In vivo diffusion-weighted studies in the prostate and breast using echo-planar imaging." Thesis, University of Hull, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.272008.
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Forbes, K. P. N. "Diffusion-weighted imaging in brain ischaemia : clinical studies and assessment of a novel technique." Thesis, University of Cambridge, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.599098.
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Yang, Jia [Verfasser], and Christopher [Akademischer Betreuer] Nimsky. "Investigation on the optimization approaches of diffusion weighted imaging / Jia Yang ; Betreuer: Christopher Nimsky." Marburg : Philipps-Universität Marburg, 2019. http://d-nb.info/1198401613/34.
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