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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

Magnetic resonance renography: optimization and clinical orientation

Priester, Jacobus Adriaan de. January 1900 (has links)
Proefschrift Universiteit Maastricht. / Auteursnaam op omslag: Koo de Priester. Met lit. opg. - Met samenvatting in het Nederlands.
42

Magnetic resonance imaging investigations of directed influence in the brain methodological contributions and application to task switching studies /

Roebroeck, Alard Franc. January 2006 (has links)
Proefschrift Maastricht. / Lit. opg. - Met een samenvatting in het Nederlands.
43

The role of magnetic field gradients in nuclear magnetic resonance

Luck, Stanley David January 1986 (has links)
A high resolution NMR probe was modified with gradient coils (31 mm diameter) for the measurement of translational diffusion and for microscopic imaging, and a larger set of gradient coils (15 cm diameter) was constructed for surface coil diffusion measurements. The magnitudes of the gradients produced by these coils were determined from the linewidths and lineshapes of gradient spectra. In diffusion experiments using the pulsed gradient method of Stejskal and Tanner, induced eddy currents and slow variation of the magnetic field at the sample interfered with measurements at short echo times. For these experiments the known diffusion coefficient of water was used to determine the effective gradient in each experiment. The diffusion coefficient of acrylonitrile was measured from the decay of single, double and triple quantum echoes using a modified pulsed field gradient spin echo pulse sequence. In the second part of this thesis, three examples of living systems were studied. The first involved the application of pulsed gradient spin echo measurements to characterize the motion of water and lipid, in-vivo, in human forearm. Spin echo spectra from human forearm gave a water signal that was attributed to extracellular water because of relatively long spin-spin relaxation time (0.8 s) compared to that of intracellular water (20-30 ms). Comparison of the diffusivity of water, from experiments at two different echo times suggest that the major part of the motion of water, in-vivo, was due to directionally randomized bulk flow rather than molecular diffusion. The second application involved the chemical shift resolved mapping of the proton distribution, in one-dimension, along the anteroposterior direction, of pupae of the Douglas-fir cone moth Barbara colfaxiana. Proton distribution maps showed that the distribution of the aqueous fluid depended upon the vertical orientation, head pointing upward or downward, of the pupae. Finally, two dimensional images of mature caps of the marine alga Acetabularia mediterranea were obtained using the normal spin echo sequence as well as with T₁, T₂ and diffusion contrasting. D₂O—contrasting was obtained by briefly submerging the caps in D₂O. All of these images showed features resembling the radial structure of the caps. The resolution was estimated by comparison with microscopic views of the caps and was found to be 0.1 mm, determined as the smallest distinguishable feature in the image. / Science, Faculty of / Chemistry, Department of / Graduate
44

Non-medical applications of imaging techniques : multi-dimensional NMR imaging

Rajanayagam, Vasanthakumar January 1986 (has links)
The work described in this thesis concentrates on two aspects of Proton NMR imaging: development and evaluation of new/old experimental sequences and application of those techniques to study some non-medical systems that are of industrial importance. Two-dimensional Fourier transform spin warp imaging technique has been evaluated. Importantly, the adaptation of a conventional high resolution spectrometer to perform imaging has been demonstrated with means of "phantoms". This includes calibration of magnetic field gradients, mapping the static magnetic field and radiofrequency field distributions and intensity measurements related to proton spin densities. In addition, a preliminary study describes microscopic imaging of glass capillary tube phantoms containing water. Several different sequences related to Chemical Shift imaging including the one developed during the study have been described. A brief insight into chemical shift artifacts as well as some experimental methods of minimizing some of them have also been presented. The potential of NMR imaging to study non-medical systems has been explored in three different areas of interest: Chromatography columns. Porous rock samples and Wood samples. A variety of NMR imaging sequences have been used to study some interesting and challenging features of these systems which clearly extends the scope of NMR imaging science. / Science, Faculty of / Chemistry, Department of / Graduate
45

Numerical and experimental modeling of atherosclerosis related to MRI

Bernsdorf, Stefan January 1998 (has links)
Bibliography: [appendix A-1 to A-2]. / This thesis was motivated by the idea of employing non-invasive investigations of atherosclerosis using Magnetic Resonance Imaging (MRI). MRI has the advantage of being able to detect atheroma in blood vessels with no risk to the patient but is still limited in its application to large blood vessels by the low geometrical resolution obtainable. The capability of MRI to measure velocities as well leads to the idea of correlating atheroma dimensions with measured velocities downstream of the blockage. This thesis makes a first step towards obtaining results that can be applied in investigations of atherosclerosis employing MRI. The fluid dynamics of arterial blood flow, the medical procedure of diagnosing and treating atherosclerotic diseases, and the physical principle of MRI are investigated to find out "if' and "how" the correlation between a blockage and the resulting downstream velocities can contribute to the diagnosis of atheroma. Parallel to this background research, experimental and numerical modeling of atheroma is carried out. These two approaches use identical geometrical and fluid parameters to enable a direct validation of the results. An experimental test-rig is designed. Experiments with different types of blockages are performed. The measured flow parameters are pressure and velocity profiles in a crosssection of the modeled artery. A commercial software package is employed for the numerical simulation of blockages with similar geometries to those used in the experiments. The pressure and absolute velocities are again the derived parameters. Both approaches are validated with analytical results obtainable for flow without any blockages. Blockages are then inserted and the results are compared and analyzed for their potential to contribute to the medical application. The results obtained with the two models give good correspondence. The transitional length of the laminar pipe flow corresponds very well to the expectations. A laminar velocity profile is completely built up before the fluid enters a blockage. Blockages with a small flow area cause a high peak velocity and a large wake. Blockages that slightly reduce the flow area have only a small influence on the flow. The length of a blockage has only a secondary influence on the downstream velocity distribution, while the influence of the surface roughness of the blockage is small. The peak velocities and pressure loss caused by the different blockages give good correlation. The prediction of the diameter of the blockage from peak velocities measured with MRI is an improvement on that which is possible from the theory only. In particular, the results obtained in this thesis show that the true maximum velocities are significantly lower than those obtained with theoretical predictions. The change in the velocity profiles, due to angioplasty, is shown in a simplified form with the models. Typical values of reduced areas before and after such surgery, where the atheroma is squeezed against the arterial walls, are analysed. The influence of the post-surgery blockage on the flow is very small, while the pre-surgery blockage shows a dominant influence. A prominent wake exists downstream of a highly reduced flow area, and high velocities occur. A wake is a potential risk area for atherosclerosis, as low shear rates and high turbulence intensities are possible. The blockage with the less reduced area has almost no influence on the flow, and a wake is hardly formed. The influence of different shapes of atheroma, while having a similar reduced area, is also demonstrated. The perfectly symmetrical blockage has less negative influence on the flow than one which is highly asymmetrical. The asymmetrical blockage causes a larger wake and higher maximum velocities.
46

Functional magnetic resonance imaging (FMRI) of brain and cervical spinal cord

吳文卓, Ng, Man-cheuk. January 2007 (has links)
published_or_final_version / abstract / Orthopaedics and Traumatology / Doctoral / Doctor of Philosophy
47

Plasticity of human brain networks as revealed by functional magnetic resonance imaging

Yuen, Sung-lai., 袁崇禮. January 2007 (has links)
The best for PhD thesis in the Faculties of Arts, Architecture, Business & Economics, Education, Law and Social Sciences (Universityof Hong Kong), Li Ka Shing prize, 2006-2007 / published_or_final_version / abstract / Psychology / Doctoral / Doctor of Philosophy
48

Synthetic MRI for visualization of quantitative MRI

Peterson, Erika January 2013 (has links)
Magnetic resonance imaging (MRI) is an imaging technique that is used in hospitals worldwide. The images are acquired through the use of an MRI scanner and the clinical information is provided through the image contrast, which is based on the magnetic properties in biological tissue. By altering the scanner settings, images with different contrast properties can be obtained. Conventional MRI is a qualitative imaging technique and no absolute measurements are performed. At Center for Medical Imaging and Visualization (CMIV) researchers are developing a new MRI technique named synthetic MRI (SyMRI). SyMRI is based on quantitative measurements of data and absolute values of the magnetic properties of the biological tissue can be obtained. The purpose of this master thesis has been to take the development of SyMRI a step further by developing and implementing a visualization studio for SyMRI imaging of the human brain. The software, SyMRI Brain Studio, is intended to be used in clinical routine. Input from radiologists was used to evaluate the imaging technique and the software. Additionally, the requirements of the radiologists were converted into technical specifications for the imaging technique and SyMRI Brain Studio. Additionally, validation of the potential in terms of replacing conventional MRI with SyMRI Brain Studio was performed. The work resulted in visualization software that provides a solid formation for the future development of SyMRI Brain Studio into a clinical tool that can be used for validation and research purposes. A list of suggestions for the future developments is also presented. Future clinical evaluation, technical improvements and research are required in order to estimate the potential of SyMRI and to introduce the technique as a generally used clinical tool.
49

Asynchronous neuro-osseous growth in adolescent idiopathic scoliosis associated with anatomical changes: new approach with morphological and functional magnetic resonance imaging studies. / CUHK electronic theses & dissertations collection

January 2007 (has links)
For the nervous system, there is evidence of relative shortening of the spinal cord, reflected by both reduced cord length to vertebral column ratio and a change in cross-sectional morphology of the cord. The cerebellar tonsils are low-lying in AIS subjects while significant regional volume differences in the brain are also evident between AIS subjects and controls. / From the results of this series of study, AIS girls are found to have morphological difference in multiple aspects when compared with age- and sex-matched normal controls. / Idiopathic scoliosis is a common worldwide problem and has been treated for many decades; however, there still remain uncertain areas about this disorder. Its involvement and impact on different parts of the human body remain underestimated due to lack of technology in imaging for objective assessment in the past. / In the skeletal system, AIS girls have generalized osteopenia and abnormal growth of the appendiceal skeleton. For the axial skeleton, abnormal ossification patterns have been found affecting both the longitudinal growth and axial growth pattern of the vertebral column. There is overgrowth of the anterior vertebral column, reversed asymmetry of the neural arch and smaller pedicle at the concavity of the scoliotic curve in AIS, suggestive of asynchronous growth between membraneous and endochondral ossifications. In the skull, both calvarium and basicranium are found have regional difference (including foramen magnum) between AIS subjects and controls, which is again probably reflecting a systemic process of asynchronous growth between membraneous and endochondral ossification. / It was concluded that the hypothesis "In adolescent idiopathic scoliosis, advanced magnetic resonance imaging techniques can be used to identify systemic features which are suggestive of asynchronous neuro-osseous growth of the disorder" was confirmed. (Abstract shortened by UMI.) / Taking together, the abnormalities in the skeletal system and nervous system are likely to be inter-related and reflecting a systemic process of asynchronous neuro-osseous growth. The above findings help to explain a number of well documented neurological abnormalities in AIS: Anatomically, there is increased incidence of Chiari malformation and syringomyelia in AIS subjects, while functionally, abnormal somatosensory evoked potential (SSEP) results, impaired postural balance, poor performance on combined visual and proprioceptive testing and spatial orientation testing as well as reports of abnormal nystagmus response to caloric testing are known to be associated with AIS. / The advances in imaging technique and image analysis technology have provided a novel approach for the understanding of the phenotypic presentation of neuro-osseous changes in AIS subjects as compared with normal controls. Dynamic imaging also assists in functional assessment of pulmonary function and respiratory mechanism in AIS subjects. / The hypothesis to be tested in this series of studies is: "In adolescent idiopathic scoliosis, advanced magnetic resonance imaging techniques can be used to identify systemic features which are suggestive of asynchronous neuro-osseous growth of the disorder". This thesis was based on a series of eight studies which were aimed to explore the "unknown" anatomical features in the skeletal and neural systems in AIS by the application of new advanced technique of MR imaging and sophisticated image analysis programs. / We are the first group who has undertaken a comprehensive morphological assessment of the skeletal and nervous systems in AIS subjects based on imaging findings which have not been reported previously. For the first time in literature, the spinal cord and vertebral column, brain and skull were thoroughly analyzed in AIS subjects and compared with age- and sex-matched normal controls. Detailed correlations with clinical information, neurological tests have also been made. As an appendix, MR imaging findings of the pulmonary system in AIS, including the lung, chest wall and diaphragms are also presented at the end of the thesis. / Chu Chiu-wing, Winnie. / Source: Dissertation Abstracts International, Volume: 69-02, Section: B, page: 0976. / Thesis (M.D.)--Chinese University of Hong Kong, 2007. / Includes bibliographical references (p. 248-267). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / School code: 1307.
50

Reconstruction of parallel MRI images using high resolution image reconstruction techniques. / Reconstruction of parallel magnetic resonance imaging images using high resolution image reconstruction techniques

January 2010 (has links)
Tai, Chi Kin. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (p. 56-59). / Abstracts in English and Chinese. / Chapter 1 --- Introduction --- p.7 / Chapter 2 --- Theoretical Background --- p.9 / Chapter 2.1 --- Nuclear Magnetic Resonance --- p.9 / Chapter 2.1.1 --- Nuclear spin and macroscopic magnetization --- p.10 / Chapter 2.1.2 --- Precession and Larmor Frequency --- p.12 / Chapter 2.1.3 --- Radio-frequency excitation --- p.13 / Chapter 2.1.4 --- Radio-frequency relaxation --- p.15 / Chapter 2.1.5 --- Spin echoes --- p.17 / Chapter 2.1.6 --- Contrast mechanisms --- p.17 / Chapter 2.2 --- Magnetic Resonance Imaging --- p.20 / Chapter 2.2.1 --- MRI machine hardware --- p.20 / Chapter 2.2.2 --- Slice selection --- p.22 / Chapter 2.2.3 --- Frequency encoding --- p.23 / Chapter 2.2.4 --- Phase encoding --- p.26 / Chapter 2.2.5 --- Pulse sequences --- p.26 / Chapter 2.2.6 --- Field of view and resolution --- p.28 / Chapter 3 --- Parallel Magnetic Resonance Imaging --- p.30 / Chapter 3.1 --- Motivation --- p.30 / Chapter 3.1.1 --- Aliasing --- p.31 / Chapter 3.2 --- Coil array and coil sensitivities --- p.32 / Chapter 3.3 --- Sensitivity encoding --- p.32 / Chapter 3.3.1 --- Estimation of coil sensitivities --- p.33 / Chapter 3.3.2 --- SENSE reconstruction --- p.33 / Chapter 3.4 --- pMRI reconstruction by TV regularization --- p.35 / Chapter 3.4.1 --- Model for coil images --- p.35 / Chapter 3.4.2 --- Total variation-regularization approach --- p.36 / Chapter 4 --- Reconstruction Results --- p.39 / Chapter 4.1 --- Simulation --- p.39 / Chapter 4.1.1 --- Reconstruction quality --- p.41 / Chapter 4.1.2 --- Reconstruction results --- p.43 / Chapter 4.2 --- MRI phantom experiments --- p.44 / Chapter 4.2.1 --- Reconstruction quality --- p.48 / Chapter 4.2.2 --- Reconstruction results --- p.49 / Chapter 4.3 --- In-vivo MRI images --- p.51 / Chapter 5 --- Discussions and Conclusions --- p.54 / Bibliography --- p.56

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