Investigating the effects of microstructure and magnetic susceptibility in MRI
Over the last decade, phase measurements derived from gradient echo MRI have increasingly been used as a source of quantitative information, allowing tissue composition and microstructure to be probed in vivo and opening up many new avenues of research. However, the non-local nature of phase contra...
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| Format: | Thesis (University of Nottingham only) |
| Language: | English |
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2016
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| Online Access: | https://eprints.nottingham.ac.uk/31035/ |
| _version_ | 1848794114259156992 |
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| author | Cronin, Matthew John |
| author_facet | Cronin, Matthew John |
| author_sort | Cronin, Matthew John |
| building | Nottingham Research Data Repository |
| collection | Online Access |
| description | Over the last decade, phase measurements derived from gradient echo MRI have increasingly been used as a source of quantitative information, allowing tissue composition and microstructure to be probed in vivo and opening up many new avenues of research. However, the non-local nature of phase contrast and the complexity of the underlying sources of phase variation mean that care must be taken in the interpretation and exploitation of phase information. The work described in this thesis explores the application of phase-based quantitative susceptibility measurements in vivo, and uses theory, experiment, and simulation to investigate the contribution of local structural effects to measurements of MRI signal phase.
In initial work, the use of phase imaging and quantitative susceptibility mapping (QSM) is compared in the analysis of white matter lesions in multiple sclerosis, demonstrating in vivo the dipolar distortions inherent in phase images, and the correction of such artefacts through the application of QSM, based on a thresholded k-space division method . Visual analysis of the lesions with a focus on the presence of the peripheral rings that occur in some white matter lesions allows comparison of our data with previous studies.
A theoretical description of effects of magnetic susceptibility anisotropy using a susceptibility tensor model is then presented, and its predictions tested using macroscopic phantoms composed of pyrolytic graphite sheet, a highly anisotropic and diamagnetic material. The results of these experiments confirm that the full tensor model must be used to predict the effects of structures composed of such materials on the magnetic field.
Finally, Monte Carlo simulation is used to demonstrate the effects of perturber shape and diffusion on the MRI signal phase measured from a volume containing oriented, NMR-invisible, spheroidal perturbers with constant bulk magnetic susceptibility. The rate of phase accumulation over time is shown to be highly dependent on perturber shape and diffusion, and the possible implication of these results on real MRI measurements are discussed. |
| first_indexed | 2025-11-14T19:11:03Z |
| format | Thesis (University of Nottingham only) |
| id | nottingham-31035 |
| institution | University of Nottingham Malaysia Campus |
| institution_category | Local University |
| language | English |
| last_indexed | 2025-11-14T19:11:03Z |
| publishDate | 2016 |
| recordtype | eprints |
| repository_type | Digital Repository |
| spelling | nottingham-310352025-02-28T11:45:53Z https://eprints.nottingham.ac.uk/31035/ Investigating the effects of microstructure and magnetic susceptibility in MRI Cronin, Matthew John Over the last decade, phase measurements derived from gradient echo MRI have increasingly been used as a source of quantitative information, allowing tissue composition and microstructure to be probed in vivo and opening up many new avenues of research. However, the non-local nature of phase contrast and the complexity of the underlying sources of phase variation mean that care must be taken in the interpretation and exploitation of phase information. The work described in this thesis explores the application of phase-based quantitative susceptibility measurements in vivo, and uses theory, experiment, and simulation to investigate the contribution of local structural effects to measurements of MRI signal phase. In initial work, the use of phase imaging and quantitative susceptibility mapping (QSM) is compared in the analysis of white matter lesions in multiple sclerosis, demonstrating in vivo the dipolar distortions inherent in phase images, and the correction of such artefacts through the application of QSM, based on a thresholded k-space division method . Visual analysis of the lesions with a focus on the presence of the peripheral rings that occur in some white matter lesions allows comparison of our data with previous studies. A theoretical description of effects of magnetic susceptibility anisotropy using a susceptibility tensor model is then presented, and its predictions tested using macroscopic phantoms composed of pyrolytic graphite sheet, a highly anisotropic and diamagnetic material. The results of these experiments confirm that the full tensor model must be used to predict the effects of structures composed of such materials on the magnetic field. Finally, Monte Carlo simulation is used to demonstrate the effects of perturber shape and diffusion on the MRI signal phase measured from a volume containing oriented, NMR-invisible, spheroidal perturbers with constant bulk magnetic susceptibility. The rate of phase accumulation over time is shown to be highly dependent on perturber shape and diffusion, and the possible implication of these results on real MRI measurements are discussed. 2016-03-15 Thesis (University of Nottingham only) NonPeerReviewed application/pdf en arr https://eprints.nottingham.ac.uk/31035/1/FOR%20PRINT%20-%20Investivating%20the%20effects%20of%20microstructure%20and%20magnetic%20susceptibility%20in%20MRI%20-%20M%20Cronin.pdf Cronin, Matthew John (2016) Investigating the effects of microstructure and magnetic susceptibility in MRI. PhD thesis, University of Nottingham. Magnetic Susceptibility; Microstructure; QSM; Phase; Anisotropy; Multiple Sclerosis; MRI; Iron; |
| spellingShingle | Magnetic Susceptibility; Microstructure; QSM; Phase; Anisotropy; Multiple Sclerosis; MRI; Iron; Cronin, Matthew John Investigating the effects of microstructure and magnetic susceptibility in MRI |
| title | Investigating the effects of microstructure and magnetic susceptibility in MRI |
| title_full | Investigating the effects of microstructure and magnetic susceptibility in MRI |
| title_fullStr | Investigating the effects of microstructure and magnetic susceptibility in MRI |
| title_full_unstemmed | Investigating the effects of microstructure and magnetic susceptibility in MRI |
| title_short | Investigating the effects of microstructure and magnetic susceptibility in MRI |
| title_sort | investigating the effects of microstructure and magnetic susceptibility in mri |
| topic | Magnetic Susceptibility; Microstructure; QSM; Phase; Anisotropy; Multiple Sclerosis; MRI; Iron; |
| url | https://eprints.nottingham.ac.uk/31035/ |