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Optimising MRI Magnetic Susceptibility Mapping for Applications in Challenging Regions of the Body

Karsa, Anita; (2018) Optimising MRI Magnetic Susceptibility Mapping for Applications in Challenging Regions of the Body. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

Quantitative Susceptibility Mapping (QSM) is a recently developed Magnetic Resonance Imaging (MRI) technique that calculates the tissue magnetic susceptibility from MR phase images. While QSM is mostly used in brain images, it has great potential in other areas such as the head and neck where it has not yet been applied. Poorly oxygenated regions in head-and-neck tumours are expected to have a higher susceptibility due to the high concentration of paramagnetic deoxyhaemoglobin in the microvessels. Therefore, QSM could provide a non-invasive method for identifying hypoxic sites which are more resistant to radiation therapy. Therefore, the main goal of this work was to develop and optimise a QSM pipeline for the head-and-neck region. Applying the complicated processing procedure of QSM to this region is particularly challenging due to: ♦ unavoidable subject motion (e.g. swallowing), ♦ air-tissue interfaces inducing large background fields to be removed, ♦ and fatty tissue introducing an additional, chemical shift-induced phase component to the MRI signal. Moreover, as I have shown in the thesis, acquisition parameters such as image resolution and coverage of the region of interest have a substantial effect on measured susceptibilities. Therefore, tailoring the MRI acquisition is also crucial for accurate QSM in the head-and-neck region. I conducted a comprehensive optimisation of both the MRI acquisition and the QSM pipeline for head-and-neck images and addressed all the aforementioned problems. I developed and optimised a 6-minute acquisition protocol and a QSM processing pipeline. I also created a highly efficient phase unwrapping algorithm for challenging regions. Then, I showed that QSM, using the optimised protocol and pipeline, has high repeatability in the head and neck. Further, I applied this experience with a challenging region to clinical, pelvic MR images of the sacroiliac joint. I showed that bone marrow fat metaplasia has signi cantly higher susceptibility than normal bone marrow mainly due to its fat content.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Optimising MRI Magnetic Susceptibility Mapping for Applications in Challenging Regions of the Body
Event: University College London
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Copyright © The Author 2018. Original content in this thesis is licensed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) Licence (https://creativecommons.org/licenses/by/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms.
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Med Phys and Biomedical Eng
URI: https://discovery.ucl.ac.uk/id/eprint/10064348
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