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Optimising MRI magnetic susceptibility mapping for the study of brain arteriovenous malformations

Biondetti, Emma; (2019) Optimising MRI magnetic susceptibility mapping for the study of brain arteriovenous malformations. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

Magnetic resonance imaging (MRI) magnetic susceptibility mapping (SM) enables the calculation of the magnetic susceptibility of biological tissues based on the signal phase of a gradient-recalled echo (GRE) MRI acquisition. Because deoxygenated haemoglobin is paramagnetic, SM can be used to calculate the χ of venous blood which is proportional to venous oxygen saturation (SvO2). In this thesis, I investigated the feasibility of SM for the study of brain arteriovenous malformations (AVMs). AVMs are congenital vascular anomalies characterised by arteriovenous shunting through a network of coiled and tortuous vessels. Because of this anatomy, the venous drainage of an AVM contains high-pressure mixed arterial and venous blood. I investigated whether SM could detect any resulting increased oxygenation in the draining veins. Using numerical simulations and healthy volunteer data, I focussed on optimising the acquisition and processing of GRE phase data to achieve the best possible accuracy and precision for venous SM. I showed that acquiring multi-echo versus single-echo GRE data led to more accurate and precise susceptibility, and that combining the signal from multiple echoes before applying Laplacian-based phase unwrapping or background field removal increased the susceptibility’s accuracy. Based on healthy volunteer and patient data (before and after gamma knife radiosurgery (GKR)) I investigated the feasibility of SM of brain AVMs and the information provided by venous susceptibility on AVM pathophysiology. I showed that an AVM was detectable on a susceptibility map and that the AVM draining pattern had a significantly higher SvO2 compared to healthy veins. Flowing spins in blood cause an additional susceptibility-independent component in the GRE signal phase. Because clinical multi-echo GRE protocols, including the one developed here to study brain AVMs, do not compensate for flow-induced dephasing, I investigated the effect of flow compensation on venous susceptibility and SvO2 measurements and found only a minimal effect.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Optimising MRI magnetic susceptibility mapping for the study of brain arteriovenous malformations
Event: UCL (University College London)
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Copyright © The Author 2019. 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. Access may initially be restricted at the author’s request.
UCL classification: UCL
UCL > Provost and Vice Provost Offices
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/10065508
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