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Title: Advances in magnetic resonance imaging reconstruction methods incorporating prior knowledge
Author: Aitken, Andrew Peter
ISNI:       0000 0004 5917 8858
Awarding Body: King's College London
Current Institution: King's College London (University of London)
Date of Award: 2015
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In magnetic resonance (MR) imaging it is usually assumed that the acquired data represent samples of the Fourier transform of the object. However, there are many cases where this assumption is violated due to system imperfections, subject motion and deliberate undersampling in an effort to reduce scan times. This can lead to artefacts in the reconstructed images. In this thesis two emerging clinical applications of MRI are considered: hybrid PET-MR imaging and coronary MR angiography (CMRA). Factors giving rise to substantial deviations from the basic Fourier model in these cases are described and methods to reduce artefacts by incorporating additional information into the reconstruction are presented. This information is either in the form of additional measurements, or as sparsity priors. Two major limitations of current techniques for PET attenuation correction using ultrashort echo-time MRI are addressed: Artefacts due to eddy currents and prohibitively long scan times. To account for eddy currents the use of a magnetic field camera to measure the true k-space trajectories is proposed. The method is demonstrated in numerical and tissue phantoms and in vivo cranial imaging of healthy volunteers. Parallel imaging and compressed sensing are then explored to accelerate the acquisition. A method to improve motion correction for CMRA is also proposed based on a novel image navigation scheme. This method uses a golden radial trajectory, which provides both high-temporal-resolution translational and low-temporalresolution affine motion estimates from the same navigator data. The approach is demonstrated in healthy volunteers, leading to improved depiction of the coronary arteries compared to when correcting only for translational motion. Furthermore, the proposed method gives rise to a predictable and reduced scan time compared to a gated diaphragmatic navigator scan, while maintaining a high image quality. The advances in the reconstruction that are proposed in this thesis help to tackle some of the major problems with UTE-based attenuation correction for PET and with CMRA. The proposed methods help to bring these emerging applications of MRI towards routine clinical practice.
Supervisor: Prieto Vasquez, Claudia ; Schaeffter, Tobias Richard Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available