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Title: Optimisation of vessel-selective magnetic resonance perfusion imaging and angiography
Author: Berry, Eleanor
ISNI:       0000 0004 6499 8076
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2016
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The diagnosis and treatment of cerebrovascular disease, such as stroke and vascular lesions in the brain, requires knowledge of the status of brain tissue and cerebral arteries. Perfusion imaging and angiography offer information on blood flow to the tissue and through the brain-feeding arteries. A variety of imaging modalities exist to assess brain haemodynamics, including measures of cerebral blood flow and other parameters, however many of these are invasive and/or involve the use of contrast agents toxic to certain patient populations. One non-invasive magnetic resonance imaging alternative for perfusion imaging and angiography, which also provides vessel specific blood flow information, is vessel-encoded pseudocontinuous arterial spin labelling (VEPCASL). VEPCASL uses the blood as an endogenous tracer and can magnetically label the blood from different arteries of interest. The combination of VEPCASL with different imaging strategies can provide a map of the vascular perfusion territories in the brain, or dynamic information on blood flow through the cerebral arteries. The work in this thesis seeks to optimise and develop the encoding process of VEPCASL and accompanying angiographic readouts. Firstly, a rapid and automated method for calculating a minimal number of signal-to-noise ratio (SNR) efficient encodings, for any number and arrangement of vessels, was developed. Its use resulted in improved SNR in perfusion territories fed by more complicated vessel arrangements in the labelling plane. The labelling efficiency of VEPCASL, and its non-vessel-selective equivalent, PCASL, is affected by the presence of magnetic field inhomogeneities in the labelling plane. Consequently, a correction for phase offsets was introduced into the calculation of the optimised encodings. These encodings enabled the recovery of SNR in perfusion territories for PCASL and VEPCASL when phase offsets were present at the labelled arteries. As current VEPCASL angiography methods are relatively slow to acquire, an accelerated readout was developed to acquire two-dimensional vessel-selective dynamic angiograms in approximately one minute. A radial k-space trajectory was found to offer the best vessel definition and SNR. Three-dimensional (3D) angiograms provide the most detailed view of the cerebral vasculature for use in diagnosis and treatment of cerebrovascular disease. A 3D radial readout was optimised to acquire vessel-selective dynamic angiograms. These angiograms offer information on the structure of the vascular tree and how it is fed by the major arteries in the neck. The techniques developed here aim to increase the clinical viability and applicability of VEPCASL perfusion imaging and angiography. It is hoped that the techniques herein could be used in patient populations to add to and improve the diagnostic information available.
Supervisor: Okell, Thomas ; Jezzard, Peter Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Magnetic resonance imaging ; Perfusion imaging ; Angiography