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Title: Measurement of localized oxygen extraction fraction in brain using magnetic resonance imaging
Author: O'Brien, Caitlin Fern
ISNI:       0000 0004 8507 8658
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2020
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Magnetic resonance imaging (MRI) is a non-invasive medical imaging technique which, thanks to the variety of both structural and functional information it provides, is increasingly used throughout the world for clinical diagnosis. Due to the different magnetic properties of haemoglobin when it is bound to oxygen, MRI is sensitive to the oxygen saturation levels of the blood, however, accurate measurement of this property remains challenging in the brain. Specifically, there does not yet exist a robust MR method for quantifying regional differences in brain tissue oxygenation, which can provide important diagnostic information in cases where oxygen delivery to a specific region of the brain may be impaired, e.g. in stroke. In this thesis a new method for measuring the oxygen extraction fraction of tissue in the brain on a regional level is presented. The technique is called Selective Localized T2-Relaxation-Under-Spin- Tagging, or SL-TRUST and measures the oxygen saturation of outflowing venous blood in the superior sagittal sinus. Using SL-TRUST venous oxygen saturation measurements are achieved in individual brain hemispheres and in a smaller tissue region, approximately 70x70x80 mm3, above the middle cerebral artery. Comparison of two contralateral regions can be achieved in a scan time of less than 5 minutes. The robustness of SL-TRUST is assessed in healthy volunteers in a reproducibility study and the coefficients of variation for regional measurements found to be comparable to those of global measurements. SL-TRUST is developed further as a method of mapping the oxygenation of venous blood from across the whole brain using phase encoding methods. Low resolution T2 maps in healthy volunteers are obtained as proof-of-concept of this method.
Supervisor: Jezzard, Peter ; Okell, Thomas Sponsor: Engineering and Physical Sciences Research Council ; Medical Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Magnetic resonance imaging