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Caitlin O'Brien


DPhil Student

The current focus of my research is to devise a method for measuring quantitative localized oxygen extraction fraction in brain using MRI methods.

Oxygen extraction fraction (OEF) is a measure of the fraction of oxygenated haemoglobin in the venous vasculature relative to the arterial vasculature. In cerebrovascular disease, such as stroke, the OEF can become abnormal. In particular, in ischaemic stroke the tissue surrounding the blood clot is expected to have elevated OEF, as a result of compromised blood flow. Identification of this tissue is important in assessing patient treatment and outcome and is therefore a theraputic target in the clinic. 

There exists a calibrated relationship between blood oxygen concentration, and the MR relaxation time T2. My sequence, Selective Localised T2-Relaxation-Under-Spin-Tagging (SL-TRUST), therefore aims to measure the relaxation time T2 of venous blood originating from a large tissue voxel in the brain. This, combined with a measure of venous blood hematocrit, allows the venous oxygenation to be quantified, and therefore the cerebral tissue OEF can be calculated.