201. Global intravascular and local hyperoxia contrast phase-based blood oxygenation measurements
- Author
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Paula L. Croal, Susan T. Francis, Samuel Wharton, Richard Bowtell, Penny A. Gowland, and Ian D. Driver
- Subjects
Adult ,Male ,Pathology ,medicine.medical_specialty ,Large vein ,Haemodynamic response ,Oxygen saturation ,Cognitive Neuroscience ,Hyperoxia ,Article ,MR susceptometry ,Young Adult ,Image Processing, Computer-Assisted ,Humans ,Medicine ,business.industry ,Brain ,Venous oxygenation ,Magnetic Resonance Imaging ,Oxygen ,Neurology ,Oxygen extraction fraction (OEF) ,Cerebrovascular Circulation ,Phase imaging ,Blood oxygenation ,Female ,Mr images ,medicine.symptom ,business ,MRI ,Superior sagittal sinus ,Oxygen extraction ,Biomedical engineering - Abstract
The measurement of venous cerebral blood oxygenation (Yv) has potential applications in the study of patient groups where oxygen extraction and/or metabolism are compromised. It is also useful for fMRI studies to assess the stimulus-induced changes in Yv, particularly since basal Yv partially accounts for inter-subject variation in the haemodynamic response to a stimulus. A range of MRI-based methods of measuring Yv have been developed recently. Here, we use a method based on the change in phase in the MR image arising from the field perturbation caused by deoxygenated haemoglobin in veins. We build on the existing phase based approach (Method I), where Yv is measured in a large vein (such as the superior sagittal sinus) based on the field shift inside the vein with assumptions as to the vein's shape and orientation. We demonstrate two novel modifications which address limitations of this method. The first modification (Method II), maps the actual form of the vein, rather than assume a given shape and orientation. The second modification (Method III) uses the intra and perivascular phase change in response to a known change in Yv on hyperoxia to measure normoxic Yv in smaller veins. Method III can be applied to veins whose shape, size and orientation are not accurately known, thus allowing more localised measures of venous oxygenation. Results demonstrate that the use of an overly fine spatial filter caused an overestimation in Yv for Method I, whilst the measurement of Yv using Method II was less sensitive to this bias, giving Yv = 0.62 ± 0.03. Method III was applied to mapping of Yv in local veins across the brain, yielding a distribution of values with a mode of Yv = 0.661 ± 0.008., Highlights • We propose two modifications to MRI phase-based blood oxygenation measurements. • A forward field calculation is used to relax the infinite cylinder approximation. • Hyperoxia-based method overcomes vessel orientation and partial volume limitations. • Local blood oxygenation measurements in small veins, showing regional heterogeneity
- Published
- 2014