Magnetic Resonance Imaging of Cerebral Venous Oxygenation
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Cerebral venous oxygenation (Yᵥ) is an important biomarker for brain diseases. My dissertation consisted of two studies. The first study aims to investigate the regional Yᵥ in hypertension. Hypertension is known to cause cerebral hypoperfusion and cortical atrophy but its impact on Yᵥ is not yet clear. A 2D venous oxygenation mapping technique, TRUPC was applied to an elderly cohort from Dallas Heart Study. The Yᵥ in internal cerebral veins (ICV), anterior and posterior superior sagittal sinus (SSS) and anatomical data was obtained. It was found lower relative venous oxygenation in the ICV and anterior SSS are associated with high systolic pressure. Such trend is also observed in hypertensive group alone. Moreover, the volume reduction in hippocampus and thalamus is correlated with decreased regional Yᵥ. The findings presented are consistent with previous literature on the targeted hypofusion and volume reduction in these regions. Imaging marker Yᵥ reported here may prove valuable in the understanding of hypoxia effect, hypoperfusion and cortical volume reduction caused by hypertension. The second study aims to develop an R2*-based MR oximetry that can measure cerebral Yᵥ in 3D. This technique separates blood signal from tissue by velocity-encoding phase contrast and measures the R2* of pure blood by multi-gradient-echo acquisition. The blood R2* was converted to Yᵥ using an R2*-vs-oxygenation (Y) calibration curve, which was obtained by in vitro bovine blood experiments. Reproducibility, sensitivity, validity, and resolution dependence of the technique were evaluated. In vitro R2*-Y calibration plot revealed a strong dependence of blood R2* on oxygenation, with additional dependence on hematocrit. In vivo results demonstrated that the technique can provide a 3D venous oxygenation map that depicts both large sinuses and smaller cortical veins, with venous oxygenation ranging from 57% to 72%. Intra-session coefficient-of-variation of the measurement was 3.0%. The technique detected an average Yᵥ increase of 10.8% due to hyperoxia, which was validated by global oxygenation measurement from TRUST. Two spatial resolutions, one with an isotropic voxel dimension and the other with a non-isotropic dimension, were tested for full brain coverage. This study demonstrated the feasibility of 3D brain oxygenation mapping without using contrast agent.