Vessel-specific quantification of blood oxygenation with T ₂-relaxation-under-phase-contrast MRI

Purpose Measurement of venous oxygenation (Y_v) is a critical step toward quantitative assessment of brain oxygen metabolism, a key index in many brain disorders. The present study aims to develop a noninvasive, rapid, and reproducible method to measure Y_v in a vessel-specific manner. Theory The method, T₂-Relaxation-Under-Phase-Contrast MRI, utilizes complex subtraction of phase-contrast to isolate pure blood signal, applies nonslice-selective T₂-preparation to measure T₂, and converts T₂ to oxygenation using a calibration plot. Methods Following feasibility demonstration, several technical aspects were examined, including validation with an established global Y_v technique, test-retest reproducibility, sensitivity to detect oxygenation changes due to hypoxia and caffeine challenges, applicability of echo-planar-imaging (EPI) acquisition to shorten scan duration, and ability to study veins with a caliber of 1-2 mm. Results T₂-Relaxation-Under-Phase-Contrast was able to simultaneously measure Y_v in all major veins in the brain, including sagittal sinus, straight sinus, great vein, and internal cerebral vein. T ₂-Relaxation-Under-Phase-Contrast results showed an excellent agreement with the reference technique, high sensitivity to oxygenation changes, and test-retest variability of 3.5 ± 1.0%. The use of segmented-EPI was able to reduce the scan duration to 1.5 minutes. It was also feasible to study pial veins and deep veins. Conclusion T₂-Relaxation-Under-Phase- Contrast MRI is a promising technique for vessel-specific oxygenation measurement.