Correction and optimization of a T2-based approach to map blood oxygenation in small cerebral veins

Purpose Cerebral venous blood oxygenation (Y_v) is an important biomarker in brain physiology and function. The present study proposes a procedure to provide a quantitative map of the brain's intravascular Y_v. Theory and Methods The method is based on a pulse sequence, T₂-Relaxation-Under-Phase-Contrast (TRU-PC) MRI, with postprocessing approaches to correct eddy-current effects. A complete scan protocol consists of four TRU-PC scans sensitized to large and small vessels with anterior-posterior and foot-head flow-encoding directions, and the data are analyzed conjunctively. Eddy-current correction was performed by fitting the tissue phase to a hyperplane, and then subtracting the eddy-current phase from the measured vessel phase. The reproducibility of the Y_v-maps was examined in five participants. Sensitivity of the Y_v map to a caffeine challenge was studied in another five participants. Results Removal of eddy-current induced artifact allowed for the correction of T₂ measurements, as demonstrated in vivo and with simulation. A Y_v-map depicting all vessels in the slice can be obtained with the proposed protocol. Test-retest variability of the Y_v-map was 3.7 ± 1.2%. Y_v reduction can be reliably detected (P < 0.001) following the caffeine ingestion. Conclusion With the proposed TRU-PC protocol and eddy-current correction procedure, an accurate, vessel-specific Y_v map of the human brain can be obtained.