Three‐dimensional mapping of brain venous oxygenation using R 2 * oximetry

Purpose Cerebral venous oxygenation (Y v ) is an important biomarker for brain diseases. This study aims to develop anR 2 * ‐based MR oximetry that can measure cerebral Y v in 3D. Methods This technique separates blood signal from tissue by velocity‐encoding phase contrast and measures theR 2 *of pure blood by multi‐gradient‐echo acquisition. The bloodR 2 *was converted to Y v using anR 2 * ‐versus‐oxygenation (Y) calibration curve, which was obtained by in vitro bovine blood experiments. Reproducibility, sensitivity, validity, and resolution dependence of the technique were evaluated. Results In vitroR 2 * ‐Y calibration plot revealed a strong dependence of bloodR 2 *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%. Intrasession coefficient of variation of the measurement was 3.0%. The technique detected an average Y v increase of 10.8% as a result of hyperoxia, which was validated by global oxygenation measurement from T 2 ‐Relaxation‐Under‐Spin‐Tagging (TRUST) MRI. Two spatial resolutions, one with an isotropic voxel dimension and the other with a nonisotropic dimension, were tested for full brain coverage. Conclusions This study demonstrated the feasibility of 3D brain oxygenation mapping without using contrast agent. Magn Reson Med 79:1304–1313, 2018. © 2017 International Society for Magnetic Resonance in Medicine.