Bidirectional BOLD-CSF coupling using sagittal BOLD imaging with additional saturation slab for glymphatic function assessment

Motivation: Inflow-sensitized BOLD-CSF coupling analysis is corrupted by spin history effects where CSF-outflow measurements affect subsequent inflow measurements and vice versa. A method that can measure bi-directional flow and simultaneous cortical BOLD is required for accurate estimation of BOLD-CSF dynamics. Goal(s): To develop an easily implementable, fast, bi-directional alternative for BOLD-CSF coupling measurements. Approach: Using sagittal scans in combination with a saturation slab instead of axial scanning. Results: The new technique provides in- and outflow CSF-measurements in the fourth ventricle. BOLD-CSF coupling was found to be comparable between the new bi-directional sagittal and original axial method. Impact: Interest in BOLD-CSF coupling is increasing in clinical studies as a measure of brain clearance efficiency. We propose a new bi-directional sagittal approach that could give more robust BOLD-CSF coupling and later potentially quantitative bi‑directional CSF-flow extending on modelling approaches.