Fig. 2

Example of CSF (image 1), arterial (image 2), and venous (image 3) ROIs as seen on an axial view at the mid-C2 vertebral level. Each scan is from a different volunteer. Left greyscale panels: phase contrast image showing craniocaudal velocities (greyscale). Right panels: anatomic image used to identify vessels and other structures. Image 1 structures: subarachnoid space (red). Image 2 structures: internal carotid (red and green) and vertebral arteries (white and blue). Image 3 structures: Internal jugular veins (red and green). Instantaneous flow rates (mL/min) at 40 time points throughout the cardiac cycle were determined in the veins, arteries, and CSF spaces using the ROI area and corresponding average velocity measurements as determined by the FLOW program. The software also provided stroke volumes for each vessel, defined as the net blood volume crossing the measurement plane per cardiac cycle