Fig 3.

Four consecutive PCMR images of the 14 images obtained during one cardiac cycle in the upper cervical spine demonstrating flow in the subarachnoid space and in cervical arteries and veins. The first image shows flow anterior and posterior to the spinal cord has a positive sign (caudad direction). The second image shows flow anterolateral to the cord remains positive whereas flow in the midline anterior to the cord has a negative sign (cephalad). The third image shows more voxels with cephalad flow and fewer with caudad flow. The fourth image shows predominantly cephalad flow with little caudad flow detected. The 2 vessels anterolateral to the subarachnoid space have caudad flow in each of the 4 images.