Figure 13

Flow in the cerebral aqueduct from cine phase contrast MRI in a healthy control. A typical MRI flow study, using the phase contrast technique, consists of the magnitude (a, anatomical) and phase (b, flow) image. In this example, cine images were taken as a function of the cardiac cycle by gating the image acquisition to a peripheral pulse signal. The image on the right depicts flow velocities during one phase of the cardiac cycle with caudal CSF flow (the bright dot in center of the image shows caudal flow in the aqueduct during this phase of the cycle). By summing over all pixels in the aqueduct, a net flow waveform is obtained (c). Stroke volume in this instance was 25.7 μl.