Fourier analysis of cerebrospinal fluid flow in cerebral aqueduct

An interleaved pseudocinematographic fast low-angle shot (FLASH) sequence with additional pulsed gradients for flow encoding was used in order to quantify cerebrospinal fluid (CSF) flow velocities and production. Flow-dependent phase information was obtained by subtraction of two differently encoded phase images and was converted to flow velocity with a calibration curve that had a slope of 1.10 degrees/mm/sec. The velocity-versus-time function was Fourier transformed, and a continuous curve was fitted to the measured data with harmonics used up to the third order. For a CSF phantom with slowly pulsating flow but with no net flow, the Fourier analysis showed that the zeroth harmonic (the offset) was negligible, indicating that the in- and outflow of the phantom were equal. In vivo, in- and outflow through the cerebral aqueduct of a healthy volunteer was seen to be - 54 and + 66 mm3 per heart cycle, giving a production of 12 mm3 per heart cycle or approximately 1.1 L/d. The proposed method seems promising as a tool for quantification of CSF flow rates and CSF production volumes