Evaluation of Cardiac- and Respiratory-driven Cerebrospinal Fluid Motions by Applying the S-transform to Steady-state Free Precession Phase Contrast Imaging

Purpose: To extract the status of hydrocephalus and other cerebrospinal fluid (CSF)-related diseases, a technique to characterize the cardiac-and respiratory-driven CSF motions separately under free breathing was developed. This technique is based on steady-state free precession phase contrast (SSFP-PC) imaging in combination with a Stockwell transform (S-transform). Methods: 2D SSFP-PC at 3 T was applied to measure the CSF velocity in the caudal-cranial direction within a sagittal slice at the midline (N = 3) under 6-, 10-, and 16-s respiratory cycles and free breathing. The frequency-dependent window width of the S-transform was controlled by a particular scaling factor, which then converted the CSF velocity waveform into a spectrogram. Based on the frequency bands of the cardiac pulsation and respiration, as determined by the electrocardiogram (ECG) and respirator pressure sensors, Gaussian bandpass filters were applied to the CSF spectrogram to extract the time-domain cardiac-and respiratory-driven waveforms. Results: The cardiac-driven CSF velocity component appeared in the spectrogram clearly under all respiratory conditions. The respiratory-driven velocity under the controlled respiratory cycles was observed as constant frequency signals, compared to a time-varying frequency signal under free breathing. When the widow width was optimized using the scale factor, the temporal change in the respiratory-driven CSF component was even more apparent under free breathing. Conclusion: Velocity amplitude variations and transient frequency changes of both cardiac-and respiratory-driven components were successfully characterized. These findings indicated that the proposed technique is useful for evaluating CSF motions driven by different cyclic forces.