High-pass-low-pass (HP-LP) reconstruction of CINE phase-contrast MRI.

A new interpretation of CINE phase-contrast (PC) MRI is presented in which flowing blood is shown to induce separate high- and low-temporal-frequency components in the resulting image sequence. The flow velocities can then be extracted from the ratio of these two components, independently of any unknown phase offset. This interpretation leads to new insights into improving temporal resolution, eliminating noise, and reducing acquisition time in PC imaging. A specific example explored in this article uses a technique related to unaliasing by Fourier-encoding the overlaps using the temporal dimension (UNFOLD) to acquire PC velocity measurements at 54-68 time points in the cardiac cycle, all within a single breath-hold of <20 s. In experimental studies, these techniques were shown to yield improved signal-to-noise ratios (SNRs) in a flow phantom and cerebrospinal fluid (CSF) flow studies, and to resolve the formation of a flow vortex during left ventricular (LV) filling in humans.