StaBle: Staggered PRF With DouBle Transmission for Increasing the Velocity Limit of High-Frame-Rate Vector Doppler Imaging

Abstract

Vector Doppler Imaging (VDI) addresses the limitations of traditional Doppler imaging by measuring blood flow in axial and lateral directions but will produce incorrect results if aliasing is present. Aliasing becomes more likely when using high transmit frequencies such as in small animal cardiac applications. The use of multiple transmit angles decreases the Nyquist limit, which further increases the likelihood of aliasing. A new transmission scheme, termed StaBle, is proposed to increase the Nyquist limit of conventional sequential angle VDI by multiple fold. StaBle combines the velocity limit extension of staggered multiple pulse repetition frequency (PRF) with a double transmission scheme. With three transmit angles and two PRFs, StaBle was able to achieve a 6-12 times higher velocity limit compared to sequential angle VDI. Simulation and phantom spinning disk experiments were conducted to evaluate StaBle’s performance. The simulation results showed a normalized root-mean-squared error of less than 5% compared to an ideal vector field in both axial and lateral directions. Phantom results showed a 9-fold improvement in detecting peak axial velocity over sequential three angle VDI. The ability of StaBle to obtain an unaliased vector field in vivo was demonstrated by imaging a mouse left ventricle where the Doppler signal was corrupted by aliasing artifacts using just a double transmit scheme. The resolved estimated vector velocity showed consistent beat-to-beat variation in velocity, confirming StaBle’s robustness under realistic conditions and its potential for use in investigative studies.