Real-time staggered PRF for vector Doppler blood velocity assessment

Vector Doppler techniques are ready to substitute the standard Doppler methods currently employed in clinical blood velocity investigations. However, like in classic Pulse-Wave modes, the maximum detectable velocity is related to the Pulse Repetition Frequency (PRF), which is limited by the maximum depth and/or by hardware constraints. Unfortunately, the blood velocity, e.g. in stenotic vessels, can easily peak above 1.5 m/s, which often results in aliased and unreliable measurements. Staggered PRF is a technique that, by correlating the Doppler shifts detected at different PRFs, can recover the correct velocity even when it is beyond the Nyquist limit. In this work, we applied staggered PRF to Multi Line Vector Doppler (MLVD), a 2D imaging method that, exploiting plane waves, detects velocity vectors on a 2D region composed of 8 lines placed perpendicular to a linear array probe. Real-time MLVD with staggered PRF was implemented in the ULA-OP 256 research scanner. Tests in a flow-rig show the MLVD capable of recovering the correct peak velocity up to 2.3 times the Nyquist limit.