High pulse repetition frequency vector Doppler velocity measurements

Doppler ultrasound methods are extensively used for non-invasively measuring flow velocity in blood vessels. One of the main challenges that still need to be faced is achieving angle independent estimates, especially in presence of high speed flows. A dual beam vector Doppler method was introduced so far, in which one beam is devoted to estimate the flow direction, and the second one to perform velocity measurements with known Doppler angle. Since two consecutive transmission and reception events are needed for the two beams, the effective Doppler pulse repetition frequency is halved, thus facilitating the onset of aliasing when fast flow is investigated. In this work, the problem is overcome by using, on a linear array probe, one subaperture in transmission and two sub-apertures in reception. The new approach was implemented and tested in real-time on the ULA-OP 256 open platform, taking advantage of its parallel beamforming capabilities. In-vitro experiments confirm the fair repeatability performance of the method in angle independent measurements, while the in-vivo test shows that the assessment of peak velocities higher than 2 m/s is feasible, making the method suitable for the investigation of stenotic vessels.