Ultrasound vector Doppler techniques for three-dimensional (3-D) blood velocity measurements are currently limited by low temporal resolution and high computational cost. In this paper, an efficient 3-D high-frame-rate vector Doppler method, which estimates the displacements in the frequency domain, is proposed. The novel method extends to 3-D an approach so far proposed for two-dimensional (2-D) velocity measurements by approximating the (x, y, z) displacement of a small volume through the displacements estimated for the 2-D regions parallel to the y and x directions, respectively. The new method was tested by simulation and experiments for a 3.7 MHz, 256-element, 2-D piezoelectric sparse spiral array. Simulations were also performed for an equivalent 7 MHz Capacitive Micromachined Ultrasonic Transducer spiral array. The results indicate performance (bias ± standard deviation: 6.5 ± 8.0) comparable to the performance obtained by using a linear array for 2-D velocity measurements. These results are particularly encouraging when considering that sparse arrays were used, which involve a lower signal-to-noise ratio and worse beam characteristics with respect to full 2-D arrays.

Current 3-D Vector Flow Imaging (VFI) techniques are typically limited by either low temporal resolution and/or high computational cost. In this work, we illustrate a 3-D high frame rate VFI method, which efficiently splits the 3-D (x, y, z) displacement estimation in two separate 2-D VFI estimations operated in the frequency domain. The echo-data received after the transmission of plane waves are beamformed and high-pass filtered before being VFI processed. The new method was experimentally tested by using the ULA-OP 256 research system connected to a 3 MHz, 256-element, 2-D spiral array. Phantom experiments were conducted in steady laminar flow conditions for different probe-to-flow angles. For the tested conditions, the mean relative bias was 11.5% with a standard deviation of 10.9%. The 2-step approach applied to the 2-D VFI technique makes the new 3-D VFI method accurate and computationally efficient.