Multi-line measurements of blood velocity vectors in real-time

Standard Doppler ultrasound investigations are limited to detect the axial blood velocity component, as they cannot directly estimate the flow direction. A typical approach for obtaining velocity vectors consists in combining the Doppler shifts detected by receiving the echoes from two (or more) different directions. Together with plane wave transmission, this strategy can assess the velocity data over a 2D region. Real time performance is achievable, provided that the electronics is capable of beamforming and processing the data acquired from several probe apertures in between consecutive transmissions. Recently, the ULA-OP 256 research scanner was equipped with a beamformer that, exploiting a parallel/serial process strategy, grants the calculation power for beamforming and processing multiple lines. In this work we present a vector Doppler method, based on the transmission of plane waves, which detects the velocity vectors on 8 parallel lines distributed over a 2D region 1 cm wide. The method is implemented on the ULA-OP 256 scanner and it achieves, in real-time, a refresh rate higher than 20 Hz when combined in duplex with a standard B-mode. Experiments on the carotid artery of a volunteer are reported, which show the effectiveness of the real-time implementation in detecting the complex flow patterns present in the carotid.