Real-Time High Frame Rate Color Flow Mapping System

Plane wave transmission (TX) can be profitably used to improve the performance of Color Flow Mapping (CFM) systems by increasing the autocorrelation ensemble length and/or the frame rate. Although high-end scanners tend to include imaging schemes using plane wave TX and parallel receive beams, high-frame-rate CFM has been so far experimentally implemented mostly through research platforms that transmit plane waves and beamform/process the received channel data off-line. In this paper, full real-time implementation of plane wave CFM with continuous-time clutter filtering and extended frame-rate/ensemble length is reported. The FPGAs and DSPs onboard the ULA-OP 256 research scanner were programmed to perform high-speed parallel beamforming and autocorrelation-based CFM processing, respectively. Different strategies were tested, in which the transmission of plane waves for CFM is either continuous or interleaved with the transmission of packets of B-Mode pulses. A 4th order Chebyshev continuous-time high-pass filter with programmable cut-off frequency was implemented and its clutter rejection performance was positively compared to that obtained when operating on packet-data. CFM frame rates up to 575 were obtained. The possibility of programming the autocorrelation ensemble length up to 64 permitted to detect flow with high sensitivity and accuracy (average relative errors down to 0.4 ± 8.4 %). In vivo HFR movies are presented, showing the dynamics of flow in the common carotid artery that highlight the presence of secondary flow components.