De-aliasing High-Frame-Rate Color Doppler using Dual-wavelength processing.

Doppler ultrasound is the premier modality to analyse blood flow dynamics in clinical practice. With conventional systems, Doppler can either provide a time-resolved quantification of the flow dynamics in sample volumes (Spectral Doppler) or an average Doppler velocity/power (Color Flow Imaging) in a wide field of view but with a limited frame rate. The recent development of ultrafast parallel systems made it possible to evaluate simultaneously Color, Power and Spectral Doppler in a wide field of view and at high - frame rates but at the expense of SNR. However, like conventional Doppler, Ultrafast Doppler is subject to aliasing for large velocities and/or large depths. In a recent study, staggered multi-PRF sequences were investigated to de-alias color-Doppler images. In this work, we exploit the broadband nature of pulse-echo ultrasound and propose a dual-wavelength approach for CFI de-aliasing with a constant PRF. We tested the dual-wavelength band-pass processing, in silico in laminar flow phantom and validated it in-vivo in human carotid arteries (n=25). The in silico results showed that the Nyquist velocity could be extended up to 4 times the theoretical limit. In-vivo, de-aliased CFI were highly consistent with unfolded Spectral Doppler (r2 = 0.83, y = 1.1 x + 0.1, N = 25) and provided consistent vector flow images. Our results demonstrate that dual-wavelength processing is an efficient method for high-velocity CFI.