Poree Jonathan, Goudot Guillaume, Pedreira Olivier, Laborie Emeline, Khider Lina, Mirault Tristan, Messas Emmanuel, Julia Pierre, Alsac Jean-Marc, Tanter Mickael, Pernot Mathieu
IEEE Trans Ultrason Ferroelectr Freq Control. 2021 Jun;68(6):2117-2128. doi: 10.1109/TUFFC.2021.3056932. Epub 2021 May 25.
Doppler ultrasound is the premier modality to analyze 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 (CFI)] in a wide field of view (FOV) 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 FOV and at high-frame rates but at the expense of signal-to-noise ratio (SNR). However, like conventional Doppler, ultrafast Doppler is subject to aliasing for large velocities and/or large depths. In a recent study, staggered multi-pulse repetition frequency (PRF) sequences were investigated to dealias color-Doppler images. In this work, we exploit the broadband nature of pulse-echo ultrasound and propose a dual-wavelength approach for CFI dealiasing with a constant PRF. We tested the dual-wavelength bandpass 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 four times the theoretical limit. In vivo, dealiased CFI were highly consistent with unfolded Spectral Doppler ( r=0.83 , y=1.1x+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.
在临床实践中，多普勒超声是分析血流动力学的首要方式。对于传统系统，多普勒既可以提供样本容积内血流动力学的时间分辨量化（频谱多普勒），也可以在宽视野（FOV）中提供平均多普勒速度/功率[彩色血流成像（CFI）]，但帧率有限。超快并行系统的最新发展使得在宽视野和高帧率下同时评估彩色、功率和频谱多普勒成为可能，但代价是信噪比（SNR）降低。然而，与传统多普勒一样，超快多普勒对于大速度和/或大深度会出现混叠现象。在最近的一项研究中，研究了交错多脉冲重复频率（PRF）序列以消除彩色多普勒图像的混叠。在这项工作中，我们利用脉冲回波超声的宽带特性，提出了一种用于CFI去混叠的双波长方法，其PRF恒定。我们在层流模型中对双波长带通处理进行了计算机模拟测试，并在25例人体颈动脉中进行了体内验证。计算机模拟结果表明，奈奎斯特速度可以扩展到理论极限的四倍。在体内，去混叠的CFI与展开的频谱多普勒高度一致（r = 0.83，y = 1.1x + 0.1，N = 25），并提供了一致的矢量流图像。我们的结果表明，双波长处理是一种用于高速CFI的有效方法。
