Tsou Jean K, Liu Jie, Insana Michael F
Department of Biomedical Engineering, University of California, Davis, CA 95616, USA.
IEEE Trans Ultrason Ferroelectr Freq Control. 2006 Apr;53(4):724-34.
Wall shear rate (WSR) is the derivative of blood velocity with respect to vessel radius at the endothelial cell (EC) surface. The product of WSR and blood viscosity is the wall shear stress (WSS) that has been identified as an important factor for atherosclerosis development. High echo signal-to-noise ratio (eSNR) and high spatial resolution are crucial for minimizing the errors in WSR estimates. By transmitting coded pulses with time-bandwidth product greater than one, high eSNR from weak blood scatter can be achieved without increasing instantaneous power or sacrificing spatial resolution. This paper summarizes a series of measurements in a straight tube (5-mm diameter), constant velocity flow phantom using a 10 MHz transducer (60% bandwidth, f/1.5) imaged with a 72 degrees Doppler angle, 125 MHz sampling frequency and 1 kHz pulse repetition frequency. Measurements were made using a frequency-modulated (FM) code, phase-modulated (PM) codes, and uncoded broadband and narrow band pulse transmissions. Both simulation and experimental results show that coded-pulse excitation increases accuracy and precision in WSR estimation for laminar flow over a broad range of peak velocity values when compared to standard pulsing techniques in noise-limited conditions (eSNR < 30 dB). The code sequence and its length are selected to balance range lobe suppression with eSNR and echo coherence enhancements to minimize WSR errors. In our study, the combination of an eight bit Optimal coded pulse with a Wiener compression filter yielded the highest WSR estimation performance.
壁面剪切速率（WSR）是内皮细胞（EC）表面处血流速度相对于血管半径的导数。WSR与血液粘度的乘积是壁面剪切应力（WSS），它已被确定为动脉粥样硬化发展的一个重要因素。高回声信噪比（eSNR）和高空间分辨率对于最小化WSR估计中的误差至关重要。通过发射时间带宽积大于1的编码脉冲，可以在不增加瞬时功率或牺牲空间分辨率的情况下，从微弱的血液散射中获得高eSNR。本文总结了在一个直径5毫米的直管、恒速流动体模中进行的一系列测量，使用一个10兆赫兹的换能器（60%带宽，f/1.5），以72度的多普勒角、125兆赫兹的采样频率和1千赫兹的脉冲重复频率进行成像。测量使用了调频（FM）编码、调相（PM）编码以及未编码的宽带和窄带脉冲传输。模拟和实验结果均表明，与噪声受限条件（eSNR < 30 dB）下的标准脉冲技术相比，编码脉冲激励在较宽的峰值速度值范围内提高了层流WSR估计的准确性和精度。选择编码序列及其长度，以平衡距离旁瓣抑制与eSNR和回波相干增强，从而最小化WSR误差。在我们的研究中，八位最优编码脉冲与维纳压缩滤波器的组合产生了最高的WSR估计性能。
