Hoeks A P, Arts T G, Brands P J, Reneman R S
Department of Biophysics, University of Limburg, Maastricht, The Netherlands.
Ultrasound Med Biol. 1993;19(9):727-40. doi: 10.1016/0301-5629(93)90090-b.
In pulsed Doppler systems the received RF (radio frequency) signal is multiplied by a quadrature reference signal and subsequently averaged over a short depth range to obtain a sample of the complex Doppler signal. The mean frequency of the sampled Doppler signal, obtained with the autocorrelation function, reflects the mean velocity of the scatterers moving through the sample volume. An alternative is to evaluate the two-dimensional cross correlation function of a short segment of the RF signals over subsequent lines, giving the mean velocity of the scatterers. Both methods of velocity estimation were applied to computer-generated RF signals with varying RF bandwidth, signal-to-noise ratio, and mean and width of the imposed velocity distribution. The length of the RF signal segment and the number of lines for velocity estimation (package length) affects the accuracy of the velocity estimate. It can be concluded that the cross correlation technique behaves superiorly especially for a low velocity dispersion. Furthermore, the standard deviation of the velocity estimate decreases for an increasing sample volume length and package length, while the performance of the conventional Doppler technique is rather independent of the length of the sample volume. The difference between both techniques decreases for a greater package length or for signals simulating a wide velocity distribution.
在脉冲多普勒系统中，接收到的射频（RF）信号与一个正交参考信号相乘，随后在一个短深度范围内进行平均，以获得复多普勒信号的一个样本。通过自相关函数获得的采样多普勒信号的平均频率，反映了穿过采样体积的散射体的平均速度。另一种方法是评估后续线上RF信号短段的二维互相关函数，从而得出散射体的平均速度。两种速度估计方法都应用于具有不同RF带宽、信噪比以及所施加速度分布的均值和宽度的计算机生成的RF信号。RF信号段的长度和用于速度估计的线数（包长度）会影响速度估计的准确性。可以得出结论，互相关技术表现更优，尤其是对于低速离散情况。此外，随着采样体积长度和包长度的增加，速度估计的标准差会减小，而传统多普勒技术的性能与采样体积的长度相当独立。对于更大的包长度或模拟宽速度分布的信号，两种技术之间的差异会减小。
