Cardoso J C, Ruano M G, Fish P J
School of Electronic Engineering and Computer Systems University of Wales, Bangor, Gwynedd, U.K.
IEEE Trans Biomed Eng. 1996 Dec;43(12):1176-86. doi: 10.1109/10.544341.
The spectral width of Doppler signals is used as measure of lesion-induced flow disturbance. Its estimation accuracy is compromised using the conventional short-term Fourier transform (STFT) since this method implicitly assumes signal stationarity during the signal window while the Doppler signals from arteries are markedly nonstationary. The Wigner-Ville (WVD), Choi-Williams (CWD) and Bessel distributions (BD), specifically designed for nonstationary signals, have been optimized for spectral width estimation accuracy and compared to the STFT under different signal to noise ratios using simulated Doppler signals of known time-frequency characteristics. The optimum parameter values for each method were determined as a Hanning window duration of 10 ms for the STFT, 40 ms for the WVD and CWD and 20 ms for the BD and dimensionless time-frequency smoothing constant values of five in the CWD and two in the BD. Thresholding was used to reduce the effect of cross terms and side lobes in the WVD and BD. With no added noise the WVD gave the lowest estimation error followed by the CWD. At signal-to-noise ratios (SNR's) of 10 dB and 20 dB the CWD and BD had similar errors and were markedly better than the other estimators. Overall the CWD gave the best performance.
多普勒信号的频谱宽度被用作病变引起的血流紊乱的度量指标。使用传统的短时傅里叶变换（STFT）会降低其估计精度，因为该方法隐含地假设在信号窗口期间信号是平稳的，而来自动脉的多普勒信号明显是非平稳的。专门为非平稳信号设计的维格纳 - 威利（WVD）、崔 - 威廉姆斯（CWD）和贝塞尔分布（BD），已针对频谱宽度估计精度进行了优化，并使用具有已知时频特性的模拟多普勒信号，在不同信噪比下与STFT进行了比较。确定了每种方法的最佳参数值，对于STFT为10 ms的汉宁窗持续时间，对于WVD和CWD为40 ms，对于BD为20 ms，以及对于CWD为5且对于BD为2的无量纲时频平滑常数。使用阈值处理来减少WVD和BD中交叉项和旁瓣的影响。在无附加噪声的情况下，WVD给出的估计误差最低，其次是CWD。在10 dB和20 dB的信噪比下，CWD和BD具有相似的误差，并且明显优于其他估计器。总体而言，CWD表现最佳。
