Hoskins P R
Medical Physics and Medical Engineering Department, Royal Infirmary, Edinburgh, U.K.
Ultrasound Med Biol. 1991;17(7):703-8. doi: 10.1016/0301-5629(91)90102-3.
The effect of two noise reduction algorithms on the accuracy of estimation of the maximum frequency envelope and pulsatility index (PI) of simulated umbilical artery Doppler waveforms was investigated. The algorithms were: first, smoothing of the envelope from unfiltered Doppler spectra using a double window modified trimmed mean (DWMTM) filter and second, speckle and noise reduction of the Doppler spectrum using an image processing method. The test population consisted of waveforms were the degree of beam-vessel misalignment had been varied. The accuracy of estimation of the maximum frequency envelope and the PI was calculated by comparing each set of waveforms with the gold-standard maximum frequency envelope from the ensemble averaged waveform obtained with no misalignment. Speckle reduction gave rise to PI values that were low by approximately 0.1 (3%-4%). When there was no background noise present the improvements in envelope estimation were factors of 1.27 and 1.24, respectively, for the DWMTM method and the spectral filter, whereas the factors were 1.56 and 2.07 when background noise was present. For estimation of PI the DWMTM filter was superior. For no background noise the DWMTM filter gave a factor of 3.36 improvement whereas there was no improvement with the spectral filter. When background noise was present the factors for improvement in PI estimation were 2.39 and 4.16.
研究了两种降噪算法对模拟脐动脉多普勒波形最大频率包络和搏动指数（PI）估计准确性的影响。这两种算法分别是：第一，使用双窗口修正截尾均值（DWMTM）滤波器对未滤波的多普勒频谱包络进行平滑处理；第二，使用图像处理方法对多普勒频谱进行散斑和噪声降低处理。测试群体由波束与血管错位程度不同的波形组成。通过将每组波形与未错位情况下获得的总体平均波形的金标准最大频率包络进行比较，计算最大频率包络和PI的估计准确性。散斑减少导致PI值降低约0.1（3%-4%）。当不存在背景噪声时，DWMTM方法和频谱滤波器在包络估计方面的改进系数分别为1.27和1.24，而存在背景噪声时，系数分别为1.56和2.07。对于PI估计，DWMTM滤波器更具优势。对于无背景噪声的情况，DWMTM滤波器的改进系数为3.36，而频谱滤波器没有改进。当存在背景噪声时，PI估计的改进系数分别为2.39和4.16。
