Hoskins P R, Loupas T, McDicken W N
Department of Medical Physics and Medical Engineering, Royal Infirmary of Edinburgh, UK.
Ultrasound Med Biol. 1991;17(1):7-21. doi: 10.1016/0301-5629(91)90004-g.
The effect of three physical parameters on the accuracy of estimation of the maximum frequency envelope and pulsatility index (PI) of simulated umbilical artery Doppler waveforms was investigated. The physical parameters were beam-vessel angle, the offset between the beam axis and vessel axis, and the thickness of overlying attenuating material. Waveforms were acquired using a physiological flow phantom. The maximum frequency envelope was calculated using a threshold maximum frequency follower which was adaptive to the level of background noise. A gold standard maximum frequency envelope was obtained from the ensemble averaged waveform when there was alignment of beam and vessel axis, a 50 degrees beam-vessel angle and 2 cm of attenuating material. Indices of bias, variability and accuracy of estimation of the maximum frequency envelope and PI were calculated by comparing subsequent maximum frequency envelopes with the gold standard maximum frequency envelope. Both the maximum frequency envelope and PI were estimated to a similar degree of accuracy over a wide range of physical conditions. In this study, the error in PI was less than 0.15 for beam-vessel angles less than 80 degrees, for beam-vessel axis offset distances less than 7.5 mm, at a transducer-vessel distance of 5 cm, and for attenuator thicknesses less than 4.5 cm. The percentage root-mean square error for estimation of the maximum frequency envelope was approximately 10% or less for beam-vessel angles less than 75 degrees, for beam-vessel axis offset distances less than 7.5 mm, and for attenuator thicknesses less than 4 cm.
研究了三个物理参数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。这些物理参数为声束-血管角度、声束轴与血管轴之间的偏移以及覆盖的衰减材料厚度。使用生理血流模型采集波形。使用自适应于背景噪声水平的阈值最大频率跟踪器计算最大频率包络。当声束与血管轴对齐、声束-血管角度为50度且衰减材料厚度为2 cm时，从总体平均波形中获得金标准最大频率包络。通过将后续的最大频率包络与金标准最大频率包络进行比较，计算最大频率包络和PI估计的偏差、变异性和准确性指标。在广泛的物理条件范围内，最大频率包络和PI的估计精度相似。在本研究中，当声束-血管角度小于80度、声束-血管轴偏移距离小于7.5 mm、换能器-血管距离为5 cm且衰减器厚度小于4.5 cm时，PI的误差小于0.15。当声束-血管角度小于75度、声束-血管轴偏移距离小于7.5 mm且衰减器厚度小于4 cm时，最大频率包络估计的均方根误差百分比约为10%或更低。
