Evans J M, Beard J D, Skidmore R, Horrocks M
Department of Medical Physics, Bristol Royal Infirmary, England.
Clin Phys Physiol Meas. 1987 Nov;8(4):309-15. doi: 10.1088/0143-0815/8/4/003.
Ultrasonic Doppler-shifted signals from blood can be displayed in various forms using either analogue or digital processing techniques. One of the most commonly extracted parameters from the Doppler spectrum is the mean frequency envelope. This waveform can be used for the interpretation of physiological changes within man and can also be used for the estimation of volume flow rate within a vessel. This paper describes a practical implementation of an analogue, instantaneous mean frequency estimator and its use in the measurement of blood flow volume. The circuit is linear to within two per cent and operates over a frequency range of 200 Hz to 10 kHz. It can extract a velocity-time envelope from a Doppler signal within noise and performs well in a clinical environment. It is relatively inexpensive compared with digital signal processing techniques and requires minimal setting up. Simple connection to a Doppler velocimeter using phase quadrature demodulation will produce a directional output.
来自血液的超声多普勒频移信号可通过模拟或数字处理技术以多种形式显示。从多普勒频谱中最常提取的参数之一是平均频率包络。该波形可用于解释人体内部的生理变化，也可用于估计血管内的体积流量。本文描述了一种模拟瞬时平均频率估计器的实际实现及其在血流量测量中的应用。该电路的线性度在百分之二以内，工作频率范围为200赫兹至10千赫。它可以从噪声中的多普勒信号中提取速度-时间包络，并且在临床环境中表现良好。与数字信号处理技术相比，它相对便宜，并且设置要求最低。使用相位正交解调简单连接到多普勒测速仪将产生定向输出。
