Brands P J, Hoeks A P, Reneman R S
Department of Biophysics, Cardiovascular Research Institute Maastricht, University of Limburg, The Netherlands.
Ultrasound Med Biol. 1995;21(7):945-59. doi: 10.1016/0301-5629(95)00028-p.
Ultrasound systems are widely used to visualize in real-time internal structures and blood flow velocity distributions. The latter are estimated from the received ultrasound radio frequency (RF) signals using a mean frequency estimator, capable of estimating the temporal and spatial mean frequency within a given depth and time window (estimation window). Since ultrasound RF-signals are composed of three major signal components (reflections, scattering and noise) it is necessary to suppress the power of the reflections or reverberations (stationary echo removal) to estimate the temporal mean frequency of the signal component induced by scattering originating from red blood cells. However, the stationary echo removal filter in front of the mean frequency estimator will restrict the temporal mean frequency estimation range because the power of the signal component induced by the slowly moving blood is suppressed as well. This article describes a stationary echo removal filter, acting in the RF-domain and adaptive to the temporal mean frequency of the signal component induced by stationary or slowly moving reflections and reverberations. Furthermore, a comparison in performance of this adaptive stationary echo removal filter and several static stationary echo removal filters is presented. For direct comparison of these filter algorithms as far as the effect on the temporal mean frequency estimation range is concerned, the same signal conditions in combination with the same RF-domain mean frequency estimator were used in this comparison. It could be demonstrated that the adaptive echo removal filter, in combination with the RF-domain mean frequency estimator used, exhibits the best performance.
超声系统被广泛用于实时可视化内部结构和血流速度分布。后者是使用平均频率估计器从接收到的超声射频（RF）信号中估计出来的，该估计器能够在给定深度和时间窗口（估计窗口）内估计时间和空间平均频率。由于超声RF信号由三个主要信号成分（反射、散射和噪声）组成，因此有必要抑制反射或混响的功率（去除静态回波），以估计由红细胞散射引起的信号成分的时间平均频率。然而，平均频率估计器之前的静态回波去除滤波器会限制时间平均频率估计范围，因为缓慢移动的血液引起的信号成分的功率也会被抑制。本文描述了一种在RF域中起作用的静态回波去除滤波器，它能适应由静态或缓慢移动的反射和混响引起的信号成分的时间平均频率。此外，还对这种自适应静态回波去除滤波器和几种静态静态回波去除滤波器的性能进行了比较。为了就对时间平均频率估计范围的影响而言直接比较这些滤波算法，在该比较中使用了相同的信号条件并结合相同的RF域平均频率估计器。结果表明，与所使用的RF域平均频率估计器相结合的自适应回波去除滤波器表现出最佳性能。
