Ledoux L A, Willigers J M, Brands P J, Hoeks A P
Department of Biophysics, Maastricht University, The Netherlands.
Ultrason Imaging. 1998 Oct;20(4):223-42. doi: 10.1177/016173469802000401.
Conventional pulsed ultrasound systems are able to assess motion of scatterers in the direction of the ultrasound beam, i.e., axial motion, by determining the lag at which the maximum correlation occurs between consecutively-received radiofrequency (rf) signals. The accuracy, resolution, and processing time of this technique is improved by making use of a model for the correlation of rf signals. All previously-described correlation models only include axial motion, but it is common knowledge that lateral motion, i.e., motion in the plane perpendicular to the beam axis, reduces the correlation of rf signals in time. In the present paper, a model for the correlation of analytic rf signals in depth and time is derived and verified. It also includes, aside of some signal and transducer parameters, both axial and lateral motion. The influence of lateral motion on the correlation of (analytic) rf signals is strongly related to local phase and amplitude characteristics of the ultrasound beam. It is shown how the correlation model, making use of an ultrasound transducer with a circular beam shape, can be applied to estimate, independent of angle, the magnitude of the actual motion. Furthermore, it is shown that the model can be applied to estimate the local signal-to-noise ratio and rf bandwidth.
传统的脉冲超声系统能够通过确定连续接收的射频（rf）信号之间出现最大相关性时的延迟，来评估散射体在超声束方向上的运动，即轴向运动。通过使用射频信号相关性模型，可提高该技术的准确性、分辨率和处理时间。所有先前描述的相关性模型仅包括轴向运动，但众所周知，横向运动，即在垂直于波束轴的平面内的运动，会降低射频信号在时间上的相关性。在本文中，推导并验证了一个关于深度和时间上解析射频信号相关性的模型。除了一些信号和换能器参数外，该模型还包括轴向和横向运动。横向运动对（解析）射频信号相关性的影响与超声束的局部相位和幅度特性密切相关。展示了如何利用具有圆形波束形状的超声换能器的相关性模型，独立于角度来估计实际运动的大小。此外，还表明该模型可用于估计局部信噪比和射频带宽。
