Ledoux L A, Willigers J M, Brands P J, Hoeks A P
Department of Biophysics, Cardiovascular Research Institute Maastricht, Maastricht University, The Netherlands.
Ultrason Imaging. 1999 Jul;21(3):216-40. doi: 10.1177/016173469902100305.
In medicine, pulsed ultrasound is a widespread noninvasive technique that measures motion in the direction of the ultrasound beam, i.e., axial motion. The magnitude of the actual motion can be determined only if the angle between the ultrasound beam and the direction of motion (transducer-to-motion angle) is known. For blood flow measurements, current pulsed ultrasound systems assume this angle to be equal to the angle between the ultrasound beam and the longitudinal direction of the vessel, as can be estimated from a two-dimensional brightness-mode (B-mode) image that is obtained prior to the blood flow measurement. For tissue motion measurements, current pulsed ultrasound systems are mostly unable to determine the transducer-to-motion angle. Recently, a model has been derived for the correlation of(analytic) radiofrequency (rf) signals, assessed with a circular-shaped ultrasound transducer along the same line of observation. In the present paper, this model is used to derive estimators, requiring only the calculation of a few correlation coefficients, for the motion components (axial, lateral and actual) and for some of the signal parameters (center frequency, bandwidth and signal-to-noise ratio) of the assessed rf signals. The transducer-to-motion angle can be derived from the estimated motion components. For the evaluation of the estimators, rf signals were acquired with a motion-controlled experimental arrangement. The results of the evaluation study show that the transducer-to-motion angle can be estimated with a mean standard deviation of less than 2 degrees.
在医学中，脉冲超声是一种广泛应用的非侵入性技术，用于测量沿超声束方向的运动，即轴向运动。只有当超声束与运动方向之间的角度（换能器与运动角度）已知时，才能确定实际运动的大小。对于血流测量，当前的脉冲超声系统假定这个角度等于超声束与血管纵向方向之间的角度，这可以从血流测量之前获得的二维亮度模式（B模式）图像中估计出来。对于组织运动测量，当前的脉冲超声系统大多无法确定换能器与运动角度。最近，已经推导出一个模型，用于（解析）射频（rf）信号的相关性，该信号是用圆形超声换能器沿同一条观测线进行评估的。在本文中，该模型用于推导估计器，该估计器仅需要计算几个相关系数，用于评估的rf信号的运动分量（轴向、横向和实际）以及一些信号参数（中心频率、带宽和信噪比）。换能器与运动角度可以从估计的运动分量中推导出来。为了评估这些估计器，使用运动控制的实验装置采集了rf信号。评估研究结果表明，换能器与运动角度的估计平均标准差小于2度。
