Tortoli P, Thompson R S, Berti P, Guidi F
Dept. of Electron. Eng., Florence Univ.
IEEE Trans Ultrason Ferroelectr Freq Control. 1999;46(6):1591-6. doi: 10.1109/58.808885.
The use of a multigate profiling system with steady laminar flow in plastic tubes revealed spectral artifacts not previously described. In particular, a double or split profile was often observed. In this paper, these artifacts are related to the dual mode ultrasound propagation in the plastic tube. The propagation speeds and, therefore, refraction angles and propagation paths are different for the longitudinal and the shear wave. The power transmission can be extraordinarily sensitive to small variations in the angle of incidence, and this may combine with the existence of a range of angles of incidence within any focused ultrasound beam to produce spectral distortions. The plastic tube is thus shown equivalent to a selective filter, which diminishes some frequency components in the Doppler spectrum relative to others. The spectral artifacts are explained in terms of the relative power transmitted by each mode, and the degree of beam defocusing experienced by each. Spectral distortions persist even when the beam-to-flow orientation is well away from the critical angle. The results of this study show that it is feasible to understand the acoustic transmission behavior of a flow phantom, based on a knowledge of the material properties, and to demonstrate the usefulness of doing so.
在塑料管中使用具有稳定层流的多门控分析系统揭示了以前未描述过的频谱伪像。特别是，经常观察到双峰或分裂谱线。在本文中，这些伪像与塑料管道中的双模式超声传播有关。纵向波和剪切波的传播速度不同，因此折射角和传播路径也不同。功率传输对入射角的微小变化可能异常敏感，这可能与任何聚焦超声束内存在一系列入射角相结合，从而产生频谱失真。因此，塑料管相当于一个选择性滤波器，它会使多普勒频谱中的某些频率成分相对于其他成分减弱。频谱伪像根据每种模式传输的相对功率以及每种模式所经历的波束散焦程度来解释。即使波束与血流的方向远离临界角，频谱失真仍然存在。这项研究的结果表明，基于对材料特性的了解来理解流动模型的声学传输行为并证明这样做的有用性是可行的。
