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首页> 外文期刊>IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control >Effects Influencing Focusing in Synthetic Aperture Vector Flow Imaging
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Effects Influencing Focusing in Synthetic Aperture Vector Flow Imaging

机译：合成孔径矢量流成像中影响聚焦的影响

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摘要

Previously, a synthetic aperture vector velocity estimation method was proposed. Data are beamformed at different directions through a point, where the velocity is estimated. The flow direction is estimated by a search for the direction where the normalized cross-correlation peaks and the velocity magnitude along this direction are found. In this paper, different effects that influence the focusing in this method are investigated. These include the effect of phase errors in the emitted spherical waves, motion effects, and the effect of various interpolation methods in beam- forming. A model based on amplitude drop and phase error for spherical waves created using the virtual source concept is derived. This model can be used to determine the opening angle of a virtual source. Simulations for different virtual source placements are made, and it is recommended that the virtual sources be placed behind the aperture when shallow structures are imaged, and when deeper-lying structures are imaged the virtual sources be placed in front of the aperture. Synthetic aperture methods involve summation of data from numerous emissions. Motion between these emissions results in incoherence and affects resolution, contrast, and the signal-to-noise ratio. The effects of motion on the synthetic aperture vector velocity estimation method are investigated, and it is shown that for both axial and lateral motion, the contrast and signal-to-noise ratio can be seriously affected. A compensation method using the previous vector velocity estimate, when new data are beamformed, is implemented and tested. It is shown from a number of flow phantom experiments that a significant improvement with respect to bias and standard deviation of the velocity estimates can be obtained by using this compensation. Increased performance is gained at the expense of computation time. Different interpolation methods can be used for beam- forming the data. In this paper, the velocity estimation performance using -n-nvarious more complex interpolation schemes are compared to that using linear interpolation. No significant difference in the performance of the method is seen when other interpolation methods are used.
机译：以前，提出了一种合成孔径矢量速度估计方法。数据在一个不同的方向通过一个点进行波束成形，估计速度。通过搜索找到归一化互相关峰和沿该方向的速度幅值的方向来估计流向。在本文中，研究了影响该方法聚焦的不同效果。这些包括发射的球面波中的相位误差的影响，运动影响以及波束形成中各种插值方法的影响。推导了基于幅度下降和相位误差的虚拟源概念创建的球形波模型。该模型可用于确定虚拟源的打开角度。对不同的虚拟源放置进行了仿真，建议在对浅结构成像时将虚拟源放置在孔的后面，在对较深的结构成像时，建议将虚拟源放置在孔的前面。合成孔径方法涉及来自多种排放物的数据求和。这些发射之间的运动会导致不连贯，并影响分辨率，对比度和信噪比。研究了运动对合成孔径矢量速度估计方法的影响，结果表明，对于轴向和横向运动，对比度和信噪比都会受到严重影响。当对新数据进行波束成形时，将实现并测试使用先前矢量速度估计的补偿方法。从许多流幻影实验中可以看出，通过使用这种补偿，可以大大提高速度估计的偏差和标准偏差。以牺牲计算时间为代价获得提高的性能。可以使用不同的插值方法对数据进行波束形成。在本文中，将使用-n-n个更复杂的插值方案的速度估计性能与使用线性插值的速度估计性能进行了比较。使用其他插值方法时，该方法的性能没有明显差异。

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