Effects Influencing Focusing in Synthetic Aperture Vector Flow Imaging
Effects Influencing Focusing in Synthetic Aperture Vector Flow Imaging
复制标题
合成孔径矢量流成像中影响聚焦的效应
DOI：
10.1109/tuffc.2007.465
复制
发表时间：
2007
期刊：
影响因子：
--
通讯作者：
J. Jensen
中科院分区：
文献类型：
--
作者：
N. Oddershede;J. Jensen
在此之前，提出了一种合成孔径矢量速度估计方法。数据通过一个点在不同方向上波束形成，在这个点上估计速度。通过寻找在该方向上发现归一化互相关峰和速度大小的方向来估计流动方向。本文研究了影响该方法聚焦的各种因素。这包括在发射的球面波相位误差的影响，运动的影响，以及在波束形成的各种插值方法的影响。利用虚拟源的概念，建立了基于幅度降和相位误差的球面波模型。该模型可用于确定虚拟源的开启角。对不同的虚拟源放置位置进行了仿真，建议在成像浅层结构时将虚拟源放置在孔径后，在成像深部结构时将虚拟源放置在孔径前。合成孔径法涉及对大量发射数据的求和。这些发射之间的运动导致不相干，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，无论在轴向运动还是横向运动下，合成孔径矢量速度估计方法的对比度和信噪比都会受到严重影响。在波束形成新数据时，采用先前矢量速度估计的补偿方法进行了实现和测试。许多流动模拟实验表明，采用这种补偿方法可以显著改善速度估计的偏差和标准差。性能的提高是以牺牲计算时间为代价的。可采用不同的插值方法对数据进行波束成形。在本文中，比较了使用各种更复杂的插值方法与使用线性插值方法的速度估计性能。当使用其他插值方法时，该方法的性能没有显着差异。
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 various 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.