Pixel-based beamforming generates focused data by assuming that the waveforms received on a linear transducer array are composed of spherical pulses. It does not take into account the spatiotemporal spread in the data from the length of the excitation pulse or from the transfer functions of the transducer elements. As a result, these beamformers primarily have impacts on lateral, rather than axial, resolution. This paper proposes an efficient method to improve the axial resolution for pixel-based beamforming. We extend our field pattern analysis and show that the received waveforms should be passed through a Wiener filter before being used in the coherent pixel-based beamformer. This filter is designed based on signals echoed from a single scatterer at the transmit focus. The beamformer output is then combined with a coherence factor, that is adaptive to the signal-to-noise ratio, to improve the image contrast and suppress artifacts that have arisen during the filtering process. We validate the proposed method and compare it with other beamforming strategies using a series of experiments, including simulation, phantom and in vivo studies. It is shown to offer significant improvements in axial resolution and contrast over coherent pixel-based beamforming, as well as other spatial filters derived from synthetic aperture imaging. The method also demonstrates robustness to modeling errors in the experimental data. Overall, the imaging results show that the proposed approach has the potential to be of value in clinical applications.

基于像素的波束成形假设线性换能器阵列上接收到的波形由球面脉冲组成，从而生成聚焦数据。它没有考虑来自激励脉冲长度或来自换能器元件的传递函数的数据中的时空扩展。因此，这些波束形成器主要影响横向分辨率，而不是轴向分辨率。本文提出了一种有效的方法来提高基于像素的波束成形的轴向分辨率。我们扩展了我们的场模式分析，并表明在用于基于相干像素的波束形成器之前，接收到的波形应该通过维纳滤波器。该滤波器是根据从发射焦点处的单个散射体回波的信号设计的。然后将波束形成器输出与相干因子，适应信噪比，以提高图像对比度并抑制滤波过程中出现的伪影。我们验证了所提出的方法，并使用一系列实验（包括模拟、幻影和体内研究）将其与其他波束形成策略进行了比较。与基于相干像素的波束成形以及源自合成孔径成像的其他空间滤波器相比，它显示出在轴向分辨率和对比度方面的显着改进。该方法还证明了对实验数据中的建模错误的鲁棒性。总体而言，成像结果表明所提出的方法具有在临床应用中具有价值的潜力。