Baseband Delay-Multiply-and-Sum (BB-DMAS) beamforming takes advantage of the baseband spatial coherence of receiving aperture to improve image resolution and contrast. Meanwhile, the side-lobe clutter and noise level can also be effectively suppressed in BB-DMAS beamforming due to their low coherence when being detected by channels in different spatial locations. BB-DMAS scales the magnitude of channel signal by p-th root and restores the output dimensionality by p-th power after channel summation. Higher p value introduces more spatial coherence into DMAS beamforming and provides higher image resolution at the cost of background speckle quality. In this study, a computationally efficient integration of BB-DMAS with minimum-variance (MV) beamforming is developed so that the image resolution can be drastically improved with low p value (e.g. p < 2) while maintaining the speckle quality. For each image pixel, the proposed MV-DMAS only requires single MV estimation to optimize the aperture apodization for DMAS beamforming. Our simulation results show that, with p = 1.5, the -6-dB lateral width of wire reflector noticeably improves from 0.22 mm to 0.13 mm by adopting MV estimation in BB-DMAS beamforming. In MV-DMAS, the suppression of uncorrelated random noises also remains effective. Experimental results not only confirm the superior resolution in MV-DMAS beamforming but also demonstrates comparable image contrast and speckle quality to BB-DMAS counterpart. In conclusion, MV-DMAS beamforming can provide improvement in image resolution while maintaining the other image quality metrics using an efficient combination of moderate spatial coherence and MV estimation of receiving aperture apodization in ultrasonic imaging.

中文翻译：

---

用于可调节增强超声图像分辨率的计算有效的最小方差基带延迟乘法和波束成形

基带延迟乘法和求和 (BB-DMAS) 波束成形利用接收孔径的基带空间相干性来提高图像分辨率和对比度。同时，BB-DMAS波束成形中的旁瓣杂波和噪声水平由于被不同空间位置的信道检测时的相干性低，也可以得到有效抑制。BB-DMAS 通过 p 次方根缩放通道信号的幅度，并在通道求和后通过 p 次方恢复输出维数。较高的 p 值会在 DMAS 波束形成中引入更多的空间相干性，并以背景散斑质量为代价提供更高的图像分辨率。在这项研究中，开发了 BB-DMAS 与最小方差 (MV) 波束成形的计算高效集成，以便可以在低 p 值（例如 p < 2）同时保持散斑质量。对于每个图像像素，所提出的 MV-DMAS 只需要单个 MV 估计来优化 DMAS 波束成形的孔径切趾。我们的仿真结果表明，当 p = 1.5 时，通过在 BB-DMAS 波束成形中采用 MV 估计，导线反射器的 -6-dB 横向宽度从 0.22 mm 显着提高到 0.13 mm。在 MV-DMAS 中，对不相关随机噪声的抑制也仍然有效。实验结果不仅证实了 MV-DMAS 波束成形的卓越分辨率，而且还证明了与 BB-DMAS 对应的图像对比度和散斑质量相当。综上所述，