Synthetic aperture (SA) ultrasound imaging can obtain images with high-resolution owing to its ability to dynamically focus in both directions. The signal-to-noise ratio (SNR) of SA imaging is poor because the pulse energy using one array element is quite low. Thus, the SA method with bidirectional pixel-based focusing (SA-BiPBF) was previously proposed as a solution to this challenge. However, using the nonadaptive delay-and-sum (DAS) beamforming still limits its imaging performance. This study proposes an adaptive scaled coherence factor (AscCF) for SA-BiPBF to further boost the image quality. The AscCF exploits generalized coherence factor (GCF) to measure the signal coherence to adaptively adapt the parameters in SNR estimation rather than fixed ones. Comparisons were made with several other weighting techniques by performing simulations and experiments for performance evaluation. Results confirm that AscCF applied to SA-BiPBF offers a good image contrast while reservation of the speckle pattern. AscCF achieves maximal improvements of contrast ratio (CR) by 48.5% and 47.76 % compared with scaled coherence factor (scCF), respectively in simulation and experiment. Simultaneously, the maximum of improvements in speckle signal-to-noise ratio (sSNR) of AscCF are 11.28 % and 20.01 % upon scCF in simulation and experiment, respectively. From the in vivo result, it also appears a potential for AscCF to act in clinical situations to better detect lesion and retain speckle pattern.

合成孔径 (SA)超声成像由于能够在两个方向上动态聚焦，因此可以获得高分辨率的图像。SA 成像的信噪比 (SNR) 很差，因为使用一个阵元的脉冲能量非常低。因此，先前提出了基于双向像素聚焦的 SA 方法（SA-BiPBF）作为应对这一挑战的解决方案。然而，使用非自适应延迟求和 (DAS) 波束成形仍然限制了它的成像性能。本研究为 SA-BiPBF 提出了一种自适应缩放相干因子 (AscCF)，以进一步提高图像质量。AscCF 利用广义相干因子 (GCF) 来测量信号相干性，以自适应地调整 SNR 估计中的参数而不是固定参数。通过执行模拟和性能评估实验，与其他几种加权技术进行了比较。结果证实应用于 SA-BiPBF 的 AscCF 提供了良好的图像对比度，同时保留了散斑图案。在模拟和实验中，AscCF 与缩放相干因子 (scCF) 相比，对比度 (CR) 分别提高了 48.5% 和 47.76%。同时，AscCF 散斑信噪比 (sSNR) 的最大改进为 11.28% 和 20。在模拟和实验中，scCF 分别为 01%。来自在体内结果中，AscCF 似乎也有可能在临床情况下发挥作用，以更好地检测病变并保留散斑模式。