Department of Biomedical Engineering, Hefei University of Technology, Hefei, 230009, China.
Department of Ultrasound, The First Affiliated Hospital of Anhui Medical University, Hefei, 230022, China.
Ultrasonics. 2021 Aug;115:106417. doi: 10.1016/j.ultras.2021.106417. Epub 2021 Mar 13.
Synthetic aperture (SA) imaging can provide a uniform lateral resolution but an insufficient signal-to-noise ratio (SNR). SA method with bidirectional pixel-based focusing (SA-BiPBF) has the ability to obtain a higher quality image than conventional SA imaging. In this paper, an enhanced SA-BiPBF named full aperture received far-focused pixel-based (FrFPB) is firstly proposed to obtain a high resolution image. An adjustable zero-cross factor scaled Wiener postfilter (AZFsW) is then implemented in FrFPB for improving contrast ratio (CR). The adjustable zero-cross factor is calculated using the polarity of echo signals sequence with an adjustable coefficient σ to estimate the signal coherence, and it is combined with Wiener postfilter to obtain a good capability of noise reduction and background speckle pattern preservation. Simulation and experiments have been conducted to evaluate the imaging performance of the proposed methods. Results show that FrFPB can obviously improve the resolution in comparison with SA-BiPBF, and contrast-to-noise ratio (CNR) and speckle signal-to-noise ratio (sSNR) are retained. In addition, AZFsW can achieve a much higher CR than SA-BiPBF. When σ is 0.6, the CR improvement is 96.7% in simulation, 78.7% in phantom experiment, and 49.2% in in-vivo experiment. To evaluate the imaging performance of AZFsW, coherence factor, conventional Wiener postfilter, and scaled Wiener postfilter are implemented. The imaging results show that when σ is in the range of [0.6, 0.7], AZFsW exhibits a satisfying comprehensive imaging performance.
合成孔径（SA）成像可以提供均匀的横向分辨率，但信号噪声比（SNR）不足。具有双向像素聚焦（SA-BiPBF）的 SA 方法能够获得比传统 SA 成像更高质量的图像。在本文中，首先提出了一种名为全孔径接收远聚焦像素（FrFPB）的增强型 SA-BiPBF，以获得高分辨率图像。然后，在 FrFPB 中实现了可调零交叉因子缩放维纳后滤波器（AZFsW），以提高对比度（CR）。可调零交叉因子是使用回波信号序列的极性计算的，具有可调系数 σ，以估计信号相干性，并将其与维纳后滤波器相结合，以获得良好的降噪和背景散斑模式保留能力。已经进行了模拟和实验来评估所提出方法的成像性能。结果表明，与 SA-BiPBF 相比，FrFPB 可以明显提高分辨率，并且保留了对比度噪声比（CNR）和散斑信噪比（sSNR）。此外，AZFsW 可以实现比 SA-BiPBF 更高的 CR。当 σ 为 0.6 时，模拟中的 CR 提高了 96.7%，体模实验中的 CR 提高了 78.7%，体内实验中的 CR 提高了 49.2%。为了评估 AZFsW 的成像性能，实现了相干因子、传统维纳后滤波器和缩放维纳后滤波器。成像结果表明，当 σ 在 [0.6, 0.7] 范围内时，AZFsW 表现出令人满意的综合成像性能。
