Deylami Ali Mohades, Asl Babak Mohammadzadeh
Department of Biomedical Engineering, Tarbiat Modares University, Jalal Ale Ahmad Highway, P.O. Box 14115-111, Tehran, Iran.
J Med Ultrason (2001). 2016 Jan;43(1):11-8. doi: 10.1007/s10396-015-0671-z. Epub 2015 Oct 5.
The adaptive amplitude and phase estimator (APES) has been introduced in medical ultrasound imaging to calculate the amplitude of the desired signal more robustly than other adaptive beamformers like minimum variance (MV). This beamformer minimizes the optimization problem of MV by replacing the estimated array covariance matrix by the interferences plus noise covariance matrix. On the other hand, the Wiener postfilter as a post-weighting factor, which will be multiplied to the final weight vector of the beamformer, estimates the power of the desired signal and the power of the interferences plus noise to improve the contrast.
The proposed method is a combination of the APES beamformer with the Wiener postfilter which uses the capabilities of the APES beamformer for accurate estimation of the amplitude of the desired signal and the Wiener postfilter in suppressing sidelobes. Specifically, we used the interferences plus the noise covariance matrix estimated in the APES beamformer to obtain an APES-based Wiener postfilter and obtained the APES + Wiener weight vector by multiplying the APES-based Wiener postfilter to the standard APES weight vector.
To evaluate the proposed APES + Wiener beamformer, we tested the proposed method on simulated and experimental datasets. The results of a simulated wire phantom demonstrate that the proposed beamformer can resolve two point scatterers better than the standard APES beamformer, even if the points are placed near each other. Simulating a cyst phantom shows that the APES + Wiener beamformer improves the contrast of the resulting images by about 4.5 dB by estimating the interior of the cyst better than the standard APES.
The evaluation of the proposed beamformer on an experimental dataset confirms the results of simulations, in which the proposed beamformer improves the resolution and contrast in comparison with the standard APES beamformer.
自适应幅度和相位估计器（APES）已被引入医学超声成像领域，用于比最小方差（MV）等其他自适应波束形成器更稳健地计算期望信号的幅度。这种波束形成器通过用干扰加噪声协方差矩阵替换估计的阵列协方差矩阵，最小化了MV的优化问题。另一方面，维纳后置滤波器作为一个后置加权因子，将与波束形成器的最终权重向量相乘，估计期望信号的功率以及干扰加噪声的功率，以提高对比度。
所提出的方法是APES波束形成器与维纳后置滤波器的结合，它利用APES波束形成器准确估计期望信号幅度的能力以及维纳后置滤波器抑制旁瓣的能力。具体而言，我们使用在APES波束形成器中估计的干扰加噪声协方差矩阵来获得基于APES的维纳后置滤波器，并通过将基于APES的维纳后置滤波器与标准APES权重向量相乘来获得APES + 维纳权重向量。
为了评估所提出的APES + 维纳波束形成器，我们在模拟和实验数据集上测试了该方法。模拟线体模的结果表明，即使两点散射体彼此靠近放置，所提出的波束形成器也能比标准APES波束形成器更好地分辨它们。模拟囊肿体模表明，APES + 维纳波束形成器通过比标准APES更好地估计囊肿内部，将所得图像的对比度提高了约4.5 dB。
在所提出的波束形成器在实验数据集上的评估证实了模拟结果，其中所提出的波束形成器与标准APES波束形成器相比提高了分辨率和对比度。
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