Izadi Seyed Amin, Mahloojifar Ali, Asl Babak Mohammadzadeh
Department of Biomedical Engineering, Tarbiat Modares University, Ale-Ahmad Avenue, P.o. Box 14115-194, Tehran, Islamic Republic of Iran.
J Med Ultrason (2001). 2015 Oct;42(4):477-88. doi: 10.1007/s10396-015-0640-6. Epub 2015 Jul 28.
Capon-based beamformers are well-known methods to improve the SNR and quality of medical ultrasound images. Furthermore, they can improve the resolution of the images unexpectedly more than conventional DAS beamformers. Another method used in radar, sonar, and ultrasound imaging to increase the SNR is coded excitation with linear frequency-modulated signal (chirp).
In this paper, we illustrate that the combination of coded excitation with a Capon beamformer provides better resolution and higher SNR. However, this combination suffers from high sidelobe levels. We propose a weighted Capon beamformer (WCB) with chirp excitation to suppress the sidelobes and obtain a higher contrast with approximately the same resolution as the standard Capon beamformer (SCB). The weights of the WCB are obtained using element-wise multiplication of the weights of the SCB and a desired window (Hanning) with the same dimension.
The results show a 20 dB reduction in the sidelobe levels in simulated point targets and a 6 dB increase in background contrast in simulated cyst phantoms.
基于卡彭的波束形成器是提高医学超声图像信噪比和质量的知名方法。此外，它们能比传统延迟相加波束形成器更意外地提高图像分辨率。雷达、声纳和超声成像中用于提高信噪比的另一种方法是线性调频信号（啁啾）编码激励。
在本文中，我们表明编码激励与卡彭波束形成器的组合可提供更好的分辨率和更高的信噪比。然而，这种组合存在高旁瓣电平的问题。我们提出一种带啁啾激励的加权卡彭波束形成器（WCB），以抑制旁瓣，并在与标准卡彭波束形成器（SCB）大致相同的分辨率下获得更高的对比度。WCB的权重通过将SCB的权重与相同尺寸的期望窗口（汉宁窗）进行逐元素相乘得到。
结果显示，在模拟点目标中旁瓣电平降低了20 dB，在模拟囊肿模型中背景对比度提高了6 dB。
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