Dept. of Biomedical Engineering, University of Virginia, United States.
Ultrasonics. 2012 Mar;52(3):387-401. doi: 10.1016/j.ultras.2011.09.005. Epub 2011 Sep 22.
This paper proposes a novel receive beamformer architecture for broadband imaging systems that uses unique finite impulse response (FIR) filters on each channel. The conventional delay-and-sum (DAS) beamformer applies receive apodization by weighting the signal on each receive channel prior to beam summation. Our proposed FIR beamformer passes the focused receive radio frequency (RF) signals through multi-tap FIR filters on each receive channel prior to summation. The receive FIR filters are constructed to maximize the contrast resolution of the system's spatial response. The broadband FIR beamformer produces spatial point spread functions (PSFs) with narrower mainlobe widths and lower sidelobe levels than spatial PSFs produced by the conventional DAS beamformer. We present simulation results showing that FIR filters of modest tap lengths (3-7) can yield marked improvement in image contrast and point resolution. Specifically we show that 7-tap FIR filters can reduce sidelobe and grating lobe energy by 30dB and improve contrast resolution by as much as 20dB compared to conventional apodization profiles. This improvement in contrast resolution comes at the expense of a decrease in beamformer sensitivity. We investigate the effects of phase aberration and show in simulation results that the multi-tap FIR beamformer outperforms the unaberrated DAS beamformer by 8-12dB even in the presence of moderate aberration characterized by a root-mean-square strength of 28ns and a full-width at half-maximum correlation length of 3.6mm. We show experimental results wherein multi-tap FIR filters decrease sidelobe energy in the resulting 2D spatial response while achieving a narrow mainlobe. We also show results where the FIR beamformer improves the contrast to noise ratio (CNR) in simulated B-mode cyst images by more than 4dB. Our algorithm has the potential to significantly improve ultrasound beamforming in any application where the system response is reasonably well characterized. Furthermore, this algorithm can be used to increase contrast and resolution in one-way beamforming systems such as acousto-optic and opto-acoustic imaging.
本文提出了一种新颖的宽带成像系统接收波束形成器架构，该架构在每个通道上使用独特的有限脉冲响应（FIR）滤波器。传统的延迟和求和（DAS）波束形成器通过在波束求和之前对每个接收通道上的信号进行接收加权来应用接收加权。我们提出的 FIR 波束形成器在求和之前通过在每个接收通道上的多抽头 FIR 滤波器传递聚焦的接收射频（RF）信号。接收 FIR 滤波器的构造旨在最大化系统空间响应的对比度分辨率。与传统的 DAS 波束形成器产生的空间 PSF 相比，宽带 FIR 波束形成器产生的空间点扩散函数（PSF）具有更窄的主瓣宽度和更低的旁瓣电平。我们提出了仿真结果，表明具有适度抽头长度（3-7）的 FIR 滤波器可以显著提高图像对比度和点分辨率。具体来说，我们表明 7 抽头 FIR 滤波器可以将旁瓣和栅瓣能量降低 30dB，并将对比度分辨率提高多达 20dB，与传统的加权轮廓相比。这种对比度分辨率的提高是以波束形成器灵敏度降低为代价的。我们研究了相位像差的影响，并在仿真结果中表明，即使在具有以 RMS 强度为 28ns 和半最大值相关长度为 3.6mm 为特征的中等像差的情况下，多抽头 FIR 波束形成器也比无像差的 DAS 波束形成器好 8-12dB。我们展示了实验结果，其中多抽头 FIR 滤波器在产生的 2D 空间响应中降低了旁瓣能量，同时实现了窄主瓣。我们还展示了 FIR 波束形成器在模拟 B 模式囊肿图像中使对比度噪声比（CNR）提高超过 4dB 的结果。我们的算法有可能在系统响应相当准确的情况下，显著改善任何应用中的超声波束形成。此外，该算法可用于提高声光和光声成像等单向波束形成系统的对比度和分辨率。
