Chen Yuling, Lou Yang, Yen Jesse
1 Zonare Medical Systems/Mindray North America Innovation Center, Mountain View, California, USA.
2 University of Southern California, Los Angeles, California, USA.
Ultrason Imaging. 2017 Jul;39(4):207-223. doi: 10.1177/0161734617692017. Epub 2017 Mar 1.
During conventional ultrasound imaging, the need for multiple transmissions for one image and the time of flight for a desired imaging depth limit the frame rate of the system. Using a single plane wave pulse during each transmission followed by parallel receive processing allows for high frame rate imaging. However, image quality is degraded because of the lack of transmit focusing. Beamforming by spatial matched filtering (SMF) is a promising method which focuses ultrasonic energy using spatial filters constructed from the transmit-receive impulse response of the system. Studies by other researchers have shown that SMF beamforming can provide dynamic transmit-receive focusing throughout the field of view. In this paper, we apply SMF beamforming to plane wave transmissions (PWTs) to achieve both dynamic transmit-receive focusing at all imaging depths and high imaging frame rate (>5000 frames per second). We demonstrated the capability of the combined method (PWT + SMF) of achieving two-way focusing mathematically through analysis based on the narrowband Rayleigh-Sommerfeld diffraction theory. Moreover, the broadband performance of PWT + SMF was quantified in terms of lateral resolution and contrast from both computer simulations and experimental data. Results were compared between SMF beamforming and conventional delay-and-sum (DAS) beamforming in both simulations and experiments. At an imaging depth of 40 mm, simulation results showed a 29% lateral resolution improvement and a 160% contrast improvement with PWT + SMF. These improvements were 17% and 48% for experimental data with noise.
在传统超声成像过程中，获取一幅图像需要多次发射，且对于所需成像深度的飞行时间限制了系统的帧率。在每次发射期间使用单个平面波脉冲，随后进行并行接收处理，可实现高帧率成像。然而，由于缺乏发射聚焦，图像质量会下降。通过空间匹配滤波（SMF）进行波束形成是一种很有前景的方法，它利用根据系统发射 - 接收脉冲响应构建的空间滤波器来聚焦超声能量。其他研究人员的研究表明，SMF波束形成可在整个视场提供动态发射 - 接收聚焦。在本文中，我们将SMF波束形成应用于平面波发射（PWT），以在所有成像深度实现动态发射 - 接收聚焦以及高成像帧率（>每秒5000帧）。我们基于窄带瑞利 - 索末菲衍射理论，通过分析从数学上证明了组合方法（PWT + SMF）实现双向聚焦的能力。此外，从计算机模拟和实验数据两方面，根据横向分辨率和对比度对PWT + SMF的宽带性能进行了量化。在模拟和实验中，将SMF波束形成与传统延迟求和（DAS）波束形成的结果进行了比较。在成像深度为40 mm时，模拟结果表明，使用PWT + SMF时横向分辨率提高了29%，对比度提高了160%。对于有噪声的实验数据，这些改进分别为17%和48%。
