三维全波非线性声学模拟超声成像。第2部分：肋间成像中图像退化的来源
Ultrasound imaging with three dimensional full-wave nonlinear acoustic simulations. Part 2: sources of image degradation in intercostal imaging
摘要：
全波模拟应用于肋间成像的情况下，以确定基本和谐波图像退化的畸变和混响的来源。这些模拟是基于这两部分论文的第一部分，其中建立了全波模拟方法，直接基于波在人体中传播的第一原理生成逼真的超声图像。超声波图像是基于传播和反射的第一性原理产生的，它们描述了分布畸变和混响杂波之间的相互作用。三个成像方案，将无法实现在体内进行了研究，在硅片。首先，肋骨被完全切除，取而代之的是脂肪。然后，将肋骨保持在其解剖学上正确的构型以产生参考图像。最后，肋骨在高度上被放置得更靠近。基于传播的B模式图像显示，在这三种情况中，第二种情况（解剖学上正确的配置）具有最佳的对比度噪声比。这是由于两个相互竞争的影响。首先，肋有效地使基波和谐波波束变迹3- 5dB。仅此效应就可预测图像质量的改善。然而，通过对比度噪声比测量的B模式图像质量降低了8%。为了解释这些变化，它表明，第二个效果，多混响，必须考虑。点扩散函数分析表明，当肋骨放置得更靠近时，它们会产生明显更多的混响杂波（2.4至2.9 dB），即使波束图具有较低的旁瓣，也会降低图像质量。在这种肋间成像场景中，肋骨对波束形状和混响的影响因此在图像质量方面存在竞争，并且存在平衡它们的最佳声学窗口。
英文摘要：
Fullwave simulations are applied to an intercostal imaging scenario to determine the sources of fundamental and harmonic image degradation with respect to aberration and reverberation. These simulations are based on Part I of this two part paper, which established the Fullwave simulation methods to generate realistic ultrasound images based directly on the first principles of wave propagation in the human body. The ultasound images are generated based on the first principles of propagation and reflection and they describe interplay between distributed aberration and reverberation clutter. Three imaging scenarios that would not be realizable in vivo are investigated in silico. First, the ribs were completely removed and replaced with fat. Then, the ribs were maintained in their anatomically correct configuration to yield a reference image. Finally the ribs were placed closer together in elevation. The propagation based B-mode images show that of these three scenarios the second, anatomically correct configuration, has the best contrast-to-noise ratio. This is due to two competing effects. First the ribs effectively apodize the fundamental and harmonic beams by 3-5 dB. This effect alone would predict an improvement in image quality. However, the B-mode image quality, measured by the contrast-to-noise ratio degrades by 8%. To explain these changes, it is shown that a second effect, multiple reverberation, must be taken into account. A point spread function analysis shows that when the ribs are placed closer together they generate significantly more reverberation clutter (by 2.4 to 2.9 dB), degrading the image quality even though the beamplot has lower sidelobes. In this intercostal imaging scenario the effects of the ribs on beam shape and reverberation are therefore in competition in terms of image quality and there is an optimal acoustic window that balances them out.
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