[论文解读] Ultrasound imaging with three dimensional full-wave nonlinear acoustic simulations. Part 2: sources of image degradation in intercostal imaging

Gianmarco Pinton|arXiv (Cornell University)|Mar 15, 2020

Microwave Imaging and Scattering Analysis参考文献 14被引用 4

一句话总结

本研究利用三维全波非线性超声仿真，探究肋间超声成像中的图像退化问题，发现尽管肋骨作为波束孔径调制器可改善旁瓣抑制，但同时也产生多重多次回波杂波，导致图像质量下降。当肋骨处于解剖学正常位置时，图像质量最优，此时孔径调制的益处与多次回波的代价达到平衡；当肋骨被人为压缩时，由于多次回波增加，对比噪声比（CNR）下降8%。

ABSTRACT

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.

研究动机与目标

• 识别肋间超声成像中图像退化的主要来源，特别是波前畸变和多次回波的影响。
• 通过体内无法实现的计算机仿真，分离肋骨结构对波束成形和多次回波的影响。
• 评估肋骨位置——特别是更紧密的间距——对图像质量指标（如对比噪声比，CNR）的影响。
• 证明仅凭波束轮廓不足以预测图像质量，而多次回波是主导且常被低估的关键因素。
• 验证Fullwave仿真平台作为复杂、非均质解剖环境中定量图像质量分析工具的有效性。

提出的方法

• 基于非均质介质中波动传播基本原理的三维全波仿真，用于模拟肋间窗口的超声成像。
• 仿真采用可见人女性尸体数据集的解剖数据，生成胸腔的逼真三维声学图。
• 模拟了三种成像场景：移除肋骨并以脂肪替代、肋骨处于解剖学位置、肋骨在垂直方向上人为压缩。
• 计算点扩散函数（PSFs）以分离并量化多次回波杂波与其他图像退化源的影响。
• 通过测量B型图像中的对比噪声比（CNR）来评估三种场景下的图像质量。
• 利用波束图和PSF分析，分离波前畸变、孔径调制和多次回波对图像质量的影响。

实验结果

研究问题

• RQ1 肋骨引起的波前畸变与多次回波对肋间超声图像退化的影响，其相对贡献如何？
• RQ2 肋骨位置——特别是更紧密的间距——如何影响波束形状和图像质量指标（如CNR）？
• RQ3 尽管引入了额外的多次回波杂波，肋骨的波束孔径调制是否仍能改善图像质量？
• RQ4 为何当肋骨被移近时，图像质量会下降，即使波束轮廓显示旁瓣抑制得到改善？
• RQ5 波束轮廓和波前畸变本身在多大程度上能预测图像质量？还是说多次回波是主导且未被充分考虑的关键因素？

主要发现

• 解剖学上正确的肋骨配置在尽管导致3–5 dB孔径调制损失的情况下，仍实现了最高的对比噪声比（CNR），表明图像质量总体得到改善。
• 当肋骨被移除并替换为脂肪时，CNR相比解剖学情况下降8%，尽管波束形状得到改善，但这是由于孔径调制作用的丧失。
• 将肋骨人为压缩几毫米可改善波束旁瓣抑制，但使多次回波杂波增加2.4–2.9 dB，整体CNR因此下降。
• 通过PSF量化了多次回波杂波：在基频下，其电平从解剖学肋骨的-35.4 dB上升至压缩肋骨的-32.7 dB。
• 在二次谐波下，多次回波杂波从解剖学情况的-51.2 dB上升至压缩情况的-48.9 dB，证实当肋骨间距变小时，多次回波是主导的图像退化因素。
• 本研究证明，仅依靠波束轮廓和波前畸变无法充分预测图像质量；多次回波是肋间成像中一个关键且常被低估的影响因素。