Huang Yizhou, Chen Xufei, Badescu Emilia, Kuenen Maarten, Bonnefous Odile, Mischi Massimo
Lab. of Biomedical Diagnostics, Eindhoven University of Technology, Eindhoven, The Netherlands.
Lab. of Biomedical Diagnostics, Eindhoven University of Technology, Eindhoven, The Netherlands.
Ultrasonics. 2024 May;140:107307. doi: 10.1016/j.ultras.2024.107307. Epub 2024 Mar 26.
With the development of advanced clutter-filtering techniques by singular value decomposition (SVD) and leveraging favorable acquisition settings such as open-chest imaging by a linear high-frequency probe and plane waves, several studies have shown the feasibility of cardiac flow measurements during the entire cardiac cycle, ranging from coronary flow to myocardial perfusion. When applying these techniques in a routine clinical setting, using transthoracic ultrasound imaging, new challenges emerge. Firstly, a smaller aperture is needed that can fit between ribs. Consequently, diverging waves are employed instead of plane waves to achieve an adequate field of view. Secondly, to ensure imaging at a larger depth, the maximum pulse repetition frequency has to be reduced. Lastly, in comparison to the open-chest scenario, tissue motion induced by the heartbeat is significantly stronger. The latter complicates substantially the distinction between clutter and blood signals.
This study investigates a strategy to overcome these challenges by diverging wave imaging with an optimal number of tilt angles, in combination with dedicated clutter-filtering techniques. In particular, a novel, adaptive, higher-order SVD (HOSVD) clutter filter, which utilizes spatial, temporal, and angular information of the received ultrasound signals, is proposed to enhance clutter and blood separation.
When non-negligible tissue motion is present, using fewer tilt angles not only reduces the decorrelation between the received waveforms but also allows for collecting more temporal samples at a given ensemble duration, contributing to improved Doppler performance. The addition of a third angular dimension enables the application of HOSVD, providing greater flexibility in selecting blood separation thresholds from a 3-D tensor. This differs from the conventional threshold selection method in a 2-D spatiotemporal space using SVD. Exhaustive threshold search has shown a significant improvement in Contrast and Contrast-to-Noise ratio for Power Doppler images filtered with HOSVD compared to the SVD-based clutter filter.
With the improved settings, the obtained Power Doppler images show the feasibility of measuring coronary flow under the influence of non-negligible tissue motion in both in vitro and ex vivo.
随着通过奇异值分解（SVD）的先进杂波滤波技术的发展，并利用有利的采集设置，如使用线性高频探头和平面波进行开胸成像，多项研究已表明在整个心动周期中进行心脏血流测量的可行性，范围从冠状动脉血流到心肌灌注。当在常规临床环境中应用这些技术进行经胸超声成像时，会出现新的挑战。首先，需要一个较小的孔径以适合肋骨之间。因此，采用发散波而非平面波来获得足够的视野。其次，为确保在更大深度成像，必须降低最大脉冲重复频率。最后，与开胸情况相比，心跳引起的组织运动明显更强。后者极大地使杂波和血液信号的区分变得复杂。
本研究探讨了一种策略，即通过具有最佳倾斜角度数量的发散波成像与专用杂波滤波技术相结合来克服这些挑战。特别是，提出了一种新颖的、自适应的高阶SVD（HOSVD）杂波滤波器，它利用接收到的超声信号的空间、时间和角度信息来增强杂波和血液的分离。
当存在不可忽略的组织运动时，使用较少的倾斜角度不仅会降低接收到的波形之间的去相关性，还允许在给定的采集持续时间内收集更多的时间样本，有助于提高多普勒性能。增加第三个角度维度使得能够应用HOSVD，在从三维张量中选择血液分离阈值方面提供了更大的灵活性。这与在二维时空空间中使用SVD的传统阈值选择方法不同。详尽的阈值搜索表明，与基于SVD的杂波滤波器相比，用HOSVD滤波的功率多普勒图像在对比度和对比度噪声比方面有显著改善。
通过改进设置，所获得的功率多普勒图像显示了在体外和离体情况下，在不可忽略的组织运动影响下测量冠状动脉血流的可行性。
