Local Sound Speed Estimation for Pulse-Echo Ultrasound in Layered Media.
Local Sound Speed Estimation for Pulse-Echo Ultrasound in Layered Media.
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DOI：
10.1109/tuffc.2021.3124479
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发表时间：
2022-03
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我们以前的方法在本地声速估计利用延迟的全合成孔径通道数据的互相关测量的时间延迟来估计平均声速。然而，这种方法中的焦点失真导致对平均声速的有偏估计，这反过来又导致对局部声速的有偏估计。在这里，我们证明了在以前的方法的偏见，并介绍了一个基于相干的平均声速估计，消除这种偏见，是在实践中计算便宜得多。由于这种基于相干性的方法估计平均声速在介质中的深度，而不是时间上的等距网格，我们得到一个完善的模型，涉及的本地和平均声速作为分层介质中的深度的函数。该模型的快速，封闭形式的反演产生高度准确的局部声速估计。在4和8 MHz时，双层介质模拟中局部声速重建的均方根（RMS）误差分别为4.6和2.5 m/s。这项工作探讨了频率，f数，畸变和混响对声速估计的影响。大鼠体模和体内实验进一步验证了基于相干性的声速估计器。
Our previous methodology in local sound speed estimation utilized time delays measured by the cross-correlation of delayed full synthetic aperture channel data to estimate the average speed of sound. However, focal distortions in this methodology lead to biased estimates of the average speed of sound, which, in turn, leads to biased estimates of the local speed of sound. Here, we demonstrate the bias in the previous methodology and introduce a coherence-based average sound speed estimator that eliminates this bias and is computationally much cheaper in practice. Because this coherence-based approach estimates the average sound speed in the medium over an equally-spaced grid in depth rather than time, we derive a refined model that relates the local and average speeds of sound as a function of depth in layered media. A fast, closed-form inversion of this model yields highly accurate local sound speed estimates. The root mean-square (RMS) error of local sound speed reconstruction in simulations of two-layer media is 4.6, and 2.5 m/s at 4 and 8 MHz, respectively. This work examines the impact of frequency, f-number, aberration, and reverberation on sound speed estimation. Phantom and in-vivo experiments in rats further validate the coherence-based sound speed estimator.