Schweizer Dieter, Rau Richard, Bezek Can Deniz, Kubik-Huch Rahel A, Goksel Orcun
IEEE Trans Ultrason Ferroelectr Freq Control. 2023 Oct;70(10):1308-1318. doi: 10.1109/TUFFC.2023.3303172. Epub 2023 Oct 17.
Speed of sound (SoS) is a novel imaging biomarker for assessing the biomechanical characteristics of soft tissues. SoS imaging in the pulse-echo mode using conventional ultrasound (US) systems with hand-held transducers has the potential to enable new clinical uses. Recent work demonstrated that diverging waves (DWs) from a single element (SE) transmit to outperform plane-wave sequences. However, SE transmits have severely limited power and hence produce a low signal-to-noise ratio (SNR) in echo data. We herein propose Walsh-Hadamard (WH) coded and virtual-source (VS) transmit sequences for the improved SNR in SoS imaging. We additionally present an iterative method of estimating beamforming (BF) SoS in the medium, which otherwise confounds SoS reconstructions due to beamforming inaccuracies in the images used for reconstruction. Through numerical simulations, phantom experiments, and in vivo imaging data, we show that WH is not robust against motion, which is often unavoidable in clinical imaging scenarios. Our proposed VS sequence is shown to provide the highest SoS reconstruction performance, especially robust to motion artifacts. In phantom experiments, despite having a comparable SoS root-mean-square error (RMSE) of 17.5-18.0 m/s at rest, with a minor axial probe motion of ≈ 0.67 mm/s the RMSE for SE, WH, and VS already deteriorate to 20.2, 105.4, and 19.0 m/s, respectively, showing that WH produces unacceptable results, not robust to motion. In the clinical data, the high SNR and motion resilience of VS sequences are seen to yield superior contrast compared to SE and WH sequences.
声速（SoS）是一种用于评估软组织生物力学特性的新型成像生物标志物。使用带有手持换能器的传统超声（US）系统以脉冲回波模式进行的SoS成像有潜力实现新的临床应用。最近的研究表明，来自单个元件（SE）的发散波（DWs）传输性能优于平面波序列。然而，SE传输的功率严重受限，因此在回波数据中产生低信噪比（SNR）。我们在此提出沃尔什 - 哈达玛（WH）编码和虚拟源（VS）传输序列，以提高SoS成像中的SNR。我们还提出了一种在介质中估计波束形成（BF）SoS的迭代方法，否则由于用于重建的图像中的波束形成不准确，会混淆SoS重建。通过数值模拟、体模实验和体内成像数据，我们表明WH对运动不稳健，而运动在临床成像场景中往往不可避免。我们提出的VS序列显示出提供最高的SoS重建性能，尤其对运动伪影具有鲁棒性。在体模实验中，尽管在静止时SoS均方根误差（RMSE）相当，为17.5 - 18.0 m/s，但当轴向探头有≈0.67 mm/s的微小运动时，SE、WH和VS的RMSE分别恶化到20.2、105.4和19.0 m/s，表明WH产生不可接受的结果，对运动不稳健。在临床数据中，与SE和WH序列相比，VS序列的高SNR和运动弹性显示出产生更好的对比度。
