Department of Robotics and Mechatronics, AGH University of Science and Technology, 30-059 Krakow, Poland.
Department of Radiology, Mayo Clinic, Rochester, MN 55905, USA; Department of Physiology and Biomedical Engineering, Mayo Clinic, Rochester, MN 55905, USA.
Ultrasonics. 2022 Aug;124:106735. doi: 10.1016/j.ultras.2022.106735. Epub 2022 Mar 29.
Quantitative assessment of mechanical properties of biological soft tissues is frequently evaluated using a noninvasive modality, called ultrasound shear wave elastography (SWE). SWE typically exerts an acoustic radiation force (ARF) to produce shear waves propagating in the lateral direction for which velocities and attenuations are measured. The tissue viscoelasticity is commonly studied by investigating the shear wave phase velocity curves. Viscoelastic tissue properties can also be characterized through utilizing various shear wave attenuation techniques. In this study, we propose an improved method for measuring the shear wave attenuation, called two-point frequency shift power (2P-FSP), which is an improved version of the two-point frequency shift (2P-FS) method. The technique is fully data driven and does not use a rheological model for mathematical modeling. The 2P-FSP method utilizes the power spectra frequency shift of shear waves measured at two spatial positions, which provides robustness to noise. The conceptual basis for the 2P-FSP is provided and tested with numerical and experimental data. We investigated how the location of the first signal and the distance interval between the two locations influence the shear wave attenuation measurement in the 2P-FSP technique. We utilized the 2P-FSP method on numerical phantom data generated using a finite-difference-based method in tissue-mimicking viscoelastic media. Moreover, we tested the 2P-FSP method with data from custom-made tissue-mimicking viscoelastic phantom experiments, and ex vivo porcine liver. We compared results from the proposed technique with results from 2P-FS and analytical values in the case of simulations. The results showed that the 2P-FSP method provides improved results over the 2P-FS technique for lower signal-to-noise ratio (SNR) and locations farther from the push location considered, and can be used to measure attenuation of viscoelastic soft tissues.
生物软组织力学性能的定量评估通常采用一种称为超声剪切波弹性成像（SWE）的非侵入性方式进行。SWE 通常施加声辐射力（ARF）以产生在横向传播的剪切波，测量其速度和衰减。组织粘弹性通常通过研究剪切波相速度曲线来研究。还可以通过利用各种剪切波衰减技术来表征粘弹性组织特性。在这项研究中，我们提出了一种改进的剪切波衰减测量方法，称为两点频移功率（2P-FSP），它是两点频移（2P-FS）方法的改进版本。该技术完全是数据驱动的，不需要使用流变学模型进行数学建模。2P-FSP 方法利用在两个空间位置测量的剪切波的功率谱频移，这为噪声提供了稳健性。提供了 2P-FSP 的概念基础，并使用数值和实验数据进行了测试。我们研究了在 2P-FSP 技术中，第一信号的位置和两个位置之间的距离间隔如何影响剪切波衰减测量。我们利用基于有限差分的方法在组织模拟粘弹性介质中生成的数值体模数据来测试 2P-FSP 方法。此外，我们还使用来自定制的组织模拟粘弹性体模实验和离体猪肝的数据测试了 2P-FSP 方法。我们将提出的技术的结果与模拟情况下的 2P-FS 技术和分析值的结果进行了比较。结果表明，与 2P-FS 技术相比，2P-FSP 方法在较低的信噪比（SNR）和远离推压位置的位置下提供了更好的结果，并且可以用于测量粘弹性软组织的衰减。
