Shear wave elastography (SWE) has the potential to determine cardiac tissue stiffness from non-invasive shear wave speed measurements, important, e.g., for predicting heart failure. Previous studies showed that waves traveling in the interventricular septum (IVS) may display Lamb-like dispersive behaviour, introducing a thickness-frequency dependency in the wave speed. However, the IVS tapers across its length, which complicates wave speed estimation by introducing an additional variable to account for. The goal of this work is to assess the impact of tapering thickness on SWE. The investigation is performed by combining in vitro experiments with acoustic radiation force (ARF) and 2D finite element simulations, to isolate the effect of the tapering curve on ARF-induced and natural waves in the heart. The experiments show a 11% deceleration during propagation from the thick to the thin end of an IVS-mimicking tapered phantom plate. The numerical analysis shows that neglecting the thickness variation in the wavenumber-frequency domain can introduce errors of more than 30% in the estimation of the shear modulus, and that the exact tapering curve, rather than the overall thickness reduction, determines the dispersive behaviour of the wave. These results suggest that septal geometry should be accounted for when deriving cardiac stiffness with SWE.

中文翻译：

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室间隔变细会影响超声剪切波弹性成像：体外和硅片研究

剪切波弹性成像 (SWE) 具有从非侵入性剪切波速度测量中确定心脏组织硬度的潜力，这对于预测心力衰竭很重要。先前的研究表明，在室间隔 (IVS) 中传播的波可能会表现出类似 Lamb 的色散行为，从而在波速中引入厚度-频率依赖性。然而，IVS 在其长度上逐渐变细，这通过引入一个额外的变量来解释波速估计变得复杂。这项工作的目的是评估逐渐变细的厚度对 SWE 的影响。该研究是通过结合体外进行的使用声辐射力 (ARF) 和 2D 有限元模拟进行实验，以隔离锥形曲线对 ARF 诱导的心脏波和自然波的影响。实验表明，在 IVS 模拟锥形体模板从厚端到薄端的传播过程中减速了 11%。数值分析表明，忽略波数-频域中的厚度变化会在剪切模量的估计中引入超过 30% 的误差，并且精确的锥形曲线，而不是整体厚度减少，决定了材料的色散行为海浪。这些结果表明，在使用 SWE 推导心脏硬度时，应考虑间隔几何形状。