Tapering of the interventricular septum can affect ultrasound shear wave elastography: An in vitro and in silico study

Abstract

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 IVSmimicking 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.

Impact of shear wave dispersion slope analysis for assessing the severity of myocarditis

“…However, there are several issues to be resolved. Cardiac geometry is reported to be affected when measuring SW propagation 30 . Furthermore, although patients with fulminant myocarditis often have sinus tachycardia or tachyarrhythmias, the appropriate heart rate for assessing SW imaging is unclear.…”

Assessing cardiac stiffness using ultrasound shear wave elastography

“…LV phantom experiments and simulations have shown that the TOF method can underestimate the true stiffness up to 35% for ARF-based SWE depending on wall thickness and echocardiographic view (Caenen et al 2017). A recent study also investigated the effect of the thickness variations of the cardiac wall in simulations, showing a similar shear stiffness error for ARF-based SWE and an error of up to 65% for natural SWE (Sabbadini et al 2021). The Lamb wave theory on waves in plates has been used to better understand the geometrical effect on cardiac shear wave propagation and to improve shear wave characterization methods, on which more information can be found in the appendix.…”