In vivo open- and closed-chest measurements of left-ventricular myocardial viscoelasticity using lamb wave dispersion ultrasound vibrometry (LDUV): a feasibility study

Abstract

Diastolic dysfunction causes close to half of congestive heart failures and is associated with increased stiffness in left-ventricular myocardium. A clinical tool capable of measuring viscoelasticity of the myocardium could be beneficial in clinical settings. We used Lamb wave Dispersion Ultrasound Vibrometry (LDUV) for assessing the feasibility of making in vivo non-invasive measurements of myocardial elasticity and viscosity in pigs. In vivo open-chest measurements of myocardial elasticity and viscosity obtained using a Fourier space based analysis of Lamb wave dispersion are reported. The approach was used to perform ECG-gated transthoracic in vivo measurements of group velocity, elasticity and viscosity throughout a single heart cycle. Group velocity, elasticity and viscosity in the frequency range 50–500 Hz increased from diastole to systole, consistent with contraction and relaxation of the myocardium. Systolic group velocity, elasticity and viscosity were 5.0 m/s, 19.1 kPa, 6.8 Pa·s, respectively. In diastole, the measured group velocity, elasticity and viscosity were 1.5 m/s, 5.1 kPa and 3.2 Pa·s, respectively.

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

“…These studies showed that such higher modes, which only appear above well-defined values of the frequency-thickness product, can be reflected or converted into lower order modes when the thickness decreased sufficiently. However, the waves analysed in cardiac SWE have a relatively low frequency content (typically within 1000 Hz 19,22,27,28 ) and are therefore characterized mainly by the zero-order modes and the first-order modes: the former are present at all frequency-thickness products, and, for the latter, cardiac thickness reductions are not large enough for mode conversion. Therefore, the effects described in literature would be hardly observed in the context of cardiac SWE.…”

“…In principle, analysing the propagation data in the f-k domain should provide a more robust method of deriving G, since fitting the dispersion curves allows one to determine the value of the bulk shear speed, which is directly related to the shear modulus. 4,11,19,20,26,27 However, as is apparent from Tables I and II, knowledge on the specific shape of the observed IVS is necessary in order to perform the fit correctly. Our results show, in fact, that neglecting the thickness variations can lead to considerable overestimation and underestimation of the shear modulus, and that a significant role is played by the exact shape of the plate, as opposed to the overall thickness reduction.…”

“…17,18 Efforts have been made in the cardiac SWE field to account for the dispersive behaviour of the wave in the material characterization algorithms. Instead of studying the wave propagation characteristics in the space-time (x-t) domain, various studies 4,19,20,26,27 have analysed waves in the frequency-wavenumber (f-k) domain to reconstruct the dispersion curves. When approaching the IVS as a fluidloaded elastic plate, the shear modulus can be extracted by fitting a theoretical Lamb wave dispersion curve to the experimental ones.…”

“…In fact, it has already been shown that, when the slowly varying thickness of a waveguide reaches the frequency-thickness cut-off of a certain mode, mode conversion and reflections take place. [32][33][34] Interestingly, natural and ARF-generated waves are expected to be affected differently by the thickness variation, due to their different frequency contents (up to around 150 Hz and 1000 Hz, respectively 19,22,27,28 ).…”

Parasternal Versus Apical View in Cardiac Natural Mechanical Wave Speed Measurements

“…However, Vos et al [21] only measured mild dispersion for SWs after AVC and MVC in pigs and, therefore, found a poor match with A 0 -Lamb wave modes. This same model was used in studies using external sources like an external shaker [10], [11], [34], [35], and ARF [33], [37]. However, it should be noted that when using an ARF source in a parasternal long-axis view, the load is directed perpendicular to the myocardium, inducing, therefore, mainly the transversal particle motion (and thus the A 0 -mode).…”