## 4 Discussion
### Recommendations and Impact for Other Applications  
The dispersive shear wave propagation pattern studied here is inherently linked to the considered setting, i.e., a left ventricular low viscous phantom with pediatric geometry. We focused on the isolated effect of guided wave dispersion due to geometry, and therefore, the formulated conclusions cannot simply be extrapolated to actual tissue settings as dispersion in tissues can be caused by a combination of varying factors such as geometry, viscosity and non-homogeneous (potentially anisotropic) material characteristics. This is among other things noticeable in the excited frequency range of the studied shear wave (up to 2 kHz), which is much larger than the conventional 1 kHz shear wave frequency spectra reported in real tissue settings due to tissue's high shear viscosity [17]. Additionally, the observed shear wave fronts were quite isotropic in all directions of the shear wave paths in 2D, whereas these will become guided along the fiber orientation in anisotropic tissue [45; 46]. These true tissue characteristics demand more advanced tissue characterization algorithms as now (i) an isotropic bulky elastic material is assumed in the group speed analysis in order to apply Formula (4), and (ii) a theoretical dispersion curve of an isotropic homogeneous elastic plate in water is used as fitting ground truth in the phase speed analysis. Therefore, complementary research is necessary to investigate how the formulated conclusions concerning shear wave visualization and characterization are translated to actual tissue settings in vivo, particularly when assessing the effect of compounding.  
Despite these dissimilarities between shear wave physics in the phantom-model and actual tissue, the multiphysics model of the presented case study allowed the assessment of the effect of ultrafast imaging on shear wave visualization and characterization from a mechanical point of view, as described in the previous section. Furthermore, this study showed that the number of compounding angles (i.e., the factor with which the frame rate is reduced) should be chosen taking the maximal reachable PRF (linked to imaged depth and technical capabilities of the ultrasound system), the wave propagation speed of the investigated material (related to its mechanical properties) and the bandwidth of the imaged phenomenon (related to different absorption mechanisms such as viscosity) into account. The resulting compounded frame rate should be sufficiently high to obtain an accurate representation of the mechanical shear wave physics, which was not the case for the studied left ventricular phantom model. Additionally, a high frame rate is also desirable from the shear wave characterization point of view, as this means a high Nyquist cut-off frequency, providing a more extensive Fourier spectrum, and thus a more reliable stiffness estimate via the phase velocity analysis.  
Similar recommendations were recently published by [PERSON] et al. [19], who studied the optimal ARF and imaging settings to maximize bandwidth for phase velocity analysis in SWE on ex vivo arterial settings. In their study on arterial stiffness estimation, they claimed that a high PRF with poorer image quality is more desirable than a lower PRF with better image quality.