## 5 Discussion
\begin{table}
\begin{tabular}{c c c} \hline
**Technique** & **Advantage** & **Limitation** \\ \hline ASQ imaging & Have been commercialized & \begin{tabular}{c} Inconsistent findings for characterizing \\ human hepatic steatosis \\ \end{tabular} \\ \hline Ultrasound Nakagami imaging & Low computational complexity & \
\begin{tabular}{c} The \(m\) parameter plateaus \\ around 1 for higher scatterer concentrations \\ \end{tabular} \\ \hline Ultrasound HK imaging & Have a physical meaning & High analytical complexity \\ \hline Ultrasound kurtosis imaging & Easy to compute & Need further validation \\ \hline Ultrasound entropy imaging &
\begin{tabular}{c} Allow a small-window \\ (high-resolution) imaging \\ \end{tabular} & The dynamic range of Shannon entropy \\ is limited \\ \hline \end{tabular}
\end{table} 
Table 2: Comparison of ultrasound envelope statistics parametric imaging techniques. between different ultrasound envelope statistics parametric imaging techniques are expected in future developments. The size of the sliding windows (Figure 2) has an impact on ultrasound envelope statistics parametric imaging. Using a large window to construct a parametric image results in stable parameter estimation and enhanced image smoothness. By contrast, a small window (corresponding to a small spatial scale) enables the achievement of enhanced envelope statistics parametric image resolution. The effects of the window size on envelope statistics parametric imaging of hepatic steatosis should be investigated in future developments. The estimators for estimating envelope statistics parameters also can affect the performance of ultrasound envelope statistics parametric imaging of hepatic steatosis. Different estimators should be compared, and new estimators can be developed. In addition, new envelope statistics parameters and associated parametric imaging methods can be explored in future developments. It would be interesting to investigate the relationship of envelope statistics to other QUS parameters such as tissue elasticity, so that a better characterization of tissue microstructures can be realized. Additionally, combination of different envelope statistics parametric imaging techniques, and combination of envelope statistics parametric imaging techniques with other QUS imaging techniques may be explored in future developments, in order to improve the performance of hepatic steatosis characterization. For instance, a recent study combined HK imaging with ultrasound elastography for a better characterization of nonalcoholic steatohepatitisitis of a rat model [54]. Investigating three-dimensional envelope statistics parametric imaging can provide more complete information and clues related to hepatic steatosis. Compared with one-dimensional or two-dimensional envelope statistics parametric imaging, three-dimensional envelope statistics parametric imaging can offer an enhanced characterization of hepatic steatosis, which involves the construction of the three-dimensional envelope statistics parametric image. Currently, only three-dimensional Nakagami imaging has been proposed for hepatic steatosis assessment [19]. Three-dimensional parametric imaging based on other envelope statistics parameters can be explored for characterizing hepatic steatosis in future developments. Conceptualization, Z.Z., S.W., and P.-H.T. ; investigation, Z.Z., Q.Z., and W.W.; writing--original draft preparation, Z.Z., Q.Z., and W.W.; writing--review and editing, S.W. and P.-H.T. ; project administration, S.W. and P.-H.T. ; funding acquisition, Z.Z., W.W., and S.W. This work was supported in part by the National Natural Science Foundation of China (Grant Nos. 11804013, 61871005, 71661167001, and 61801312), the Beijing Natural Science Foundation (Grant No. 4184081), the International Research Cooperation Seed Fund of Beijing University of Technology (Grant No.