## 4 Results
### Experimental Cyst Phantom  
Figure 6 shows the experimental cyst images. Regions indicated by two circles and boxes were selected to calculate the image quality metrics, the regions indicated by the cyan dashed lines were used to plot the lateral variations, and the point target indicated by the cyan box was used to calculate the FWHM. DMAS obtains an improved contrast over DAS, but degrades the background intensity significantly. The SLSC image shows enhanced lesion detection, but the point resolution is poor and some dark-region artifacts appears beside the point. CMSB images show an improved contrast and improved background intensity. In addition, LOCw-CMSB suppresses noises in the cyst at 42.9 mm depth compared with CMSB (\(\delta\) = 1.3), and also removes noise in the cyst at 15 mm depth compared with CMSB, with \(\delta\) equal to 0.7 and 1.3. This indicates that LOC weighting can effectively improve the contrast performance of CMSB. In addition, CMSB (\(\delta\) = \(\delta_{ac}\)) improves the speckle smoothness and intensity over CMSB (\(\delta\) = 1.3). Figure 5: Lateral variations through three points at the depth of (**a**) 9.6 mm, (**b**) 28.1 mm, and (**c**) 47 mm in the experimental point images. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Methods**} & \multicolumn{3}{c}{**FWHM (mm) at Depths of**} \\  & **9.6 mm** & **28.1 mm** & **47 mm** \\ \hline DAS & 0.55 & 0.56 & 0.57 \\ DMAS & 0.44 & 0.44 & 0.46 \\ CMSB (\(\delta\) = 0.7) & 0.29 & 0.32 & 0.51 \\ CMSB (\(\delta\) = 1.3) & 0.23 & 0.26 & 0.49 \\ LOCw-CMSB & 0.23 & 0.26 & 0.49 \\ CMSB (\(\delta\) = \(\delta_{ac}\)) & 0.23 & 0.27 & 0.56 \\ LOCw-CMSB (\(\delta\) = \(\delta_{ac}\)) & 0.23 & 0.27 & 0.56 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Lateral FWHM at three different depths in the experimental point images. Figure 7 plots the lateral variations through the point target indicated by the cyan box, and the two cyst targets are indicated by cyan dashed lines in the experimental cyst images. As can be seen, CMSB (\(\delta\) = 0.7) obtains a narrower mainlobe compared with DMAS, and other CMSB-based methods all obtain the narrowest mainlobe. This indicates the maintained resolution performance of enhanced CMSB methods. In addition, LOCw-CMSB and LOCw-CMSB (\(\delta\) = \(\delta_{ac}\)) obtain the lowest noise level in cyst targets, which is lower than that of DMAS, and have the best edge resolution according to Figure 7b,c. Table 4 lists image quality metrics of experimental cyst phantom images. The point targets at (\(x\),\(z\)) = (8 mm, 38 mm) were used to calculate FWHM. Note that the resolution of the SLSC is not calculated because the image is not log-compressed. SLSC obtains a lower contrast at a shallow depth but a higher contrast at a large depth compared with DAS, and SLSC obtains the highest gCNR and sSNR. The proposed methods preserve the resolution of CMSB (\(\delta\) = 1.3), which is a 41.3% improvement compared with DMAS. According to Table 4, CMSB obtains an improved CR, gCNR, and sSNR over DAS and  
Figure 6: Experimental cyst phantom images reconstructed by (**a**) DAS, (**b**) DMAS, (**c**) SLSC, (**d**) CMSB (\(\delta\) = 0.7), (**e**) CMSB (\(\delta\) = 1.3), (**f**) LOCw-CMSB, (**g**) CMSB (\(\delta\) = \(\delta_{ac}\)), and (**h**) LOCw-CMSB (\(\delta\) = \(\delta_{ac}\)). Figure 7: Lateral variations through (**a**) the point target at (\(x\),\(z\)) = (9.1 mm, 37.6 mm), and (**b,c**) two anechoic cysts in experimental cyst images. DMAS. LOCw-CMSB improves the CR by 27.7% and 34.4% compared with CMSB (\(\delta\) = 0.7) and CMSB (\(\delta\) = 1.3), respectively. In addition, the gCNR and sSNR of LOCw-CMSB are almost equal to that of CMSB (\(\delta\) = 1.3) at the shallower depth, whereas they are 0.07 and 0.17 lower than that of (\(\delta\) = 1.3) in the deep region. CMSB (\(\delta\) = \(\delta_{ac}\)) obtains improvements of 2.1% and 42.7% in gCNR and sSNR over that of CMSB (\(\delta\) = 1.3), while the CR decreases by 2.5%.