## 4 Discussion  
In the medical field, PU is used as a sterile dressing tool and is also manufactured to be used as a probe cover [32; 33; 34]. However, the PU for probe covers compensates for the entire image by adjusting parameters such as time-gain compensation and/or gain, making it difficult to investigate signal differences that occur locally in the image. On the other hand, PU absorbers can be used as markers for local areas and can complement the limitations of previously used metal absorbers. Therefore, this study investigated the changes in the signal intensity of US images depending on whether a PU was attached to the skin, at which point it could easily observe the RA, SF, and DF of the abdomen. The thicknesses and signal intensities of the RA, SF, and DF with the PU were compared with those corresponding to No_PU. The comparison showed that the thicknesses of the RA, SF, and DF with PU decreased by 4.20%, 5.37%, and 12.50%, respectively; however, the differences were not significant. No significant differences were observed in muscle thickness following the RA measurement protocol used in this study. In addition, in the No_PU image, the signal intensity of the SF and DF was much higher than that of the RA, and the hypoechoic signal appeared even when PU was attached, so there was no significant difference in the thickness of the SF and DF depending on the presence or absence of the absorber. Therefore, PU can be used for diagnostic US images, unlike conventional absorption materials such as aluminum and leather, which generate anechoic shadow owing to shadow artifacts [25; 26]. However, the signal intensities of the RA, SF, DF, and BG with PU decreased by 40.97%, 53.05%, 83.70%, and 87.36%, respectively. This reduction occurs due to interactions between \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & & & **Mean** & **SD** &
\begin{tabular}{c} **Mean Difference** \\ **(No\_PU-PU)** \\ \end{tabular} & **SE** & **t Statistic** & \(p\) \\ \hline \multirow{4}{*}{**CNR**} & \multirow{2}{*}{SF-RA} & No\_PU & 16.70 & 6.92 & \multirow{2}{*}{\(-\)33.40} & \multirow{2}{*}{5.38} & \multirow{2}{*}{\(-\)6.20} & \multirow{2}{*}{\(<\)0.001 *} \\ \cline{2-3} \cline{5-8}  & & PU & 50.10 & 26.38 & & & & \\ \cline{2-3} \cline{5-8}  & & No\_PU & 12.30 & 7.97 & & & & \\ \cline{2-3} \cline{5-8}  & & PU & 32.00 & 22.53 & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Comparison of the CNR for No_PU and PU. Figure 3: SNR and CNR changes in each tissue with PU and No_PU. The SNR and CNR show significant differences with PU when compared to No_PU (\(p<0.05\)). * \(p<0.05\), *** \(p<0.001\). PU and each body tissue, including attenuation and scattering due to differences of Z and/or density of the medium. In the case of a metallic absorber, the signal intensity decreases by nearly 100%, resulting in an anechoic image, but in the case of PU, a non-metallic absorber, a hypoechoic image appears. In particular, the amount of change in the BG signal, which is closely related to SNR and CNR, is mostly reduced, meaning that PU can act as an effective filter [35]. Various filtering methods through computer signal processing are being studied to remove noise, and by applying these filtering methods and PU together, an efficient noise improvement method can be developed [35; 36]. The SNR of the RA with PU decreased by 55.90%, whereas those of the SF and DF increased by 46.41% and 113.80%, respectively, and were statistically different from those with No_PU. In the presence of the PU, all signal intensities in the RA, SF, and DF decreased by 83.70%, 41.03%, and 53.05%, respectively, while the SD of the BG decreased by 71.0%. Thus, the SNRs of SF and DF exhibited a greater increase owing to the greater reduction in the SD of BG. However, the SNR of the RA was reduced because of the substantial reduction in the signal intensity of the RA with the PU.