## 4 Discussion
This result indicates that the fascia can be easily observed by increasing the SNRs of SF and DF, which could be useful for diagnosing diseases such as necrosis that can affect the fascia. For PU, the CNRs of SF-RA and DF-RA increased by 199.88% and 159.75%, respectively, and were statistically different from those of No_PU. The reduction in the signal intensity of the RA was relatively higher than that of the SF and DF in the PU; therefore, the CNR of the PU was higher than that of No_PU. This suggests that the fascia could be clearly observed owing to the increase in the CNRs of SF and DF relative to the RA. These results can promote the observation of the fascia in the image and increase the accuracy and efficiency of facial lesion diagnosis. To image fascia, MRI and a US B-mode scan can be used [37]. Recently, a method using elastography to study fascia function was introduced [38]. However, MRI has various limitations compared to US, such as the high cost and long scan time required. In addition, in the case of elastography using US, tissue elasticity is also provided as a numerical value, so there is no visual difference from existing B-mode images. In this study, the overall signal intensity decreased when the PU was attached; however, the SNR increased in the SF and DF and decreased in the RA. In addition, the signal intensity of RA was significantly lower compared to those of SF and DF, while the CNRs of SF-RA and DF-RA increased significantly. This result proves that when polyurethane is used as an absorber, the SNR and CNR can be increased without a difference in the thickness of the fascia and muscle; thus, the fascia can be observed more clearly in the US image. In most US equipment, parameters such as TGC and gain can be subjectively adjusted according to the operator's visual inspection. In particular, since TGC is divided into several parts depending on the imaging depth, it is difficult to accurately determine the appropriate parameters in detail. This means that a fine adjustment of parameters is limited to the structures localized within each part of the TGC. Unlike TGC, the gain parameter controls the brightness of the entire image and is difficult to fine-tune, so it is difficult to expect the simultaneous changes shown in the SNR and CNR when the PU is attached, as shown in the results of this study. Therefore, US images with the PU attached help distinguish between the fascia and tissues that exist in most body structures, and PU absorber images with improved clarity can be used for a variety of purposes, including identifying tissue boundaries, and calculating the length. This is because the fascia is a connective tissue that surrounds the tissues and organs of the body and serves to distinguish the boundaries between tissues and organs [39; 40]. In particular, the fascia and surrounding tissues in fascial diseases, such as abdominal fascia pain syndrome and plantar fascitits, can be easily distinguished when the PU is used for diagnosis using US images [41; 42]. Moreover, a vascular-enhanced imaging method that uses microbubbles to identify blood vessels and flow using US is currently used [43; 44]. The method using microbubbles can generate the enhanced and differentiated signals when microbubbles attach to blood vessels. However, it requires the invasive injection of microbubbles. Furthermore,microbubble imaging has limitations when applied to infants or patients with diseases, and also has side effects such as headaches, difficulty breathing, and chest pain [45]. However, images obtained using PU instead of microbubbles can also distinguish between blood vessels and tissues more quickly, non-invasively, and without side effects. Because fascia surrounds bones, nerves, and blood vessels, the SNR of fascia around blood vessels with PU may increase [24].