A phantom study regarding the formation mechanism of mucosal epithelial echo on intraoral ultrasonography

Objectives: This study is aimed to perform imaging of phantoms to simulate intraoral ultrasound and to investigate the formation mechanism of mucosal epithelial echo. Methods: In this study, we used phantoms, simulated mucosal layer (SML) with thickness of 0.5, 1.0, 3.0 mm and no SML, and an intraoperative small linear probe as ultrasound transducer. Acoustic coupling polymer gel and agar gel were used as the coupling material, and polyvinylidene chloride (PVDC), polyethylene (PE) and polymethylpentene (PMP) plastic wrap were used. The thicknesses of a surface echo and mucosal epithelial echo were measured on B-mode images. Results: A surface echo approximately 0.5 mm thick and a hyperechoic line structure approximately 1.0 mm deep in the 3.0-mm SML, which were presumed to be artifacts, were visualized with all combinations of acoustic coupling material and plastic wrap except with acoustic coupling agar gel and PMP wrap. When using acoustic coupling polymer gel, a hypoechoic line approximately 0.2 mm thick was observed, even when no SML was present. Thickness of the SML appeared to be lesser on ultrasound images than its actual depth, and the most accurate measurement of thickness was obtained using acoustic coupling agar gel together with PMP wrap. Conclusion: When using acoustic coupling polymer gel, artifacts may have prevented accurate visualization over an area that is approximately 0.6-0.7 mm thick. This shows that when intraoral ultrasound is performed by this method, it may not be possible to accurately visualize the mucosal epithelium.