Identification of the muscularis mucosa of the gastric wall on endoscopic ultrosound imaging using a scanning acoustic microscope

To identify the muscularis mucosa in the ultrasound image of normal gastric wall, Scanning Acoustic Microscope (SAM) system has been employed to measure the sound speed and the specific acoustic impedance which creates the layer appearance of the gastric wall. Nine stomachs resected were studied by SAM and EUS. The cases were classified into three types depending on their acoustic properties. 1) In cases with no significant difference in the acoustic impedance between the muscularis mucosae (mm) and the lamina mucosa propria (1mp), the mm was not distinguishable from the 1mp by EUS. It was speculated that the mm corresponds to the lower part of the second layer of the five layered appearance of the gastric wall in the endoscopic ultrasound image. 2) When the acoustic impedance in the 1mp was significantly larger than the mm, a strong border echo was formed between the mm and the 1mp, the mm layer was not identified. It was speculated that the mm corresponds to the upper part of the third layer of the five layered appearance of the gastric wall. 3) When the difference in the acoustic impedance between the mm and the 1mp was not large enough to form strong border echo, the mm was visualized as a thin hypoechoic layer between second and third layer.