The usual sense of ultrasound refers to ultrasound performed through the abdominal wall. Unlike ultrasound endoscopy, transabdominal ultrasound is much less valuable than gastroscopy or CT for the diagnosis of gastric cancer and is not commonly used in the diagnosis of gastric cancer. Ultrasound can detect thickening of the stomach wall, uneven mucosal surface, and also some obstruction and food retention manifestations caused by gastric masses, which are meaningful for diagnosing gastric tumors, but not for determining whether they are benign or malignant. Although some manifestations of the stomach wall can be observed through the abdominal wall, the display is often unclear due to the interference of gas and abdominal wall fat in the gastrointestinal cavity.
Patients with suspected gastric cancer need to fast before undergoing transabdominal ultrasound, and oral contrast is usually required before the exam. However, transabdominal ultrasound and barium meal can interfere with each other because both require a special contrast agent, so they usually cannot be done on the same day.
Transepithelial ultrasound is not very meaningful for the diagnosis and staging of gastric cancer, and it is usually not recommended for those who are suspected of having gastric cancer. (Jingyu Huang, Department of Gastrointestinal Oncology, The First Hospital of China Medical University, contributed to the answer)