EUS is performed with radial or linear echoendoscopes, some of which are equipped with special features, such as color and power Doppler [3, 4], contrast harmonic imaging [5, 6], and others [7, 8]. EUS typically produces high-frequency ultrasound between 5 and 20 MHz, which can generate a high-resolution image in the near field with a limited penetration depth ranging from 1–2 to 5–6 cm, depending on the ultrasound frequency.

In general, gastric EUS is performed with the patient in the left lateral position, usually under conscious sedation with benzodiazepines in conjunction with a central analgesic. Propofol has been used recently and is associated with very low complication rates [9–11]. Radial echoendoscopes generate radial images of 360° and are oriented perpendicular to the shaft axis of the instrument. In contrast, linear echoendoscopes produce images directed parallel to the shaft axis of the endoscope , allowing effective and safe performance of EUS-guided fine-needle aspiration (EUS-FNA) . In our personal experience, radial imaging offers a better view of the gastrointestinal wall and the structures surrounding the stomach, and it provides a complete scan, unlike the linear echoendoscope that requires rotating the scope manually 360 degrees to get a complete view. This is a matter of personal preference, and some endosonographers (especially in the Western Hemisphere) may prefer the linear instrument for initial staging with the idea that any lymph nodes or other lesions that need EUS-FNA can be targeted immediately without changing the scope. EUS with high-frequency ultrasound probes is especially useful for early gastric cancer as opposed to the radial or linear echoendoscopes that are used in imaging advanced gastric cancer. Therefore, the choice of staging method—echoendoscope or miniature probe EUS—may first depend on the estimation of tumor depth (T stage) from findings on upper endoscopy or other imaging modalities [12, 13].

Adherence to the following principles during EUS will help ensure clear images.

The gastric wall typically consists of five distinct layers by EUS using the echoendoscopes with 7.5–12 MHz [14–16]. The first two inner layers with high and low echogenicity represent the interface/superficial mucosa and deep mucosa/muscularis mucosa. The third hyperechoic layer corresponds to the submucosa, the fourth hypoechoic layer to the muscularis propria, and the fifth hyperechoic layer to the serosa, which usually is not easily distinguishable from the surrounding echo-rich tissue. Using higher frequency EUS miniprobes (12 to 20 MHz) and under optimal conditions, up to nine gastric wall layers can be identified. The surrounding organs, vessels, and other structures are important for diagnosis as well as for orientation (e.g., to determine tumor infiltration depth). These organs and other structures include the pancreatic body and tail, parts of the liver (especially the left lobe), parts of the left kidney and spleen, and vessels such as the aorta, vena cava (proximal stomach), celiac trunk, and the splenic and left renal veins. In everyday practice, both the water filling the lumen and balloon inflation methods can be combined for improved imaging.