In an Endoscopic Ultrasound (EUS), the patient is sedated and a flexible tube with a fiber optic light and camera (endoscope) is passed through the mouth down the esophagus into the stomach and the duodenum (the upper section of the small intestine). 
The procedure is similar to an upper endoscopy exam, but the scope is additionally equipped with ultrasound technology to help assess tissues below the surface of the esophagus, stomach and duodenum.  The ultrasound component uses sound waves to create a picture of the inside of the body and is used to assess possible tumors of the esophagus, stomach, pancreas, gall bladder and liver, and chest cavity tumors. It is also used to evaluate abdominal pain and diseases of the pancreas, such as pancreatitis, and gallbladder, like gallstones and bile duct obstructions.
The combined medical techniques enhance the physician’s ability to accurately stage gastrointestinal tumors and lung cancers up to 90% and help the patient plan treatment options.