During EUS, your doctor will insert a thin, flexible tube (endoscope) into your mouth and digestive tract. In the tube, a tiny ultrasound device (transducer) generates sound waves that provide a precise picture of the surrounding tissue, including lymph nodes in the chest. The endoscope is then progressively removed. As it is withdrawn, the doctor can see inside the body using the ultrasound images. The doctor may use various techniques to obtain better images. For example, he or she might give you a mild sedative before performing EUS so that you are less likely to move while the procedure is taking place. Or, the doctor may inject a small amount of air into certain locations in your body to produce more vivid blood vessels on the ultrasound image. Once the endoscope has been properly positioned, the doctor will remove any previous stitches or implants and insert the transducer through one of the small incisions into your abdomen. The doctor will scan around the outer edge of the stomach and duodenum (the first part of the small intestine) looking for tumors or other abnormalities. If anything is found, the doctor will describe its location and tell you if it is cancerous. If there is no evidence of disease, the doctor will explain what areas have been scanned and how they appear on an EUS image. EUS is useful for diagnosing tumors located in the pancreas, gallbladder, liver, spleen, intestines, and stomach.