Endoscopy. Doctor about to perform an endoscopy (gastroscopy) examination of a patient's stomach. This technique involves inserting a flexible fibre-optic viewing tube down into the oesophagus, stomach and sometimes duodenum. At the end of the tube is a light that illuminates the inside of the body. The view from the end of the tube can be seen on the monitor at upper centre. Here, the light is illuminating only the patient's tongue and the plastic guard in her mouth. The technique is used to diagnose the cause of severe upper abdominal pain, or of blood in the vomit or faeces. It is also used to check for stomach ulcers or cancer.