Gastroenterologists may perform a number of tests in order to determine the cause of problems in the stomach, intestines, or other digestive organs. Some of these include: Anorectal manometry: Measures the muscle tone in your anus and rectum Capsule endoscopy: A tiny camera in a swallowed pill transmits images of your digestive system Colonoscopy: A flexible tube with a camera inserted through the anus to look at your colon Electrogastrography: Electrodes placed on the skin to measure the electrical and muscle activity of the stomach Endoscopic ultrasound: A tube with a camera and ultrasound probe inserted through the mouth or anus to provide images of the digestive tract Endoscopy: A thin flexible tube with a camera inserted through the mouth or an incision to provide images Enteroscopy: A type of endoscopy using a push enteroscope to visualize the first part of the small intestine Esophageal 24-hour pH study: Measures acid and non-acid reflux in your esophagus via a catheter placed through your nose and down your throat Esophageal manometry: A pressure-sensitive tube inserted through your nose and down your throat to measure the movement and function of your esophagus Esophagogastroduodenoscopy: A fiber-optic endoscope with a camera inserted through your mouth to take images of the upper digestive tract Gastroscopy: An endoscope used to look at the stomach and the first part of the small intestine Sigmoidoscopy: A flexible viewing tube (sigmoidoscopy) inserted through the anus to view the last third of the colon