The esophagus is a muscular tube connecting the throat (pharynx) with the stomach. The esophagus is about 8 inches long, and is lined by moist pink tissue called mucosa. The esophagus runs behind the windpipe (trachea) and heart, and in front of the spine. Just before entering the stomach, the esophagus passes through the diaphragm.
The upper esophageal sphincter (UES) is a bundle of muscles at the top of the esophagus. The muscles of the UES are under conscious control, used when breathing, eating, belching, and vomiting. They keep food and secretions from going down the windpipe.
In most cases, CT scan is not used to detect gallstones, but this imaging test does have its uses in the biliary system. First of all, the entire main duct can be seen using CT scan because unlike ultrasound, air in the GI tract does not interfere with CT. High-speed CT with computer-assisted reformatting capabilities allows the radiologist to move quickly through numerous images. The ability of CT to find stones in the common bile duct approximates ultrasound. In general, CT scan is a better test for more complicated problems, although it may be used together with ultrasound.