The barium swallow test is an X-ray examination of the back of the mouth, the throat and the esophagus. The subject swallows a barium sulfate mixture, which clings to the structures to provide contrast for the X-rays, according to Johns Hopkins Medicine.
Some barium swallow tests also make use of fluoroscopy, reports Johns Hopkins Medicine. With fluoroscopy, there is a continuous X-ray beam passing through the neck as the patient swallows the barium. This allows the technician to create an X-ray movie of the fluid as it passes through the throat. The barium swallow test is useful in the diagnosis of tumors, cancers, hiatal hernias and gastroesophageal reflux disease (GURD).