be ingested or otherwise placed within a patient. For
instance, barium sulfate, a common mineral, could
be ground up and swallowed to outline the esophagus,
stomach, and small intestine. Barium sulfate could also
be inserted as an enema to visualize the large intestine.
This practice allowed the viewing of strictures,
blockages, ulcers, cancers, and other defects. But the development
of other radio-opaque liquids, now called contrast
agents, which could be used with the kidneys,
the brain and spinal canal, the circulatory system and
the lungs, took much longer and required far more
complex solutions.