Visualization of the abdominal organs depends on the following factors, taken singly or in combination:

• Differences in opacity between one organ and another.
• The amount of fat—retroperitoneal, mesenteric, and omental—present within the abdomen.  Emaciated or very young animals with little abdominal fat show poor contrast.
• The contents of the abdominal organs vary in density and consequently in opacity.  Such contents may help outline the organs, such as air or gas in the stomach, or feces may outline the colon.