The diaphragm separates the comparatively dense (white) abdominal organs below it, from the relatively less dense (blacker) lung above. Each hemidiaphragm should appear as a rounded, domed structure with a crisp white edge contrasted against the adjacent dark lung.
Half of the diaphragm, the muscle that separates the chest cavity from the abdomen and that serves as the main muscle of respiration. Both hemidiaphragms are visible on X-ray studies from the front or back.
The right hemidiaphragm is protected by the liver and is stronger than the left. The left hemidiaphragm is more often subject to rupture and hernia than the right. This may also reflect weaknesses at the points of embryologic fusion of the left hemidiaphragm.
The right hemidiaphragm is usually a little higher than the left, to accommodate the liver.
Very often you will see air in the stomach below the left
hemidiaphragm, with the appearance of a dark (less dense) bubble.
It is important to be aware that the lowest portion of the lungs,
which lie in the posterior costophrenic recesses, lie below the level
of the contours of the hemidiaphragms, and occasionally the
stomach bubble forms a window through which this part of the lung