The calcium sign is a finding on chest x-ray that suggests aortic dissection. It is the separation of the intimal calcification from the outer aortic soft tissue border by 10mm. (http://en.wikipedia.org/wiki/Aortic_dissection) This is not an important sign for radiographers given that it is rarely seen.

The arrowed distance represents a normal aortic wall thickness	The arrowed distance represents the aneurysmal wall thickness.