AP radiograph demonstrating<unk>  of the clavicle A rib<unk>  (indicated by two arrows)<unk>  is a term used in describing radiographs that denotes the appearance of a smooth, homogenous, radiodensity with a well-defined margin that runs parallel with a bony landmark.<unk> s represent soft tissue that overlies the respective bony landmark in profile. They are not seen in every radiograph and can be misinterpreted as pathology.
Companion shadow
Mediastinal shift
Double bubble 
Stenvers projection
Auscultatory gap
Hilum overlay sign
Bio-secure bubble
Ground-glass opacity