Clavicles

eled CT: 

labeled CT: 

Explanation

The right and left clavicles are outlined in blue.  They are positioned obliquely for a chest CT scan because the patient's arms are raised overhead.  This rotates the scapulae and lifts the lateral ends of the clavicles from the usual resting position. The patient's arms are overhead for this study because it decreases artifacts in the upper portion of the chest due to excessive bone.  If patients are scanned with their arms at their sides, the course of the beam in the coronal plane must pass through the humeri, scapulae, and spine, and this produces streak artifact.