During the arms up position, there is high-grade narrowing of the left subclavian artery, as it passes through a gap 2 mm wide between the left clavicle and the superiormost left rib. The first rib articulates with both the sternum and left second rib. There is however good contrast opacification in these subclavian artery and its branches distal to this point of external compression. There are no filling defects to suggest thrombus. On the right, the minimum distance between clavicle and first rib is 7 mm in the arms up position which equals the diameter of the right subclavian artery, and no compression is evident. Unremarkable aortic arch. Innominate and left common carotid artery appear normal.