Figure 6c.  Rib counting at CT with the sternal angle as an anatomic landmark. Sequential axial chest CT scans of the ribs and sternum show identification of the sternal angle (*) with the second costal cartilage and rib (2) followed by the counting of the third, fourth, and fifth ribs (3–5) in numeric order (a). The fifth rib is traced as the reference rib in sequential planes (b–d). Note that the rib moves slightly anterior in the caudal planes. The target rib with the metastatic lesion (arrowhead in d) is identified by counting ribs in numeric order from fifth (5) to fourth (4) in the same axial plane.