section A:

-at the level sternal angle with 2nd rib.

-in this sequence:2,3,4 and 5th ribs from anteror to posterior.

section B:

-In this sequence:3,4,5, and 6th ribs.

section C:

-4,5,6 and 7th ribs.

section D:

-5,6,7, and 8th ribs.

The oblique course of the ribs precludes assessing more than a short segment in any given section. One simple technique for determining the specific ribs involved in any detected pathologic process begins by identifying the first rib. The anterior portion of the first rib lies along the anterior chest wall at approximately the level of the clavicle. Counting posteriorly in the same section, one can usually identify the second and third ribs, and then on sequential images corresponding ribs can be identified (Figure). Similarly, the second costal cartilage can be identified at the level of the sternal angle, and usually the third through sixth ribs identified in the same section . Another method of identifying ribs is to note that the sternal end of the seventh costal cartilage lies in the same axial plane as the proximal xiphoid.