CAMRT Radiography Practice Exam

Where is the central ray directed for an AP, bilateral projection of the posterior ribs below the diaphragm?

1. At the level of the xiphoid tip

2. Through the mid-abdomen

3. Between the xiphoid tip and the lower rib cage

4. Anteroposteriorly at the belly button

The correct answer is: Between the xiphoid tip and the lower rib cage

For an anteroposterior (AP) bilateral projection of the posterior ribs below the diaphragm, the central ray is directed to a location that adequately captures the anatomy of interest. The posterior ribs below the diaphragm correspond to the lower portions of the rib cage, specifically targeting the area that includes the lower ribs and the mid-abdomen region. Directing the central ray between the xiphoid tip and the lower rib cage is optimal because this area is where the ribs transition as they curve downwards, allowing for a comprehensive view of the ribs while minimizing distortion. The xiphoid process serves as a landmark for locating this region, and centering the beam here ensures that both sets of ribs are included in the radiographic image, which is critical for diagnostic purposes. The other options suggest central ray placements that do not adequately capture the entirety of the ribs below the diaphragm or would lead to underexposure or overexposure of the ribs, resulting in incomplete diagnostic images. By focusing on the area between the xiphoid tip and the lower rib cage, the central ray placement is most effective for this projection.