American Registry of Radiologic Technologists (ARRT) Practice Exam

When the central ray (CR) is angled 40° cephalic during the imaging process for the calcaneus, it indicates that the x-ray beam is directed towards the head in an upward manner. This angling is essential for capturing a clear view of the calcaneus.

The plantodorsal projection, which is the correct answer, is typically performed to visualize the calcaneus by directing the beam from the plantar surface (the bottom of the foot) towards the dorsal surface (the top of the foot) at this specific angle. This technique allows for a detailed image of the bone anatomy, highlighting key features such as the subtalar joint and the overall alignment of the calcaneus.

Other projections mentioned, such as the medial-lateral and lateral projections, do not involve a cephalic angle and serve different purposes in diagnosing conditions related to the foot and ankle. The superior-inferior projection, similarly, focuses on a different orientation and does not utilize a cephalic angle to visualize the calcaneus effectively. Therefore, understanding the angle and direction of the x-ray beam is crucial when selecting the proper projection for diagnostic imaging of specific bones, such as the calcaneus.