American Society of Radiologic Technologist (ASRT) Practice Exam

Where does the central ray enter during an axial plantodorsal projection of the calcaneus?

1. Head of the third metatarsal

2. Tuberosity of the calcaneus

3. Base of the third metatarsal

4. Third metatarsophalangeal joint

The correct answer is: Base of the third metatarsal

In an axial plantodorsal projection of the calcaneus, the central ray is directed at the base of the third metatarsal. This specific entry point is crucial as it centers the image on the calcaneus while minimizing distortion and ensuring that the entire structure is well visualized in the radiographic image. The 40-degree cephalic angle is applied to the central ray in this projection, which further aids in accurately depicting the anatomy of the heel and surrounding structures. Choosing the base of the third metatarsal allows for proper alignment and orientation of the foot during the imaging process, which is essential for obtaining diagnostic-quality images. This positioning technique also assists in reducing superimposition of other bones in the foot, providing a clearer view of the calcaneus itself.