What is the appropriate central ray angulation and entrance point for an AP axial projection of the coccyx?

• A. 15 degrees cephalad entering MSP at a level 2 inches superior to the pubic symphysis
• B. 10 degrees caudad entering MSP at 2 inches superior to pubic symphysis
• C. 15 degrees cephalad entering MSP at pubic symphysis
• D. 10 degrees cephalad entering 2 inches inferior to pubic symphysis

Answer: (B)

For the AP axial view of the coccyx, the goal is to project the coccyx free of overlap with the pelvic bones by aligning the beam with the coccyx’s axis. A small caudad angulation directs the central ray toward the coccyx and helps separate it from the surrounding structures, reducing superimposition. The entrance point is at the midline about 2 inches above the pubic symphysis; this location ensures the beam passes through the coccyx rather than through the lower abdomen and centers the coccyx in the image. Using a 10-degree caudad angle with the CR entering the midline at that level provides a clear axial view of the coccyx by maximizing projection and minimizing distortion. Angles or entry points that are cephalad or located at the symphysis can misproject the coccyx or increase overlapping pelvic structures, making the coccyx harder to visualize.