Final answer:
The recommended angulation to prevent foreshortening of the sacrum on an AP projection is 10 degrees cephalad.
Step-by-step explanation:
The correct angulation to prevent foreshortening of the sacrum on an AP projection is 10 degrees cephalad.
Angling the central ray 10 degrees cephalad (towards the head) allows for a better alignment of the sacrum, reducing the foreshortening effect. This slight angulation helps to visualize the sacrum more accurately and prevents distortion.
For example, if the central ray is angled 10 degrees caudad (towards the feet), the sacrum will appear shorter and compressed on the AP projection, leading to foreshortening and potential misinterpretation.