For an AP projection of the sacrum, how is the CR directed?

In an anteroposterior (AP) projection of the sacrum, the central ray (CR) is indeed directed with a 15-degree cephalic angle. This technique is applied to position the sacrum properly within the radiographic field, compensating for the natural curvature of the sacrum and ensuring that the structure is adequately visualized without distortion or overlap.

The cephalic angulation helps project the sacrum away from the pubic symphysis and minimizes the distance between the image receptor and the OID (object-to-image distance). This positioning is crucial for enhancing the visibility of the sacral anatomy and providing a clearer diagnostic image.

The use of a 15-degree angle is standard practice in most radiographic protocols for the AP sacrum to achieve the most accurate representation of the sacral anatomy in the final image. This technique optimizes image quality by aligning the sacrum parallel to the film or detector, which is essential for appropriate evaluation of any underlying conditions or injuries.