For an AP sacrum radiograph, where is the central ray directed?

For an AP sacrum radiograph, where is the central ray directed?

• A. Midline over the sacrum.
• B. Midline over the pubic symphysis.
• C. Midline over the L5 vertebra.
• D. Midline over the coccyx.

Answer: (A)

Direct the central ray along the midline to hit the center of the sacrum. The sacrum is a midline structure, so aligning the beam with the MSP ensures a centered, undistorted image of the sacral body. In practice this is usually set so the CR enters about 2 inches superior to the pubic symphysis, along the midline, and is perpendicular to the image receptor. Directing the ray to the pubic symphysis, to the L5 level, or to the coccyx would misplace the exposure and fail to center the sacrum properly, leading to distortion or incomplete visibility of the sacral body.

Direct the central ray along the midline to hit the center of the sacrum. The sacrum is a midline structure, so aligning the beam with the MSP ensures a centered, undistorted image of the sacral body. In practice this is usually set so the CR enters about 2 inches superior to the pubic symphysis, along the midline, and is perpendicular to the image receptor. Directing the ray to the pubic symphysis, to the L5 level, or to the coccyx would misplace the exposure and fail to center the sacrum properly, leading to distortion or incomplete visibility of the sacral body.