What is the proper central ray (CR) placement for a lateral sacrum radiograph?

For a lateral sacrum radiograph, the proper central ray (CR) placement is essential for obtaining a clear and accurate image of the sacral area. Placing the CR 3.5 inches posterior to the anterior superior iliac spine (ASIS) targets the sacrum correctly, allowing for optimal visualization of this region's anatomy.

The measurement of 3.5 inches posterior strikes a balance that takes into account the varying anatomy and positioning of the patient. This specific placement ensures that the radiographic beam aligns well with the sacrum and avoids overlapping with other structures, such as the abdomen or pelvis, which can obscure the image.

This positioning helps in achieving the necessary projection to capture the entire sacrum without distortion. Therefore, using 3.5 inches as a reference point is consistent with established radiographic techniques and contributes to accurate diagnosis and assessment of sacral pathology.