If a patient measures greater than 24 cm from the tabletop to the anterior superior iliac spine (ASIS), how should the central ray be directed for the anteroposterior (AP) projection?

In the anteroposterior (AP) projection of the pelvis, the positioning and the direction of the central ray are crucial for obtaining an accurate image. If the distance from the tabletop to the anterior superior iliac spine (ASIS) measures greater than 24 cm, it indicates that the patient's pelvis is closer to a greater degree of obliquity due to their body habitus.

In such cases, angling the central ray cephalad, or upwards, compensates for the increased distance and helps project the central ray more accurately through the pelvis and toward the midline. This adjustment is necessary to ensure that the radiographic image captures the anatomy adequately without distortion, which could occur if the ray were directed straight at 0 degrees.

The 5 degrees cephalad angle is a standard adjustment made when the patient measures greater than 24 cm, as it optimally aligns the radiation beam with the anatomical structures, making it essential for achieving a correct and diagnostic image. This technique is particularly important in clinical settings to enhance image quality and facilitate accurate assessments of the pelvis and surrounding structures.