Where should the central ray (CR) be directed for an AP projection of the abdomen?

• A. At the xiphoid process
• B. At the pubic symphysis
• C. At the iliac crest
• D. At the greater trochanter

Answer: (C)

For an AP projection of the abdomen, the central ray (CR) should be directed at the level of the iliac crest. This positioning is crucial because the iliac crest serves as an anatomical landmark for locating the appropriate area of interest in the abdomen. Positioning the CR at the iliac crest ensures that the entire abdomen, from the diaphragm to the pubic symphysis, is well visualized and included in the radiograph.

Additionally, the iliac crest corresponds to the L4-L5 vertebrae, a central point in the abdominal cavity that helps capture vital structures such as the liver, spleen, kidneys, and bladder in one image. This method maximizes the diagnostic value of the image while allowing for standardization across various patients. This rationale for using the iliac crest further enhances the clarity and effectiveness of an abdominal radiographic examination.