Where should the central ray be directed for a posteroanterior projection of a small bowel series?

In a posteroanterior (PA) projection of a small bowel series, the central ray is directed about 2 inches above the iliac crest. This positioning is crucial because it centers the radiation beam over the area of interest, which includes the distal regions of the small intestine. Placing the central ray at this level ensures that the entire small bowel can be adequately visualized and assessed for abnormalities or conditions such as obstruction or inflammatory diseases.

Positioning the central ray too high—such as at the level of the diaphragm or the xiphoid process—would risk missing essential lower parts of the small intestine, while centering at the level of the umbilicus may not adequately capture the full length of the small bowel and could lead to incomplete or misleading imaging results. Thus, focusing on the area approximately 2 inches above the iliac crest provides the optimal view needed for a thorough analysis during the small bowel study.