For a parietoacanthial projection of the sinuses (Waters method) performed with a horizontal beam, where does the central ray exit?

• A. Nasion
• B. Acanthion
• C. Inion
• D. Glabella

Answer: (B)

In the Waters (parietoacanthial) projection for sinuses, the central ray is aimed to exit at the acanthion. This positioning places the maxillary sinuses optimally in profile and minimizes superimposition, which is why the CR is directed so that it exits through the acanthion, even when the beam is horizontal. The acanthion is the midline point just below the nasal bones, and it aligns the projection with the sinuses more effectively than other facial landmarks.