Which cranial positioning line is perpendicular to the IR when positioning a patient for a parietoacanthial projection of the facial bones, Waters method?

Which cranial positioning line is perpendicular to the IR when positioning a patient for a parietoacanthial projection of the facial bones, Waters method?

• A. Infraorbitomeatal line (IOML)
• B. Mentomeatal line (MML)
• C. Frankfort horizontal
• D. Interpupillary line

Answer: (B)

The line kept perpendicular to the image receptor for a Waters parietoacanthial projection is the mentomeatal line. This orientation places the skull so that the chin-to-ear line is vertical relative to the IR, allowing the central ray to exit at the acanthion and the facial bones to be demonstrated with minimal distortion. The orbitomeatal line, in contrast, is not perpendicular here and the OML forms roughly a 37-degree angle with the IR to achieve the proper projection. The other reference lines shown are not used as the perpendicular to the IR for this view, and they won’t place the anatomy in the correct alignment for the parietoacanthial projection.

The line kept perpendicular to the image receptor for a Waters parietoacanthial projection is the mentomeatal line. This orientation places the skull so that the chin-to-ear line is vertical relative to the IR, allowing the central ray to exit at the acanthion and the facial bones to be demonstrated with minimal distortion. The orbitomeatal line, in contrast, is not perpendicular here and the OML forms roughly a 37-degree angle with the IR to achieve the proper projection. The other reference lines shown are not used as the perpendicular to the IR for this view, and they won’t place the anatomy in the correct alignment for the parietoacanthial projection.