What positioning line is placed perpendicular to the plane of the image receptor for the parietoacanthial projection (Waters method) of the facial bones?

In the parietoacanthial projection, commonly known as the Waters method, the positioning line of focus is the mentomeatal line. This line is defined as the line drawn from the mentum (the chin) to the mid-point of the external auditory meatus (the ear).

For the Waters method, the mentomeatal line needs to be placed perpendicular to the image receptor. This positioning encourages optimal visualization of the facial structures, specifically the maxillary sinuses, and minimizes the distortion of anatomy. The angling of the skull in this manner allows the X-ray beam to pass through the orbits while positioning the facial bones clearly in the resulting image.

In contrast, the other lines mentioned, such as the infraorbitomeatal, orbitomeatal, and condylomeatal lines, are associated with other radiographic positions or projections and do not fulfill the specific requirement of being perpendicular for the Waters method. Understanding the function and alignment of these positioning lines is crucial for obtaining accurate and diagnostic images in radiography.