For a SMV projection, the midsagittal plane should be:

For a SMV projection, the midsagittal plane should be:

• A. Parallel to the IR
• B. Perpendicular to the IR
• C. 30 degrees oblique to the IR
• D. At 45 degrees to the IR

Answer: (B)

For an SMV projection, the goal is a true, nonrotated view of the skull base and foramen magnum. Positioning the head so the midsagittal plane is perpendicular to the image receptor achieves this symmetry and prevents left-right rotation from distorting the structures. In this setup the infraorbitomeatal line is aligned with the IR, which helps place the foramen magnum and skull base in profile and allows the central ray to pass along the sagittal axis from submentum to vertex. If the midsagittal plane were parallel to the IR or the head tilted obliquely, rotation would distort the projection and obscure important details.

For an SMV projection, the goal is a true, nonrotated view of the skull base and foramen magnum. Positioning the head so the midsagittal plane is perpendicular to the image receptor achieves this symmetry and prevents left-right rotation from distorting the structures. In this setup the infraorbitomeatal line is aligned with the IR, which helps place the foramen magnum and skull base in profile and allows the central ray to pass along the sagittal axis from submentum to vertex. If the midsagittal plane were parallel to the IR or the head tilted obliquely, rotation would distort the projection and obscure important details.