For a SMV projection of the sinus with a horizontal beam, the CR is directed through which structure?

• A. Sella turcica
• B. Perpendicular to the IOML
• C. Frontal bone
• D. Dens

Answer: (A)

In this view, you’re imaging the paranasal sinuses from below, so the central ray is aimed to pass through a midline base structure to place the sphenoid and ethmoid sinuses in the field without being overlapped by the jaw or other bones. The sella turcica is the key midline landmark at the skull base that aligns with the sphenoid sinus region, so directing the beam through it ensures the radiograph nicely shows the sphenoid (and nearby ethmoid) sinuses.

Frontal bone is Too anterior to accurately center the sphenoid/ethmoid area, the dens pertains to the cervical spine and isn’t the target in this projection, and while saying the beam is perpendicular to a line (like IOML) describes technique, the specific structure you want the ray to pass through in this view is the sella turcica.