What direction should the central ray be directed for the submentovertex (SMV) projection?

For the submentovertex (SMV) projection, the central ray must be directed perpendicular to the image receptor. This alignment is essential to ensure that the image accurately represents the anatomy of interest, particularly the cranial base and the maxillary sinuses. When the central ray is perpendicular, it provides a uniform projection that minimizes distortion, allowing clearer visualization of the structures.

The SMV projection is specifically used to visualize the zygomatic arches, the mandible, and the area between the orbits, making the accurate positioning of the central ray crucial for optimal diagnostic images. Proper technique with the correct ray direction facilitates better anatomical representation, ensuring that anatomical relationships and abnormalities can be observed effectively.