Where is the central ray directed for a posteroanterior (PA) projection of the chest?

In a posteroanterior (PA) projection of the chest, the central ray is directed at the level of T7, which corresponds to an approximate location where the mid-scapular line intersects the spine. T7 is clinically significant as this level allows for optimal visualization of thoracic structures, including the lungs, heart, and mediastinum, by centering the radiation beam at the area of maximum lung density.

Ensuring the central ray is directed at T7 helps in achieving uniform exposure and minimizing distortions in the images formed. This positioning is vital for accurate interpretation of radiographic findings, as it ensures that both the anterior and posterior aspects of the thoracic cavity are represented correctly on the x-ray film.