Where does the central ray enter the patient for the upright, PA projection of the chest?

For the upright, posteroanterior (PA) projection of the chest, the central ray enters the patient at the midsagittal plane at the level of the seventh thoracic vertebra (T7). This is the standard location for centering during a PA chest radiograph to ensure optimal visualization of the heart and lungs. By directing the central ray to T7, which is typically located approximately at the level of the inferior border of the scapula, the radiographer can achieve the most uniform and clear images of the thoracic structures, minimizing distortion and ensuring that both the lungs and mediastinum are well represented on the film. The alignment along the midsagittal plane also helps in symmetrically imaging the thoracic cavity, which is essential for diagnostic accuracy.