Rotation on a posteroanterior (PA) chest radiograph is indicated by what?

Rotational positioning on a posteroanterior (PA) chest radiograph can be identified by examining the alignment of anatomical structures. The correct choice highlights that unequal distances between the sternoclavicular joints and the spine indicate rotation.

In a properly positioned PA chest radiograph, the sternoclavicular joints should be equidistant from the midline (the spine). When there is a rotation, one sternoclavicular joint will appear closer to the spine, while the other will be farther away. This asymmetry results from the patient's rotation, which skews the alignment of the thoracic structures.

Accurate positioning is crucial for diagnostic imaging, as rotation can obscure important details and lead to misinterpretation. Thus, recognizing the unequal distances helps to assess whether the patient was appropriately positioned in relation to the x-ray beam.