Final answer:
In AP and PA projections, 'R' for right and 'L' for left markers are used to correctly orient the anatomical sides of the body, ensuring accurate identification of structures in medical images.
Step-by-step explanation:
Markers used for anteroposterior (AP) and posteroanterior (PA) projections are essential in medical imaging to distinguish the right and left sides of the body. For AP projections, patients face away from the X-ray source and the image receptor is in front of them, capturing the X-rays after they pass through the body. Conversely, in PA projections, patients face the image receptor, so the source is behind them. Markers or labels indicating 'R' for right and 'L' for left are placed on the images to maintain correct anatomical orientation. Diagnostically, this practice ensures accurate identification of body structures and any potential abnormalities such as pulmonary infiltrates, which can be seen as white or lighter areas on an X-ray.