The difference between Chest Posterior Anterior (PA) and Anterior Posterior (AP) radiographs.

2. Figure 1 Radiographs and line diagrams demonstrating the difference between a PA and AP projections

Figure 1 demonstrates what the appearance of an AP & PA radiograph with annotation and corresponding line diagrams. They appear different because of the positioning and magnification of structures like the heart and mediastinum


Figure 1 Radiographs and line diagrams demonstrating the difference between a PA and AP projections For all projections the patient needs to be positioned parallel to the detector so that the median sagittal plane is at right-angles to, and in the midline of, the image receptor. For both projections the scapula should be rotated so they do not obscure the lungfields. The lungs, mediastinum and bony thorax (ribs, spine and clavicles) need to be demonstrated. Some spine detail is visualised through the heart and mediastinum. Symmetry is checked by having the medial ends of the clavicle equidistant from the spinous process.