Final answer:
For the PA oblique projection of the sternum, the patient should be positioned with a slight rotation of 15-20 degrees towards the left from the PA position, which separates the sternum from other structures in the thoracic area for a clear image.
Step-by-step explanation:
The proper patient position for the PA oblique projection of the sternum should ensure that the sternum is as lateral to the spine as possible to avoid superimposition. Given the anatomical structure of the sternum, which consists of the manubrium, body, and xiphoid process, and considering the importance of the sternal angle (junction line between manubrium and body of the sternum and the site for attachment of the second rib to the sternum), a specific position for imaging is required. The patient should be rotated 15-20 degrees towards the left from the PA position, which means the left shoulder should be moved posteriorly, while the right shoulder is moved anteriorly, so that the sternum is no longer superimposed over the heart and spine in the radiograph. Note that option (b), (c), and (d), do not describe the correct positioning for this particular radiographic examination.