Final answer:
In an AP supine or portable chest projection, at least 10 posterior ribs should be visible above the diaphragm for a proper diagnostic image.
Step-by-step explanation:
The minimum number of posterior ribs that need to be visualized above the diaphragm on an anteroposterior (AP) supine or portable projection of the chest is typically at least 10.
This is essential for a proper diagnostic image in radiologic exams.
Since the thoracic cage is formed by 12 pairs of ribs, anchored posteriorly to the 12 thoracic vertebrae, imaging these ribs confirms that the lower pulmonary fields are included in the radiograph, which is crucial for the evaluation of the lungs and other thoracic contents in a chest exam.