Different "views" (also known as "projections") of the chest can be obtained by changing the relative orientation of the body and the direction of the x-ray beam. The most common views are "posteroanterior", "anteroposterior", and "lateral". In a posteroanterior (PA) view, the x-ray source is positioned so that the x-ray beam enters through the posterior (back) aspect of the chest and exits out of the anterior (front) aspect, where the beam is detected. To obtain this view, the patient stands facing a flat surface behind which is an x-ray detector. A radiation source is positioned behind the patient at a standard distance (most often 6 feet, 1,8m), and the x-ray beam is fired toward the patient.