(a) The three vessels view showing the relationship and size of the pulmonary artery, aorta and superior vena cava (three vessels). The pulmonary artery, to the left, is slightly larger than aorta and the superior vena cava is the smallest and posterior vessel. PA, pulmonary artery; AO, aorta; SVC, superior vena cava; R, right; L, left. (b) The three vessels view showing the aorta and ductus arteriosus located to the left to trachea. The thymus can be visualized in the front of three vessels. PT, pulmonary trunk; LP, left pulmonary artery; RP, right pulmonar artery; AO, aorta; SVC, superior vena cava; T, trachea.