Figure 6b. Normal coronary arteries. (a) On a CT scan, the right coronary artery (RCA) and left coronary artery (LCA) arise from the right (R) and left (L) aortic sinuses, respectively. The origin of the left coronary artery is higher than that of the right coronary artery. (b) CT scan shows how the left coronary artery (LCA) is divided into the left anterior descending artery (LAD) and the left circumflex artery (LCX). The right coronary artery (RCA) is seen in the plane that crosses the atrioventricular groove. CT delineates the proximal portions of the coronary arteries more frequently than the distal portions and the left coronary artery more frequently than the right coronary artery.