Figure 3b. Transverse electron-beam CT scans. (a) CAC screening was performed at electron-beam CT with the use of conventional EKG triggering (80% R-R interval during the cardiac cycle). A coronary arterial motion artifact was found in the RCA (arrow). (b) The same patient as in a underwent scanning with the use of optimal EKG triggering. Coronary arterial movements were greatly reduced in the RCA (arrow).