A method for extracting information of a cardiac cycle from projection data is presented. The method provides for acquiring one or more sets of computed tomography (CT) projection data. Further, the method includes analyzing the one or sets of CT projection data to obtain a center of cardiac mass. Also, the method provides for estimating raw motion data representative of the motion of the center of cardiac mass from the one or more sets of CT projection data. In addition, the method includes processing the center of mass through time to extract a motion signal from the raw projection data. Also, the method provides for extracting the periodicity information from the motion signal.