1. A method for data-based cycle estimation and computed tomography (CT) reconstruction, the method comprising: scanning a patient with a computed tomography (CT) scanner without gating; reconstructing, with a processor, CT images with trigger reference points added for a gated reconstruction, the trigger reference points based on an expected cycle length of a breathing cycle, the images representing each of a plurality of slices at different times; deriving the breathing cycle from the images; binning the images into breathing phases using the breathing cycle; generating a four-dimensional reconstruction of the patient as a function of the binned images for the breathing phases.