1. A system for processing images, comprising: an imaging system having a x-ray source and an imager; and a processor configured to obtain a tomosynthesis image of an object for a phase of a first physiological cycle of a patient during a first time period using the imaging system, receive a plurality of reference computed tomography (CT) images that are generated at respective phases of a second physiological cycle of the patient during a second time period, select a CT image from the plurality of reference CT images, wherein the selected CT image has a corresponding phase that best matches with the phase associated with the tomosynthesis image, compare the tomosynthesis image with a subset of the CT image, and determine a position of the object based at least in part on a result of the comparison.