1. A method for retrospectively correcting data prior to image reconstruction using an imaging system, said method comprising: acquiring a first sinogram of a first slice of an object at a first axial field of view and a second sinogram of the first slice of object at a second axial field of view different than the first axial field of view; determining at least one boundary of the object in the first sinogram and the second sinogram at the first slice; measuring a shift between the first sinogram and the second sinogram using the determined boundaries; and generating a corrected image using the measured shift.