1. A method for retrospectively correcting data prior to image reconstruction using an imaging system having a Z-axis extending longitudinally therethrough, said method comprising: acquiring a first sinogram of a first slice of an object at a first axial field of view at a first location with respect to the Z-axis; acquiring a second sinogram of the first slice of the object at a second axial field of view different than the first axial field of view, the second axial field of view at a second location with respect to the Z-axis, the second location different than the first location; 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 at least one determined boundary; assuming a linear change in the shift with respect to a slice location of the first slice at the second axial field of view; deducing an offset for the first slice at the second axial field of view in the second sinogram as a function of the measured shift and the assumed linear change; and generating a corrected image using the deduced offset for the first slice at the second axial field of view in the second sinogram to make a back projector and a forward projector, knowledgeable of an intended center for a projection.