In an imaging system (10), a short axial length 4D sinograms are loaded one at a time from a data memory (40). A portion of an image memory (44) that corresponds to a currently reconstructed sinogram subset (1112), is initialized. If a part of the object is already reconstructed, an iterative reconstruction is performed in which the previously reconstructed image (m1) is iteratively improved by using the data from the currently reconstructed overlapping image (m2) to converge on the final image.