1. A diagnostic imaging system for imaging at a preselected phase point which occurs in one or more successive cardiac cycles as a subject moves in an examination region, the imaging system comprising: an illumination window, which illuminates each reconstructed voxel of the subject in phase point windows adjacent surroundingly the preselected phase point; a temporal window determining processor or algorithm which determines a temporal window, which includes an integer number N of successive cardiac cycles, in which the phase point windows are entirely included in the illumination window, and truncating the illumination window in accordance with the determined temporal window; a Z-region splitting processor or algorithm which determines first and second regions along an axial direction, the first and second regions alternating with one another; a weighting processor which applies normalized weights to readings for the reconstructed voxels lying in the first and second regions of the temporal window; and a backprojection processor or algorithm for three-dimensionally backprojecting the normalized weighted readings into a volumetric image representation.