1. An imaging system comprising: a data memory into which an acquired sinogram of projection data of an entire object is loaded; and an object reconstruction means for reconstructing an image representation of the entire object in successive sections, which reconstruction means includes: a means for extracting sinogram subsets each corresponding to a prespecified axial length from the data memory one at a time, the prespecified axial lengths partially overlapping, and a sinogram subset reconstruction means for sequentially reconstructing sinogram subsets into successive regions of a common entire object image.