1. A computer-implemented method of reconstructing an image object for a measured object in object space from image data in data space during a reconstruction process, the method comprising causing a computer to execute instructions for: separating the object space into at least two zones using data from a first modality representing anatomical information; providing at least two zonal image objects using data from a second modality different than the first modality, each of the zonal image objects defined by a respective one of the at least two zones; reconstructing the image object using a data model derived from separately forward projecting the data from the second modality as each of the zonal image objects into data space, combining results of the separate forward projecting, and back-projecting the data of the second modality from the combined results; and outputting the image object.