1. A projector for iterative fully-3D reconstruction of an image by positron emission tomography (PET) using a scanner comprised of a plurality of detector elements comprising: a volume image memory containing a resultant image volume that is initially estimated and stored in an image matrix; a projection matrix, wherein said projection matrix is comprised of planes of projection data collected at each of a plurality of data collection directions and said data collection directions include azimuthal angles of projection rays or lines-of-response that are perpendicular to the axis of symmetry of the scanner between detector elements in a same transaxial plane of the scanner and axial angles of oblique projection rays or lines of response between detector elements in different transaxial planes of the scanner; and a rotator that re-samples said resultant image volume from said volume image memory by rotating the image matrix to a given azimuthal angle of the projection matrix and slanting the columns of the image matrix to each of the axial angles of oblique projection rays or lines-of-response at that given azimuthal angle such that columns of the image matrix align with each of the plurality of data collection directions of the projection matrix, wherein said rotator applies a coarse-depth compression factor to said image matrix such that rows of the image matrix are collapsed onto one another in accordance with the coarse-depth compression factor so depth information of the rotated image matrix is compressed and said image is projected by summing the compressed columns of the image matrix, thereby creating a fully-3D reconstruction of an image by positron emission tomography.