A position of a center detector of a radiation scanner can be determined without shutting down the scanner and/or manually positioning a phantom in the scanning field of the scanner. A phantom, comprising a target, is scanned to create an axial image of the phantom. The target is masked in the axial image, producing a masked axial image of the phantom. The masked axial image is reprojected in projection space, and the axial reprojection is compared to an axial projection or a rebinned axial projection of the phantom that was used to create the axial image. A target axial projection of data related to the masked target, created from the comparison of the axial projection or the rebinned axial projection and the axial reprojection, is used to determine the position of the center detector.