A novel “ghost”-free tomographic image reconstruction method applicable to rotary-shadowed replica specimens

Electron tomography by conventional filtered back-projection is often seriously impaired by anisotropic resolution due to unavoidable limitation in specimen tilt-angles. We propose a new approach to overcome the problem for thin film-like replica-type specimens in which internal density is supposed as homogenous and contiguously distributed, by imposing a reasonable constraint of density-existing region in the reconstruction procedure. The objects were approximated as a distribution of binary voxels and the intensity of the projected images being proportional to the thickness along the projection ray. The new reconstruction algorithm consists of initial determination of approximate constraint region by a topographic analysis by stereo-photogrammetry, followed by iterative computation to find the unique solution of simultaneous equations, so that all the intensity distribution in tilt-series images are included within pre-determined voxel arrangement. During a trial run with a new methodology, we realized its significantly advantageous feature that much less number of projection images than conventional back-projection is required to perform the reconstruction of almost equivalent quality. Here, we show the performance of this novel algorithm by 3-D reconstruction of quick-freeze deep-etch replica specimens without any trace of spurious ghosting caused by missing-wedge problems.