title: Super-sampling SART with ordered subsets.
abstract: In tomography, the quality of the reconstruction is essential because the complete cascade of the subsequent analysis is based on it. To date, weighted back-projection (WBP) has been the most commonly used technique due to its versatility and performance in sub-tomogram averaging. Here we present super-sampling SART that is based on the simultaneous algebraic reconstruction technique. While algebraic reconstruction techniques typically produce better contrast and lately showed a significant improvement in terms of processing speed, sub-tomogram averages derived from those reconstructions were inferior in resolution compared to those derived from WBP data. Super-sampling SART, however, outperforms both in term of contrast and the resolution achieved in sub-tomogram averaging several other tested methods and in particular WBP. The main feature of super-sampling SART, as the name implies, is the super-sampling option - by which parameter-based up-sampling and down-sampling are used to reduce artifacts. In particular, the aliasing that is omnipresent in the reconstruction can be practically eliminated without a significant increase in the computational time. Furthermore, super-sampling SART reaches convergence within a single iteration, making the processing time comparable to WBP, and eliminating the ambiguity of parameter-controlled convergence times. We find that grouping of projections increases the contrast, while when projections are used individually the resolution can be maximized. Using sub-tomogram averaging of ribosomes as a test case, we show that super-sampling SART achieves equal or better sub-tomogram averaging results than WBP, which is of particular importance in cryo-electron tomography.
authors.affiliation: Goethe University Frankfurt, Buchmann Institute for Molecular Life Sciences and Institute for Biophysics, Max-von-Laue Str. 15, 60438 Frankfurt am Main, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Kunz
authors.affiliation: Goethe University Frankfurt, Buchmann Institute for Molecular Life Sciences and Institute for Biophysics, Max-von-Laue Str. 15, 60438 Frankfurt am Main, Germany. Electronic address: achilleas.frangakis@biophysik.org.
authors.forename: Achilleas S
authors.initials: AS
authors.lastname: Frangakis
mesh_terms: D000465:Algorithms; D055032:Electron Microscope Tomography / Q000379:methods*; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D012270:Ribosomes / Q000737:chemistry; D015983:Selection Bias
keywords: Algebraic reconstruction techniques; Reconstruction methods; Sub-tomogram averaging; Weighted backprojection