title: Orthogonal Matrix Retrieval In Cryo-Electron Microscopy.
abstract: In single particle reconstruction (SPR) from cryo-electron microscopy (EM), the 3D structure of a molecule needs to be determined from its 2D projection images taken at unknown viewing directions. Zvi Kam showed already in 1980 that the autocorrelation function of the 3D molecule over the rotation group SO(3) can be estimated from 2D projection images whose viewing directions are uniformly distributed over the sphere. The autocorrelation function determines the expansion coefficients of the 3D molecule in spherical harmonics up to an orthogonal matrix of size (2l+ 1) × (2l+ 1) for eachl= 0,1,2,…. In this paper we show how techniques for solving the phase retrieval problem in X-ray crystallography can be modified for the cryo-EM setup for retrieving the missing orthogonal matrices. Specifically, we present two new approaches that we termOrthogonal ExtensionandOrthogonal Replacement, in which the main algorithmic components are the singular value decomposition and semidefinite programming. We demonstrate the utility of these approaches through numerical experiments on simulated data.
authors.affiliation: Princeton University, Program in Applied and Computational Mathematics, Princeton NJ, USA.
authors.forename: Tejal
authors.initials: T
authors.lastname: Bhamre
authors.affiliation: Princeton University, Program in Applied and Computational Mathematics, Princeton NJ, USA.
authors.forename: Teng
authors.initials: T
authors.lastname: Zhang
authors.affiliation: Princeton University, Program in Applied and Computational Mathematics, Princeton NJ, USA.
authors.forename: Amit
authors.initials: A
authors.lastname: Singer
keywords: 3D reconstruction; Cryo-electron microscopy; ab-initio modelling; autocorrelation; convex relaxation; polar decomposition; semidefinite programming; single particle analysis; spherical harmonics