2015Singer Kam

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T. Bhamre, T. Zhang, A. Singer, ``Orthogonal Matrix Retrieval in Cryo-Electron Microscopy”, 12th IEEE International Symposium on Biomedical Imaging (ISBI 2015). arXiv


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 each l=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 term Orthogonal Extension and Orthogonal 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.


Orthogonal extension, orthogonal replacement, phase retrieval, x-ray crystallography, autocorrelation, semidefinite programming, singular value decomposition



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