An algorithm for parallel 3D Reconstruction of Asymmetric objects from Electron Micrographs

Recclltly we proposed a 3D reconstruction algorithm based upon Fourier analysis using Cartesian coordinates. In this algorithm thc computations to determine the values of the 3D Discrete Fourier Transforms of the density of an asymmetric object could be naturally distributed over the nodes of a parallel system. Now we present an improvement of this algorithm which, for reconstruction at poinls of an N x N x N grid, uses O(NJ) arithmetic operations instead of O(N5). We discuss the accuracy of the algorithm and present comparisons of values computed by a parallel program implementing the algorithm with known solutions. Our results are consistent with the ones produced by a sequential program used for many years for structural biology studies. We report the speedup and the load balancing results for processing cryo-EK data for several viruses. We use a cluster of inexpensive PCS interconnected by a switched Ethernet to carry out the 3D reconstruction. One iteration of the 3D reconstruction for the Bursalia Corella Virus that used to take about -I hours using a sequential program was carried out in less than 3 minutes on 16 nodes using the program based upon our algorithm. The algorithm is gllneral iLJId can be used Cor 3D reconstruction of asymmetric objects Cor applications other than structural biology.