Improving the resolution of Cryo-EM single particle analysis

We presented a new 3D refinement method for Cryo-EM single particle analysis which can improve the resolution of final electron density map in this paper. We proposed to enforce both sparsity and smoothness to improve the regularity of electron density map in the refinement process. To achieve this goal, we designed a novel type of real space penalty function and incorporated it into the refinement process. We bridged the backprojection step with local kernel regression, thus enabling us to embed the 3D model in reproducing kernel Hilbert space using specific kernels. We also proposed a first order method to solve the resulting optimization problem and implemented it efficiently with CUDA. We compared the performance of our new method with respect to the traditional method on real datasets using a set of widely used metrics for Cryo-EM model validation. We demonstrated that our method outperforms the traditional method in terms of those metrics. The implementation of our method can be found at https://github.com/alncat/cryoem.