Kam method for Cryo-EM particle reconstruction

The Cryo-EM 3D particle reconstruction is essential for identifying protein and uncover the biological mechanism of the macro-molecules. In this paper, we use Kam method for reconstruction. Kam method is \textit{ab-initio}, and it assumes that the projection angles of the particle are uniformly distributed. Based on the data covariance matrix, we compute the radial frequency component of the matrix. The particle density function can be obtained by the radial frequency component and the angular frequency basis function. In order to uniquely and accurately identify the radial frequency component, an initial guess of the structure is applied. Experiment shows that Kam method works for low resolution particle reconstruction. Further improvement can be made by including projection angle distribution in covariance matrix, and applying the fast algorithm to enhance computation speed.