Computing the 3-D structure of viruses from electron microscope images

The 3D reconstruction of the electron scattering intensity of a virus from cryo electron microscopy is essentially a 3D tomography problem in which the orientation of the 2D projections is unknown. Many biological problems concern mixtures of different types of virus particles or mixtures of different maturation states of the same type of virus particle. For a variety of reasons, especially low SNR, it can be very challenging to label the type or state shown in an individual image. Algorithms capable of computing multiple reconstructions, one for each type or state, based on images which are not labeled according to type or state, are described and demonstrated on experimental images.