For molecules with non-trivial point group symmetry, the Fourier projection theorem implies that each 2D projection image corresponds to multiple slices, where the number of slices equals the size of the symmetry group. As a consequence, determining the 3D structure requires fewer images for molecules with larger point-group symmetries. Our algorithms for orientation assignment currently support cyclically-symmetric molecules.

Further reading:

G. Pragier, Y. Shkolnisky, A common lines approach for ab-initio modeling of cyclically-symmetric molecules, arxiv preprint.