Volumetric constraints in 3D tomography applied to electron microscopy

3D electron microscopy aims at the reconstruction of density volumes corresponding to the mass distribution of macromolecules imaged with an electron microscope. There are many factors limiting the resolution achievable when this technique is applied to biomolecules: microscope transfer function, molecule flexibility, lack of projections from certain directions, unknown angular distribution, image noise, etc. In this communication we propose the use of a priori information such as particle symmetry, occupied volume, known surface, density nonnegativity and similarity to a known volume in order to improve the quality of the reconstruction. When a series expansion of the reconstructed volume is done, all these constraints are expressed as a set of equations which the expansion coefficients must satisfy. In this work, this equation set is specified and the effect of each one on the reconstruction of a realistic phantom is explored.