A cryo Electron Microscopy dataset is composed of tomographic projections of an object (e.g. a macromolecule). The projection orientation information is unknown. The scope of this paper is the tomographic reconstruction of the observed object in the ab-initio case where the volume has to be estimated only from a raw projection dataset. A new approach based on a parametric model of the volume is presented. The description of the model and the search of the parameters are detailed. The accuracy and robustness of the proposed reconstruction method is shown on synthetic and real databases.