1. A method for reconstructing a 3D image of an object from a set of x-ray 2D projections of the object, the object exhibiting a periodic motion, comprising: acquiring the set of x-ray 2D projections by employing a gated x-ray imaging technique, each projection of the set of 2D projections being acquired at a respective phase within one of a plurality of gating windows associated with the periodic motion and at a respective perspective with respect to the object; reconstructing a 3D reference image of the object by employing a compressed sensing technique based on at least some of the 2D projections within a given gating window being associated with a reference phase of the periodic motion; reconstructing a plurality of 3D intermediate images of the object by employing an algebraic and/or analytic reconstruction technique based on at least some of the 2D projections, wherein each of the 3D intermediate images is reconstructed within each of the gating windows; registering each of the 3D intermediate images with the 3D reference image to obtain a spatial transformation for each of the gating windows between the respective phase and the reference phase; transforming each of the 3D intermediate images to a joint phase of the periodic motion based on the spatial transformation; and combining each of the transformed 3D intermediate images to obtain the 3D image of the object.