1. A method for acquiring a 3D image dataset of an image object, comprising: acquiring a plurality of 2D image datasets of the image object at a plurality of rotational positions respectively on a trajectory by an X-ray unit, the X-ray unit comprising an X-ray radiation source and an X-ray radiation detector that can be moved in unison into the plurality of rotational positions along the trajectory about an origin of a coordinate system; acquiring a first 3D image dataset by a filtered backprojection of the 2D image datasets, wherein data value redundancies of the 2D image datasets are mutually incorporated in the first 3D image dataset; acquiring a second 3D image dataset by filtering the 2D image datasets that is antisymmetric in respect of a center of symmetry and by a subsequent backprojection of the filtered 2D image datasets, wherein the data value redundancies of the 2D image datasets are not incorporated in the acquired second 3D image dataset; and calculating an averaged 3D image dataset by averaging the acquired first and second 3D image datasets, wherein the data value redundancies are eliminated in the averaged 3D image, wherein the second 3D image dataset is acquired by: defining an axis in a three-dimensional space by an angle relative to an x-axis of the coordinate system, wherein the axis intersects twice with the trajectory, filtering the 2D image datasets by Hilbert transform with symmetric weightings based on the axis, wherein the symmetric weightings relate to the angle at which the axis stands at one of the plurality of rotational positions relative to the X-ray radiation detector, and subsequently backprojecting the filtered 2D image datasets.