1. An imaging system for imaging a region of interest, comprising: an illumination unit for generating a cone beam for illuminating the region of interest from different directions, a detection unit for generating detection values from the cone beam after having traversed the region of interest, a grouping unit for grouping detection values from different directions, wherein each group comprises at least one alpha detection value and at least one beta detection value, an alpha determination unit for determining at least one alpha aperture weighting value for the at least one alpha detection value of a group, using at least one position of at least one ray within the aperture, which corresponds to the at least one alpha detection value, wherein the alpha determination unit is adapted for determining the at least one alpha aperture weighting value for the at least one alpha detection value in accordance with the following steps: determining redundancy values which are redundant to the at least one alpha detection value, determining positions of redundancy rays, which correspond to the at least one alpha detection value and the redundancy values, assigning an aperture weighting value to each of the at least one alpha detection value and the redundancy values with respect to the determined positions of the redundancy rays, and normalizing the assigned aperture weighting values, the normalized aperture weighting value assigned to the at least one alpha detection value being the at least one alpha aperture weighting value for the at least one alpha detection value; a beta determination unit for approximately determining at least one beta aperture weighting value for the at least one beta detection value of a group using the at least one alpha aperture weighting value of the group, an aperture weighting unit for aperture weighting the detection values using the determined at least one alpha and at least one beta aperture weighting values, a reconstruction unit for reconstructing the region of interest by backprojecting the weighted detection values, wherein the grouping unit is adapted such that each group comprises at least two alpha detection values and wherein the imaging system is adapted such that the at least two alpha detection values of each group comprise the first and the last detection values with respect to the different directions, and wherein the grouping unit is adapted such that each group comprises at least one beta detection value which is located between the at least two alpha detection values, and wherein the beta determination unit is adapted for determining the at least one beta aperture weighting value of a group by interpolation using the alpha aperture weighting values of the group.