1. An examination apparatus for examination of an object of interest, the examination apparatus comprising: an acquisition unit for acquiring a four-dimensional data set of the object of interest; a calculation unit adapted for: selecting a first phase volume and a second phase volume from the four-dimensional data set; forward projecting a first voxel of the first phase volume on the basis of a first set of coefficients; forward projecting a second voxel of the second phase volume on the basis of a second set of coefficients; updating the forward projected first voxel on the basis of a third set of update coefficients; updating the forward projected second voxel on the basis of a fourth set of update coefficients; wherein the first voxel and the second voxel have the same spatial coordinates but different phase points.