An image processing device is proposed and includes a reconstruction unit (51) for reconstruction of a 3D volume image of said object from said first series of X-ray projection images (D), a segmentation unit (52) for segmentation of the vessel tree from said 3D volume image, a forward projection unit (54) for forward projection of the segmented vessel tree onto said first and projection plane (R1, R2), respectively, and a mapping unit (55) for mapping of the image values of pixels of the vessel tree in said second and third, respectively, series of X-ray projection images onto corresponding voxels of said 3D volume image to obtain said time series of 3D volume images showing the blood flow in the vascular tree of the object.