The present invention relates to an imaging system for imaging a region of interest, wherein the imaging system comprises a projection data generation unit including a radiation source (2) and a detection unit (6) for acquiring projection data in different angular directions. The projection generation unit is adapted for acquiring projection data in an acquisition region on the detection unit. The imaging system further comprises a reconstruction unit (12) for reconstructing a first image of the region of interest from the acquired projection data and a forward projection unit (13) for forward projecting through the first image of the region of interest for calculating projection data corresponding to regions on the detection unit outside of the acquisition region. The reconstruction unit (12) is adapted for reconstructing a second image of the region of interest from the acquired projection data and from the calculated projection data.