(a, b) Line profiles along the dotted line in Fig. 5 and (c, d) grey-level value histograms for the region delimited by the dashed square in Fig. 5. Black: original phantom; green and red: reconstructions obtained with FBP and gridrec, respectively. For the reconstruction, different filters have been used: Lanczos (a, c) and Parzen (b, d). The size of the original phantom used and the reconstructed images is 2048 × 2048 pixels.