 look-up table l0 to the filtered projection {circumflex over (P)}l at in-plane coordinates (u*,v*) and weighting the result with the back-projection weight D and N yields modified weights of the form 0 ND ⁡ ( i , x ) ⁢ l 0 ⁡ ( P ^ ι ⁡ ( u * , v * ) ) P ^ ι ⁡ ( u * , v * ) . These modified weights weight the filtered projection {circumflex over (P)}l as 