he inverse second look-up table {circumflex over (l)}0 is applied to this result to yield the second modified filtered back-projection density distributions fc0 as f C ⁢ 0 ⁡ ( x ) = l ^ 0 ⁡ ( ∑ i = 0 N ⁢ 0 ND ⁡ ( i , x ) ⁢ l 0 ⁡ ( P ^ ι ⁡ ( u * , v * ) ) P ^ ι ⁡ ( u * , v * ) ⁢ P ^ ι ⁡ ( u * , v * ) ) . 