Experimental evaluation of fiber-interspaced antiscatter grids for large patient imaging with digital x-ray systems

Radiographic imaging of large patients is compromised by x-ray scatter. Optimization of digital x-ray imaging systems used for projection radiography requires the use of the best possible antiscatter grid. The performance of antiscatter grids used in conjunction with digital x-ray imaging systems can be characterized through measurement of the signal-to-noise ratio (SNR) improvement factor (K_SNR). The SNR improvement factor of several linear, focused antiscatter grids was determined from measurements of the fundamental primary and scatter transmission fraction measurements of the grids as well as the inherent scatter-to-primary ratio (SPR) of the x-ray beam and scatter phantom. The inherent SPR and scatter transmission fraction was measured using a graduated lead beam stop method. The K_SNR of eight grids with line rates (N) in the range 40 to 80 cm^-1 and ratios (r) in the range 8:1 to 15:1 was measured. All of the grids had fiber interspace material and carbon-fiber covers. The scatter phantom used was Solid Water® with thickness 10 to 50 cm, and a 30 × 30 cm² field of view was used. All measurements were acquired using a 104 kVp x-ray beam. The SPR of the non-grid imaging condition ranged from 2.55 for the 10 cm phantom to 25.9 for the 50 cm phantom. The scatter transmission fractions ranged from a low of 0.083 for the N50 r15 grid to a high of 0.22 for the N40 r8 grid and the primary transmission fractions ranged from a low of 0.69 for the N80 r15 grid to 0.76 for the N40 r8 grid. The SNR improvement factors ranged from 1.2 for the 10 cm phantom and N40 r8 grid to 2.09 for the 50 cm phantom and the best performing N50 r15, N44 r15 and N40 r14 grids.