Scatter-to-primary ratio and grid performance in contrast-enhanced dual-energy digital mammography using Monte Carlo simulations

Scattered radiation and grid performance were investigated for contrast-enhanced dual-energy mammography (CEDM) using Monte Carlo simulations through analysis of the scatter-to-primary ratio ( S P R ), grid selectivity ( Σ ), Bucky factor ( B F ), and signal-to-noise ratio improvement factor ( K SNR ). These parameters were investigated for different grid designs: a 5:1 linear grid ( G 5 2 D ) and a 4:1 cellular grid ( G 4 2 D ), both employed for 2D mammography, and 5:1 and 11:1 linear grids ( G 5 B T and G 1 1 B T , respectively), both employed for breast tomosynthesis. Different breast thicknesses, compositions, along with direct (aSe) and indirect (CsI) image receptors were investigated. Additionally, different x-ray spectra were also evaluated, for low-energy (LE) imaging, with the W/Rh and W/Ag combinations for tube potentials between 24–40 kV, and for high-energy imaging (HE), with W/Cu, Mo/Cu and W/Ti combinations between 40–49 kV. The results showed that the HE spectra yielded higher S P R values than the LE spectra, regardless of grid usage. The dependence of S P R on the tube potential varied between the LE and HE spectra and the image receptor. For the LE spectra, the G 1 1 B T and G 4 2 D grids exhibited lower S P R values, whereas the 5:1 linear grids exhibited higher values. For the HE spectra, higher S P R values were observed with the G 5 B T and G 4 2 D grids and lower values were observed with the G 1 1 B T grid. The grid selectivity decreased with tube potential and breast thickness. For the LE beam, the selectivity was highest for the G 1 1 B T and G 4 2 D grids, and lowest for the G 5 B T grid. For the HE beam, the selectivity was highest for G 1 1 B T and G 5 B T grids and lowest for the G 5 B T and G 4 2 D grids. The Bucky factor decreased with tube potential, but increased with increasing breast thickness. Higher B F values were observed for the breast tomosynthesis grids than for the 2D imaging grids for both the LE and HE beams. K SNR values increased with tube potential for the LE anode/filter combinations, whereas for the HE combinations, the image receptor influenced this relationship. K SNR values also increased with breast thickness, with the G 4 2 D and G 1 1 B T grids showing higher values for the LE and HE spectra, respectively. Lower K SNR values were observed for the G 5 B T grid for both LE and HE beams. The concurrent analysis of K SNR and B F indicated that, for the LE spectrum, the G 4 2 D cellular grid exhibited better performance, followed by the G 5 2 D , whereas the G 5 B T and G 1 1 B T grids performed similarly. For the HE spectrum, the G 4 2 D and G 5 2 D grids demonstrated comparable and better overall performance, followed by the G 1 1 B T and G 5 B T grids. The results of this study demonstrate that, in CEDM, the properties of scattered radiation and grid performance differ significantly between the low- and high-energy spectra used. • X-ray scatter-to-primary ratio differs between low- and high-energy images. • Without a grid, scatter-to-primary ratio also differs between image receptors. • Grid performance differs between low- and high-energy images. • The 4:1 cellular grid demonstrated superior overall performance for CEDM.