Influence of additional filter on image quality and radiation dose in chest digital radiography

Objective: To investigate the influence of additional filter on image quality and radiation dose in chest digital radiography (DR). Methods: The adult chest phantom was exposed under the different additional filter by 0, 1.0 mm Al, 1.0 mm Al + 0.1 mm Cu, 1.0 mm Al + 0.2 mm Cu while the kV was 110 kV and the AEC parameter selection were -4, -2, 0, 2, and 4 respectively. Image quality was evaluated by the relative noise and the contrast-to-noise ratio (CNR). The radiation dose was evaluated by the entrance skin dose (ESD) and the effective dose. Linear regression analysis was used to analyze the relationship between the ESD and the effective dose, and the correlation between the image quality and the effective dose was analyzed by Pearson correlation analysis. Results: The ESD were (0.023 ± 0.004), (0.034 ± 0.007), (0.045 ± 0.009), (0.056 ± 0.010), (0.067 ± 0.012) mGy and the effective dose were (6.15 ± 0.09) × 10^-3, (9.02±0.15) × 10^-3, (11.94 ± 0.16) × 10^-3, (14.89 ± 0.09) × 10^-3, (17.80 ± 0.12) × 10^-3 mSv when the AEC parameter selection were -4, -2, 0, 2, and 4 respectively. The effective dose was linearly positively correlated with the ESD and the regression coefficient were (r = 1.000, P < 0.01) under different additional filter. The ESD decreased with the additional filter increased under the same AEC, and the maximum could be reduced by 34%. The relative noise was decreased with the effective dose increased and there was a negative correlation between the two and the Pearson correlation coefficient were (r = -0.970, -0.966, -0.971, -0.971; P < 0.01) under different additional filter. The CNR was increased with more effective dose and there was a positive correlation between the two and the Pearson correlation coefficient were (r = 0.952, 0.947, 0.908, 0.944; P < 0.05) under different additional filter. The relative noise decreased with the additional filter increased under the same AEC, and the maximum could be decreased by 13%. The CNR values increased with the additional filter under the same AEC, and the maximum could be increased by 4%. Conclusions: The use of additional filter in chest digital radiography can reduce the ESD and improve the quality of the image to some extent, but the effective dose change is not significant. (authors)