ABSTRACT
Objective To explore the optimum exposure factors in digital chest radiography.Methods Chest phantom was exposed under auto exposure control model with 73, 90, 125kV and S200,400,800 plus or minor 4 micro-adjust for each sensitivity grade. Meanwhile dose area product (DAP) was recorded and the value of IQFinv was analyzed automatically by Artinis CDRAD Analyzer 1.1. Ten volunteers were exposed with 73 kV, S800 - 2; 90 kV, S800 + 2 and 125 kV, S400 + 2. Two radiologists evaluated and scored image quality. Statistical analysis was performed using one way ANOVA test by SPSS 12. 0. Results ( 1 ) The quality scores of volunteers' images obtained with three combinations of exposure factors were 2. 7 ± 0. 5 for 73 kV group, 2. 9 ± 0. 3 for 90 kV group and 2. 8 ± 0. 4 for 125 kV group. The difference among them was not statistically significant ( F = 0. 587, P ＞ 0. 05 ). Whereas the DAP values were (29. 1 ± 7.9) mGy · cm2 for 73 kV group, ( 30. 5 ± 4. 5 ) mGy ·cm2 for 90 kV group and (40. 4 ±7.6) mGy · cm2 for 125 kV group, with statistically significant difference among them ( F = 9. 803, P ＜0. 01 ). (2) In all three kV conditions, DAP value of phantom declined when sensitivity increased. There was a difference of DAP value by 11％ between two successive sensitivity grades. Under the condition of same sensitivity, DAP value changed with kV in the following order: 73 kV ＞90 kV ＞ 125 kV. (3) The value of IQFinv decreased when sensitivity increased. Under the condition of same sensitivity, IQFinv changed with kV as follow: 73 kV ＞90 kV ＞ 125 kV. Conclusion The combination of exposure factors of 90 kV and S800 + 2-S800 +4 is optimum for digital chest radiography.