RESUMO
Objective To investigate the radiation dose to phantoms of thick dense breasts (compression thickness ＞ 65 mm) and the influence of Molybdenum-Rhodium (Mo-Rh) and Wolfram Rhodium (W-Rh)) target-filter combination on image quality in full field digital mammography (FFDM).Methods An aluminium plate was placed on polymethyl methacrylate (PMMA) plates to simulate dense breasts.Two of 68 mm in-depth phantoms were used to simulate photography condition of thick dense breasts with 0.1 and 0.2 mm aluminium plates respectively.The two phantoms were exposed automatically,half-automatically and manually.The parameters were recorded for each exposure including the target-filter(T-F),tube voltage (kV),tube current (mAs),average glandular dose (AGD),entrance surface dose (ESD) and the image quality figure inverse (IQFInv).Pearson correlation and regression was used to analyze the influence of AGD on IQFInv.Paired sample t-test was used to analyze the influence of different target-filters on IQFInv and AGD.Results AGD had a positive correlation with IQFInv (r =0.806-0.953,P ＜ 0.05).For the phantom of 0.1 mm aluminium,when the tube current was fixed at 100 mAs or the tube voltage was fixed at 28 kVp,AGD and IQFInv had statistically significant difference for two target-filters(t =3.162-8.028,P ＜0.05).For the phantom with 0.2 mm aluminium,when the tube current was fixed at 100 mAs under different tube voltage,AGD and IQFInv had statistically significant difference for two target-filters(t =4.768-8.028,P ＜ 0.05);when tube voltage was fixed at 28 kVp under different tube current,AGD had statistically significant difference for two target-filters(t =7.730,P ＜ 0.05),while there was no statistical difference in IQFInv(P ＞ 0.05).In addition,when tube current was 100 mAs,IQFInv had statistically significant difference for two phantoms in W-Rh(t =2.345,P ＜ 0.05).Conclusions W-Rh target-filter combination can achieve lower radiation dose under the guarantee of the image quality compared with Mo-Rh target-filter combination.At the same tube current,W-Rh target-filter combination can provide a better image quality under a relatively high tube voltage.