Influences of different tube voltages on the dose and image quality of a full field digital mammography / 中华放射学杂志

ABSTRACT

Objective To evaluate the effect of different tube voltages on the radiation dose and image quality of a full field digital mammography system.Methods Both experiments were performed under manual exposure mode.In one experiment,the tube voltages were kept constant at 25,28 and 31 kVp,and the CIRS 015 phantom was exposed at three target/filter combinations molybdenum/molybdenum (Mo/Mo),molybdenum/rhodium (Mo/Rh),and rhodium/rhodium (Rh/Rh) and at tube current-exposure time products of 32-140mAs.The entrance skin exposure (ESE) and average glandular dose (AGD) were recorded,the signal-to-noise ratio(SNR) and contrast-to-noise ratio (CNR) and figure of merit (FOM) were measured to evaluate the influences of different tube voltages on dose and image quality at same target/filter combination.The univariate of randomized completed block-design was used for statistics.In second experiment,the phantom were exposed using Mo/Rh combination when the tube current-exposure time product was kept constant at 56 mAs,and the tube voltage varied between 23 and 33 kVp in 1-kVp increments.The ESE and AGD were recorded,the SNR,CNR and FOM were measured for plotting the curves against tube voltages.Results At Mo/Mo combination,the AGD,ESE,SNR,CNR and FOM of 25,28 and31 kVp were(1.25 ±0.56) mGy,(6.46±2.86) mGy,71.52±8.37,1.91 ±0.26,3.21 ± 0.68; (1.94 ±0.85) mGy,(9.18±4.07) mGy,144.46 ± 11.31,2.41 ±0.28,3.37 ±0.96 and (3.01 ±1.38) mGy,(12.60±5.59) mGy,128.89 ±15.29,2.47 ±0.31,2.31 ±0.76 respectively; at Mo/Rh combination were (1.23 ±0.55) mGy,(5.26 ±2.33) mGy,67.31 ±4.11,1.82 ±0.19,3.01 ± 0.82; (1.86 ±0.84) mGy,(7.57 ±3.34) mGy,139.54 ± 12.16,2.30 ±0.25,3.23 ±0.92 and (2.81 ±1.24) mGy,(10.48 ±4.62) mGy,127.77 ±15.14,2.59 ±0.31,2.67 ±0.68; and at Rh/Rh were(1.09 ±0.48) mGy,(4.89 ±2.16) mGy,67.46 ±2.23,1.48 ±0.72,3.08 ± 1.69; (1.75 ± 0.78) mGy,(6.88 ±3.03) mGy,137.74 ± 14.65,2.37 ±0.26,3.62 ± 1.07 and (2.59 ± 1.13) mGy,(9.32 ± 4.12) mGy,117.91 ± 19.05,2.51 ± 0.31,2.74 ± 0.84.Both experiments indicated that,for a given target/filter combination,the AGD,ESE and CNR increased,but the ESE/AGD decreased with the tube voltage increasing; The first experiment indicated both SNR and FOM of 28 kVp were higher than that of 25 kVp and 31 kVp; the second experiment showed both SNR and FOM decreased with tube voltages increasing.The differences of AGD、ESE、ESE/AGD、SNR、CNR and FOM among the three tube voltages were significant (F =4.391-528.848,P ＜ 0.05) ; but the difference of CNR between 28 and 31 kVp at Mo/Mo and Rh/Rh had no statistical significance (P ＞ 0.05) ; and the differences of FOM between 25 and 28 kVp at the three target/filter combinations were not statistically significant (P ＞ 0.05).Conclusion For a breast with 4.2 cm thickness and 50％ adipose 50％ glandular composition,different tube voltages have significant effects on the radiation dose and image quality.