A study for the optimization of tube voltage and filter in digital mammography / 中华放射学杂志

ABSTRACT

Objective To investigate the image quality and average glandular dose from different breast compression thickness, and to provide recommendations for filtration material and tube voltage in digital mammography. Methods The CDMAM phantom of 2 to 7 cm thickness were exposed by manual exposure modes(proper mAs, 21 to 39 kVp range) using Mo/Mo and Mo/Rh anode/filer combinations at full-field digital mammography. The image quality figure (IQF), contrast to noise ratio (CNR), figure of merit (FOM) and the average glandular dose (AGD) were obtained from images. The optimum filtration and kVp for each breast thickness were found from the calculated FOMs. And the paired sample rank sum test was used to analyze the difference of AGD, CNR, IQF and FOM for Mo and Rh filters. Results For both Mo and Rh as used filter, under the compression of 2 to 7 cm thickness and the fixed mAs, with the increasing of tube voltage, AGD, CNR and IQF will gradually increase as followingAGD had the significant increasing while CNR and IQF gradually increasing to balance. Under different compression thickness, the AGD for Mo and Rh were statistically different (P<0.05). When the compression thickness were 2 and 3 cm, CNR for Mo was higher than Rh, with the statistically significant difference (P<0.05) while the IQF for Mo and Rh with no statistical significance (P>0.05). When the compression thickness was 4 cm, CNR for Mo and Rh were with no statistical significance (P<0.05) while IQF for Mo was higher than Rh, with statistically significant difference (P<0.05). When the compression thickness were 5 to 7 cm, CNR for Mo was lower than Rh, but only under the thickness of 6 cm with statistically significant difference (P<0.05), while there was no statistical significance (P>0.05) under the thickness of 5 cm and 7 cm; the IQF for Mo and Rh with no statistical significance (P>0.05). The FOM in each thickness for Mo and Rh filtration had statistical significance (P<0.05), and FOMRh>FOMMo. For different compression thickness, the suitable matching of tube voltage and filter material were Rh filtration, 2 cm and 27 kVp, 3 cm and 29 kVp, 4 cm and 29 kVp, 5 cm and 30 kVp, 6 cm and 31 kVp, 7 cm and 32 kVp. Conclusion Considering both image quality and radiation dose, Rh filtration is the optimum selection material and there is a corresponding optimal energy response in all kinds of thickness.