Comparison of average glandular dose and image quality between two different target-filter combinations of full-field digital mammography systems

Abstract

Breast cancer is the leading cancer in Thai women while the cancer of the cervix is the second rank. The mammographic system had been developed for the optimization of the radiation dose and image quality to patient. The purpose of the study is to compare the average glandular dose (AGD), entrance surface air kerma (ESAK) and image quality in terms of contrast to noise ratio (CNR) with breast pathology between two different target-filter combinations of full-field digital mammographic systems (FFDM). The system performance was studied for quality control program. The study involves 441 women undergoing screening mammographic examinations in cranio-caudal (CC) view on both breasts. The AGD and ESAK displayed on the monitor were verified and recorded. The CNR was calculated for both groups with pathology of calcifications (macro-micro) or mass who met the eligible criteria. Results: The AGD was 1.75 mGy for Mo-Mo and 1.43 mGy for W-Rh, the ESAK was 11.24 mGy for Mo-Mo and 5.25 mGy for W-Rh at the compress breast thickness (CBT) of 28-59 mm. When the CBT was 70-91 mm, the AGD was 2.01 mGy for Mo-Rh and 1.86 mGy for W-Ag. The ESAK was 14.77 mGy for Mo-Rh and 8.77 mGy for W-Ag. The AGD was reduced to 18.29% when changed from Mo-Mo to W-Rh and 7.46% when changed from Mo-Rh to W-Ag target filter combinations. The ESAK was reduced to 53.29% when Mo-Mo was changed to W-Rh and 40.62% when Mo-Rh was changed to W-Ag target- filter combinations. The mean CNR for calcification detection from Mo/Mo target/filters was 0.86 ±0.66, the minimal contrast detectable was 0.04, the percent contrast was 9.52±7.35. The mean CNR of W/Rh was 1.05±0.75 minimal contrast detectable was 0.04, the percent contrast was 12.44 ±7.74, the percent contrast minimal detectable was 0.58, higher than Mo/Mo of 0.37. For CBT 70-91 mm, Mo/Rh target, the mean CNR was 1.04±0.69, minimal contrast detectable was 0.21, the percent contrast was 10.49±5.79, the mean CNR of W/Ag is 1.59±1.14 minimal contrast detectable was 0.12 the percent contrast was 16.82 ±10.86. The mean CNR for mass detection from Mo/Mo target/filters was 1.36±1.35 minimal contrast detectable was 0.21, the percent contrast was 10.5±7.75, the mean CNR of W/Rh was 1.06±0.79 minimal contrast detectable was 0.22, the percent contrast was 13.84±8.15. The mean CNR for mass from Mo/Rh target/filters combination was 1.4±1.05, the minimal contrast detectable was 0.15, the percent contrast was 11.68±7.19. There was no patient data for W/Ag target. Discussions and Conclusions: The AGD per view for CC view with grid was less than the dose reference level (DRL) of 3.0 mGy as recommended by the ACR. The CBT for data range 60-69 mm was excluded. Different target-filter combinations affect on AGD significantly for the p- value of less than 0.05. The image quality in terms of CNR for calcification and mass detection between two systems was correlated but not significantly different. The errors in calculating CNR may occur from the oversize of ROI drawing over the lesion especially in mass.