A study for tube current exposure time products and image quality in digital mammography

Objective To investigate the relationship between current-exposure time products (mAs) and image quality in digital mammography. Methods The CDMAM phantom of 2 to 7 cm thickness were exposed by manual exposure modes using Mo-Rh anode-filer combinations. The exposure parameters were set as follows: (2 cm, 27 kVp, 10 to 90 mAs); (3 cm, 29 kVp, 20 to 120 mAs); (4 cm, 29 kVp, 20 to 200 mAs); (5 cm, 30 kVp, 40 to 220 mAs); (6 cm, 31 kVp, 40 to 260 mAs); (7 cm, 32 kVp, 80 to 280 mAs). 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 was found from the calculated FOMs. The optimum mAs for each breast thickness were found from the calculated FOMs and IQFs. And the Pearson correlation analysis was used to analyze the correlations among AGD, CNR and IQF. Results With the increase of mAs, the average glandular dose were linearly increased, and the FOM first increased and then decreased or changed slowly. The AGD, CNR and IQF were significantly correlated when the compression thickness was less than 7 cm (r all>0.87, P<0.05). The optimized exposure parameters were list as follows (2 cm,27 kVp,20 to 30 mAs);(3 cm,29 kVp,30 to 50 mAs); (4 cm,29 kVp,80 to 100 mAs); (5 cm, 30 kVp, 80 to 120 mAs); (6 cm, 31 kVp, 100 to 140 mAs); (7 cm, 32 kVp, 80 to 120 mAs). Conclusion The optimum range of mAs can be confirmed with different breast compression thickness and the setting of automatic exposure parameters should be chosen in clinical practice. Key words: Mammography; Image quality; Radiation dosage