Optimization of image quality and average glandular dose in CR mammography

摘要

The concept proposed by EUREF which determines the AGD between upper limit corresponding to the acceptable level of AGD and lower limit corresponding to lower limit of image quality was applied to CR Mammography, and the resulting object thickness tracking and tube voltage tracking were determined. EUREF specifies threshold contrast visibility for a 5 cm of PMMA. In accordance with this definition, the lower limit of CNR for a 5 cm of PMMA was determined by measuring the CNR at the lower limit of AGD where threshold contrast visibility was just acceptable. The obtained lower limit of CNR was then multiplied by the object thickness compensation factor to estimate the lower limits of CNR for all object thicknesses. AGDs are now determined for each lower limit of CNR to obtain thickness tracking and tube voltage tracking characteristics. Although the limited range of examined target/filter combinations and tube voltages should be taken into consideration, these tracking characteristics for constant CNR differ in their profiles from those of a screen-film system with AEC for providing constant optical density. Among our findings, we found that a lower AGD is achieved while maintaining CNR for a thick object when using a combination of target/filter and tube voltage that generates higher X-ray energy compared to the combination given in the EUREF's typical spectra per PMMA thickness (Mo/Rh 32 kV at PMMA 4cm and Rh/Rh 28 kV at PMMA 6 cm, for example). We also found that the thickness tracking characteristics for constant S value behaves similarly to constant CNR under certain conditions of the target/filter combination and tube voltage.