CDMAM in digital mammography: contrast threshold measurements, achievable values and relation with dose

The main goal of this study is to characterise threshold contrast values and average glandular dose (AGD) in mammography examinations, as well as their relationship with acceptable (minimum quality values) and achievable (desirable quality values) values from the fourth edition of the EUREF protocol. Therefore, data from 84 mammography units from six different manufacturers comprising 15 different models were gathered across Portugal during 2020 and 2021. The contrast measurements were obtained with a CDMAM 4.0 phantom. Within the tested units, six failed to comply with the acceptable EUREF values for threshold contrast and 5% achieved all levels of desirable contrast. Only 3% of the units presented values above an achievable AGD level of 2.4 mGy for an equivalent breast thickness of 60 mm. As these acceptable and achievable values are used as a guideline for the setup of dose and image quality of mammography units, the obtained results demonstrate that clinical images are being produced with an AGD much lower than the achievable dose values. As a result, contrast threshold values are close to the minimum quality values, which could result in images with less diagnostic data, compromising the justification of x-ray exams. Results proved that there is a possibility for an increase in AGD to give achievable image standards. Higher levels of radiation dose correlated with better image quality, and consequently higher diagnostic confidence could be consistent with the optimisation principle for radiation protection.