Historical trends in image quality and mean glandular dose in digital mammography

摘要

Purpose: The methods used in the NHS Breast Screening Programme (NHSBSP) evaluation reports have been consistent over the last 15 years and so it is of value to examine the long term trends in image quality and radiation dose. Method: The mean glandular dose (MGD) measured using 45 mm thick polymethyl methacrylate and threshold gold thickness (t_T) measured using a CDMAM phantom were collated from 30 technical NHSBSP evaluations reports of digital radiography (DR) mammography systems and computed radiography (CR) detectors. Results: There was a wide range of MGD measured for the different systems, but on average there was no significant change in MGD over time for DR. The measured t_T for the 0.1 mm detail sizes significantly improved over time for DR. The MGD required for a system to reach the achievable level of t_T (MGD_T) was calculated. This showed that modern DR systems required a lower MGD_T. Theoretically all of the DR systems and one CR detector could have been set up to be at the achievable level or better. The MGD, t_T and MGD_T results for CR detectors were on average worse than for DR. Conclusions: The quality of the DR systems has improved over time, it was also noted that the difference between the worst and the best system has been decreasing. It would appear that generally manufacturers have set up their systems to take advantage of the improved quality of their systems by improving the quality of the images rather than reducing MGD.