Survey of radiation dose, image quality and equipment performance of mammography units in Taiwan

This paper describes the results of national survey of mammography systems in Taiwan during the period of February to December 2008. Purpose of the survey was to help understanding the equipment performance, radiation dose, image quality and current status of quality assurance programs of each mammography facility, which served as references for the new regulation of mammography quality assurance and standards started on July 1, 2008 in Taiwan. The scope of the survey covered all mammography units in Taiwan, which included 214 units at 205 sites. Among them, 127 were screen/film units and 87 were digital units (25 CR). The measurements included sensitometry for the screen/film units, signal-difference-to-noise ratio (SDNR) for the digital units, and phantom scores (using the American College of Radiology (ACR) phantom), radiation output, half-value layer (HVL), and average glandular dose (AGD) for all units. The results showed varied sensitometric curves, with a mean base + fog, mid-density (MD) and density difference (DD) of 0.22 ± 0.02, 1.49 ± 0.19 and 1.67 ± 0.23 respectively. Phantom image total scores for screen / film and digital units were 11.09 ± 1.28 and 12.16 ± 0.91, respectively, and were significantly higher (p<0.001) for digital units. The mean SDNR obtained from digital systems ranged from 1.85 to 1.26, a 38% difference, among vendors. The mean AGD was 1.48 ± 0.47 mGy, with the median and third quartile equaled to 1.53 and 1.75 mGy, respectively. There was no significant difference in AGD between the digital and the screen/film systems, except for the CR systems which exhibited significant higher AGD then the screen/film (p<0.001).