Getting to grips with quantitative image quality measurements for QA of digital mammography (DM) systems

Getting to grips with quantitative image quality measurements for QA of digital mammography (DM) systems Current European Guidelines for the quality assurance of digital mammography systems recommend and outline methods for the quantitative assessment of image quality (IQ). Recommended metrics include the pre-sampled modulation transfer function (MTF), normalized noise power spectrum (NNPS) and the detective quantum efficiency (DQE). The methods described are well established and have been successfully applied to the evaluation of digital mammography systems for QA purposes. At BreastCheck, we have substantial experience in the use of subjective and semi-quantitative test objects such as the CDMAM contrast-detail test object. As an adjunct to these methods, we have integrated quantitative methods to the routine QA programme. We describe the implementation of quantitative image quality metrics and examine the stability of these parameters over time, the ease with which they might be included in a routine QA programme and discuss some of the problems encountered during the implementation. We have demonstrated good comparison between the MTF values obtained from the QA surveys performed on BreastCheck DM systems with results for similar systems published in the literature. We have also found the long-term reproducibility of MTF, NNPS and DQE measurements values (COV∼3%–5%) are as good as quoted in the literature. We expect that the stability of these IQ measurements will facilitate more accurate monitoring of changes in imaging system performance than can be currently achieved using subjective image quality parameters. Consequently, deteriorating IQ performance may be flagged earlier.