Abstract
PURPOSE: X-ray detector noise decomposition and normalized noise power spectrum (NNPS) are two metrics proposed in the European Guidelines for the quality control (QC) of digital mammography (DM) systems. We aim to examine the reproducibility of these metrics in longitudinal testing and the relevance of the limiting values in the Guidelines and produce device-specific performance data. APPROACH: Semiannual QC data for 55 DM systems (16 models, 6 manufacturers) were retrieved from our medical physics archive, giving a total of 455 QC tests covering a period of 5 years (10 tests). Average values of the detector response function fit coefficients, the electronic, quantum and structure noise coefficients, and the NNPS data were analyzed across DM models and longitudinally for a given device. The fraction of quantum noise at the clinical detector air kerma ( DAK50 mm ) level was determined, along with the longitudinal change in NNPS. RESULTS: Coefficient of variation for the NNPS at 2.0 mm-1 was 0.04, averaged over all systems. Quantum noise evaluated at DAK50 mm was the largest noise fraction for all devices studied, ranging from 61.2% to 98.2%. Electronic noise was generally lower for the latest X-ray detectors. Consequently, the fraction of quantum noise at DAK50 mm has improved from 6.2% to 28.0% and corresponds to a broader quantum noise-limited range. CONCLUSION: The evaluated noise metrics were reproducible, identified changes in X-ray detector performance, and have a useful role to play in QC testing. The average values have application as reference performance data.