The application of quantitative data analysis for the assessment of flat panel x-ray detectors in digital radiography as part of a quality assurance programme

Abstract

For this study a methodology, which is based on IPEM report 32 Part VII guidance, has been developed for measuring image quality metrics like system transfer properties, signal to noise ratio, modulation transfer function (MTF), normalized noise power spectrum (NNPS) and detective quantum efficiency (DQE) as part a quality assurance programme for digital detectors used in radiography. We investigate the short and long term consistency of the method, inter-detector variability, and we examine the overall applicability and usefulness in routine quality control (QC) measurements. All measurements were performed at a fixed focus detector distance of 140 cm with 1 mm Cu added filtration and 70 kV. Short and long term consistency of our protocol was assessed with a Philips DigiDiagnost that was equipped with a portable detector (Pixium 5500) and a fixed detector (Pixium 4600). Short term consistency for all metrics assessed was excellent with the standard error between five consecutive measurements to be less than 2%. The long term consistency was also very good with the maximum coefficient of variation (cov) to be about 5% for all parameters assessed. Reproducibility of the method was tested against five groups of identical detectors (GE FlashPad, Samsung, Pixium 4600 and 5500, and Canon CXDI-55C). Maximum cov for the MTF, NNPS and DQE were found to be about 5%, 15% and 8% respectively for all detector groups assessed. Furthermore, we demonstrate that relatively large changes in these quality metrics (>15%) indicate changes in detector performance like image artefacts or miscalibrated detectors. The method described in this paper was found to be repeatable and reproducible. In addition, it was easily applied in routine QC and used to monitor changes in detector performance and compare different x-ray detectors used in radiography.