Analysis of the detective quantum efficiency of a dual-energy photon-counting X-ray detector

Photon-counting detectors (PCDs) are an emerging technology that provide energy-selective images for a single X-ray exposure. For studies considering PCDs for industrial non-destructive inspection, presenting a metric describing the imaging efficiency or performance of PCDs is important. In this study, we describe the imaging performance in terms of the detective quantum efficiency (DQE) and report the results of the DQE analysis for a sample PCD using a representative X-ray spectrum (70 kV and 21-mm Al filtration). The PCD, a mosaic of eight small detector modules, employs two adjustable energy thresholds and possesses a function called an anti-coincidence (AC) operation, which sums charges spread over four pixels into a pixel exhibiting the highest charge signal. The DQE measurements confirmed that, without correction for the signal and noise correlation between the energy bins, the DQE could be incorrectly overestimated. The AC or charge-summing operation effectively suppressed the signal and noise correlations between the energy bins, enhanced the modulation-transfer functions and removed the cross-noise-power spectra (cross-NPSs) but increased the normalized NPSs in each energy-bin image, degrading the resulting DQE performance. The performance gap between the measured DQE and theoretical models is discussed. The DQE forms and analysis methodologies presented in this paper will be helpful for researchers seeking to understand PCD-based imaging systems.