Detective quantum efficiency (DQE) of the Dexela 2923MAM detector according to IEC 62220-1-1:2015

Introduction In recent years, digital X-ray imaging devices such as complementary metal oxide semiconductors (CMOS) are widely used in almost all the imaging field applications. Purpose The purpose of the present study was to determine the Detective Quantum Efficiency (DQE) of the Dexela 2923MAM CMOS detector, following the new IEC 62220-1-1:2015 International Standard. Materials and methods DQE was assessed after the experimental determination of the Modulation Transfer Function (MTF) and the Normalized Noise Power Spectrum (NNPS). The CMOS sensor had a pixel size of 74.8 μm coupled to a 200 μm CsI:Tl screen. The MTF was measured following both the IEC 62220-1:2003 and IEC 62220-1-1:2015 methods, while NNPS was determined by 2D Fourier transforming uniformly exposed images. Both parameters were assessed by irradiation under the RQA-3 beam quality. Results The detector response function was linear for the exposure range under investigation. MTFs calculated following the 62220-1:2003 protocol, were found overestimated for spatial frequencies higher than 2 cycles/mm. DQE values, determined with the IEC 62220-1:2003 method, were also found overestimated (spatial frequencies higher than 2 cycles/mm), due to the influence of both MTF and NNPS. The influence of both additive and multiplicative lag effects were found below 0.005, insuring that lag contributes less than 0.5% of the effective exposure. Conclusion The artificially overestimated MTF values resulting following the 2003 protocol is attributed to the MTF averaging, which also averages noise, that is transferred more efficiently than signal through the imaging chain. Disclosure This work was supported by Grant E.040 from the Research Committee of the University of Patras (Programme K. Karatheodori).