Detective quantum efficiency of a double-layered detector for dual-energy x-ray imaging

A sandwich-like double-layered detector can perform dual-energy imaging (DEI) using a single x-ray exposure without object motion artifacts. The energy separation between measurements obtained from the front and rear-detector layers can be tuned by introducing an x-ray beam-attenuating material between them. However, the design of the interdetector filter significantly influences dose efficiency by altering the number of x-ray photons reaching the rear-detector layer within the sandwich detector. Since the sandwich detector typically incorporates phosphors of differing thicknesses for its two detector layers, it exhibits a unique spatial resolution characteristic in the reconstructed dual energy (DE) images. To comprehensively assess detector performance in terms of design (filter) and operation (reconstruction), we established a framework that describes the dual-energy detective quantum efficiency (DE-DQE) using linear-systems theory. The developed DE-DQE model was validated through comparison with measurements. The agreement between the modulation-transfer functions was reasonable, and the correspondence between noise-power spectra was excellent. This proposed DE-DQE concept is universally applicable to any linearly operating DE system and holds a significant value in enhancing the performance of sandwich detectors or ensuring their optimal operation.