Experimental investigation of direct–indirect flat-panel imager using tellurium-doped amorphous selenium

Purpose: Active matrix flat panel imagers (AMFPIs) are widely used in digital radiography, but both direct and indirect conversion technologies have limitations. Amorphous selenium (a-Se)-based direct detectors suffer from low X-ray quantum efficiency, whereas indirect detectors experience resolution loss due to optical photon scatter. A direct–indirect “Hybrid” AMFPI, combining both technologies in a single detector, has shown promise in overcoming these issues by incorporating an a-Se layer in contact with a scintillator, functioning as both an X-ray and optical sensor. Approach: We aim to improve the detective quantum efficiency (DQE) of the first Hybrid AMFPI prototype by (1) increasing the a-Se layer thickness and (2) doping a-Se with tellurium (Te) to improve optical quantum efficiency (OQE). A 6.5 × 6.5 cm² prototype imager was fabricated with 700 μm a-Se, a Te-doped a-Se optical sensing layer, and a removable 1000 μm CsI:Tl scintillator. Results: The Hybrid configuration showed a 42% (RQA5) and 91% (RQA9) increase in X-ray sensitivity over the direct AMFPI due to a 10-fold OQE improvement from Te doping. The Hybrid AMFPI achieved a DQE(0) of 0.90 (RQA5) and 0.75 (RQA9). Real-time (30 frames-per-second) temporal performance measurements demonstrated minimal ghosting (<2%) but up to 12% lag, attributed to electron trapping in the Te-doped layer. Conclusions: Hybrid AMFPI is the highest-performing imager for digital radiography applications as quantified by DQE at RQA9 beam quality but is currently limited by image lag. Future research will explore arsenic co-doping to improve electron transport for real-time imaging.