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12 May 2020 Evaluation of a hybrid direct–indirect active matrix flat-panel imager using Monte Carlo simulation
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Purpose: Monte Carlo simulations were used to evaluate the imaging properties of a composite direct–indirect active matrix flat-panel imager (AMFPI) with potentially more favorable tradeoffs between x-ray quantum efficiency and spatial resolution than direct or indirect AMFPIs alone. This configuration, referred to as a hybrid AMFPI, comprises a scintillator that is optically coupled to an a-Se direct AMFPI through a transparent electrode and hole blocking layer, such that a-Se acts as both a direct x-ray converter and an optical sensor.

Approach: GEANT4 was used to simulate x-ray energy deposition, optical transport, and charge signal generation processes in various hybrid AMPFI configurations under RQA5 and RQA9 x-ray beam conditions. The Fujita–Lubberts–Swank method was used to quantify the impact of irradiation geometry, x-ray converter thicknesses, conversion gain of each layer, and x-ray cross talk between layers on detective quantum efficiency (DQE).

Results: Each hybrid configuration had a greater DQE than its direct AMFPI layer alone. The DQE improvement was largest at low spatial frequencies in both front- and back-irradiation (BI) geometries due to increased x-ray quantum efficiency provided by the scintillator. DQE improvements persisted at higher frequencies in BI geometry due to preferential x-ray absorption in a-Se. Matching the x-ray-to-charge conversion gains of a hybrid AMFPI’s direct and indirect detection layers affects its Swank factor and, thus, DQE(0). X-ray cross talk has a negligible impact on the DQE  (  f  )   of hybrid AMFPIs with sufficiently high optical quantum efficiency.

Conclusion: An optimized hybrid AMFPI can achieve greater DQE performance than current direct or indirect AMFPIs.

© 2020 Society of Photo-Optical Instrumentation Engineers (SPIE) 2329-4302/2020/$28.00 © 2020 SPIE
Scott Dow, Adrian F. Howansky, Anthony R. Lubinsky, and Wei Zhao "Evaluation of a hybrid direct–indirect active matrix flat-panel imager using Monte Carlo simulation," Journal of Medical Imaging 7(3), 033501 (12 May 2020).
Received: 27 January 2020; Accepted: 27 April 2020; Published: 12 May 2020

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