Development of a Hybrid Direct-Indirect Active Matrix Flat Panel Imager for Digital Radiography
A Howansky1*, A Mishchenko2, S Leveille2, S Dow1, C Orlik1 J Stavro1, A Goldan1, J Scheuermann3, A R Lubinsky1, W Zhao1, (1) Stony Brook University Department of Radiology, Stony Brook, NY, (2) Analogic Canada Corporation, Saint-Laurent, Quebec, (3) Siemens Healthineers, Malden, MA
Presentations
TU-A-TRACK 2-3 (Tuesday, 7/27/2021) 10:30 AM - 11:30 AM [Eastern Time (GMT-4)]
Purpose: Recent work has proposed “hybrid” direct-indirect active matrix flat panel imagers (AMFPIs) for x-ray imaging. Hybrid AMFPIs comprise an amorphous selenium (a-Se) direct AMFPI which is optically coupled to a turbid scintillator, such that a-Se acts as both an x-ray and optical sensor. This work investigates how beam quality and x-ray converter parameters influence the sensitivity, spatial resolution, noise characteristics, and detective quantum efficiency (DQE) of Hybrid AMFPIs.
Methods: A prototype Hybrid AMFPI was constructed by modifying a commercial direct AMFPI (AXS-Screen+v2, 85 μm pitch). Its active matrix was fixed upright to permit imaging in a back-irradiation (BI) geometry, wherein x-rays first expose the detector through the pixel array. Gd2O2S:Tb (GOS) scintillators were coupled to the a-Se to compose different Hybrid AMFPIs. Their x-ray sensitivity, presampling modulation transfer function (MTF), quantum-noise-limited noise power spectrum (NPS), and DQE were measured at RQA5 and RQA9 beam qualities using conventional methods. Phantom imaging experiments were performed to evaluate differences in their imaging characteristics.
Results: Hybrid configurations had greater sensitivity than the direct AMFPI alone; the largest improvement was observed at RQA9 with the thickest GOS due to the increased x-ray quantum efficiency provided by scintillator. Hybrid MTFs were between the direct AMFPI and scintillator MTFs across all configurations and beam qualities. Hybrid NPS featured correlated and white noise components, and an overall noise reduction at low spatial frequencies compared to the direct AMFPI NPS. Hybrid DQEs were accordingly enhanced at low frequencies without penalty at higher frequencies. Phantom images demonstrated more favorable tradeoffs in spatial- and low-contrast resolution with Hybrid AMFPIs than with their constituent direct and indirect imaging components.
Conclusion: Hybrid AMFPIs leverage the favorable x-ray imaging characteristics of direct and indirect AMFPIs, which may improve tradeoffs between spatial- and low-contrast resolution in digital radiography.
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