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Proceedings Paper

Direct measurement of Lubberts effect in CsI:Tl scintillators using single x-ray photon imaging
Author(s): Adrian Howansky; A. R. Lubinsky; S. K. Ghose; Katsuhiko Suzuki; Wei Zhao
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Paper Abstract

The imaging performance of an indirect flat panel detector (I-FPD) is fundamentally limited by that of its scintillator. The scintillator’s modulation transfer function (MTF) varies as a function of the depth of x-ray interaction in the layer, due to differences in the lateral spread of light before detection by the optical sensor. This variation degrades the spatial frequency-dependent detective quantum efficiency (DQE(f)) of I-FPDs, and is quantified by the Lubberts effect. The depth-dependent MTFs of various scintillators used in I-FPDs have been estimated using Monte Carlo simulations, but have never been measured directly. This work presents the first experimental measurements of the depth-dependent MTF of thallium-doped cesium iodide (CsI) and terbium-doped Gd2O2S (GOS) scintillators with thickness ranging from 200 – 1000 μm. Light bursts from individual x-ray interactions occurring at known, fixed depths within a scintillator are imaged using an ultra-high-sensitivity II-EMCCD (image-intensifier, electron multiplying charge coupled device) camera. X-ray interaction depth in the scintillator is localized using a micro-slit beam of parallel synchrotron radiation (32 keV), and varied by translation in 50 ± 1 µm depth intervals. Fourier analysis of the imaged light bursts is used to deduce the MTF versus x-ray interaction depth z. Measurements of MTF(z,f) are used to calculate presampling MTF(f) with RQA-M3, RQA5 and RQA9 beam qualities and compared with conventional slanted edge measurements. Images of the depth-varying light bursts are used to derive each scintillator’s Lubberts function for a 32 keV beam.

Paper Details

Date Published: 9 March 2017
PDF: 11 pages
Proc. SPIE 10132, Medical Imaging 2017: Physics of Medical Imaging, 1013209 (9 March 2017); doi: 10.1117/12.2255561
Show Author Affiliations
Adrian Howansky, Stony Brook Univ. (United States)
A. R. Lubinsky, Stony Brook Univ. (United States)
S. K. Ghose, Brookhaven National Lab. (United States)
Katsuhiko Suzuki, Hamamatsu Photonics K.K. (Japan)
Wei Zhao, Stony Brook Univ. (United States)

Published in SPIE Proceedings Vol. 10132:
Medical Imaging 2017: Physics of Medical Imaging
Thomas G. Flohr; Joseph Y. Lo; Taly Gilat Schmidt, Editor(s)

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