Investigation of the screen optics of thick CsI(Tl) detectors

Adrian Howansky; Boyu Peng; Katsuhiko Suzuki; Masanori Yamashita; A. R. Lubinsky; Wei Zhao

doi:10.1117/12.2082101

18 March 2015 Investigation of the screen optics of thick CsI(Tl) detectors

Adrian Howansky, Boyu Peng, Katsuhiko Suzuki, Masanori Yamashita, A. R. Lubinsky, Wei Zhao

Author Affiliations +

Proceedings Volume 9412, Medical Imaging 2015: Physics of Medical Imaging; 94120G (2015) https://doi.org/10.1117/12.2082101
Event: SPIE Medical Imaging, 2015, Orlando, Florida, United States

Abstract

Flat panel imagers (FPI) are becoming the dominant detector technology for digital x-ray imaging. In indirect FPI, the scintillator that provides the highest image quality is Thallium (Tl) doped Cesium Iodide (CsI) with columnar structure. The maximum CsI thickness used in existing FPI is ~600 microns, due to concerns of loss in spatial resolution and light output with further increase in thickness. The goal of the present work is to investigate the screen-optics for CsI with thicknesses much larger than that used in existing FPI, so that the knowledge can be used to improve imaging performance in dose sensitive and higher energy applications, such as cone-beam CT (CBCT). Columnar CsI(Tl) scintillators up to 1 mm in thickness with different screen-optical design were investigated experimentally. Pulse height spectra (PHS) were measured to determine the Swank factor at x-ray energies between 25 and 75 keV, and to derive depth-dependent light escape efficiency i.e. gain. Detector presampling MTF, NPS and DQE were measured using a high-resolution CMOS optical sensor. Optical Monte Carlo simulation was performed to estimate optical parameters for each screen design and derive depth-dependent gain and MTF, from which overall MTF and DQE were calculated and compared with measured results. The depth-dependent imaging performance parameters were then used in a cascaded linear system model (CLSM) to investigate detector performance under screen- and sensor-side irradiation conditions. The methodology developed for understanding the optics of thick CsI(Tl) will lead to detector optimization in CBCT.

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Adrian Howansky, Boyu Peng, Katsuhiko Suzuki, Masanori Yamashita, A. R. Lubinsky, and Wei Zhao "Investigation of the screen optics of thick CsI(Tl) detectors", Proc. SPIE 9412, Medical Imaging 2015: Physics of Medical Imaging, 94120G (18 March 2015); https://doi.org/10.1117/12.2082101

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