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Proceedings Paper

Monte Carlo investigation of phosphor screen optics for use in indirect-conversion detectors
Author(s): Chang Hwy Lim; Cheol-Soon Shon; Jong Chul Han; Tae Woo Kim; Ho Kyung Kim
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Paper Abstract

We have investigated the optical properties of Gd2O2S:Tb granular phosphor screens for the use in indirect-conversion detectors by using the Monte Carlo method. For the optical model of the phosphor screen, it was regarded as a weak absorbing medium in which scattering is caused by refraction at boundaries between the phosphor grains and organic binders. For the estimation of the light collection efficiency, we included thin passivation (e.g. SiO2) and Si layers as a photodiode in the Monte Carlo geometry only because the optical photons which escape from the phosphor screen exit and towards the Si layer can contribute to signals. In addition, optical coupling materials (e.g., optical fluids), which are practically used in the indirect-conversion detector, were considered. In the Monte Carlo simulations, various design parameters of the phosphor screen were considered such as the refractive index of an optical coupler and passivation layer, a reflection coefficient at the screen backing, and the thickness of an optical coupler. According to the simulation results, the optical coupler played a great role both in light collection efficiency and point-spread function (PSF). The maximum light collection efficiency was achieved when the refractive index of the optical coupler matched to either that of the phosphor screen or that of the photodiode. Moreover, the matched refractive index provided a lesser light spread in the resulting images. The simulation method and result can provide guidelines for a better design of indirect-conversion detectors based on a photodiode array coupled to a phosphor screen.

Paper Details

Date Published: 13 March 2009
PDF: 8 pages
Proc. SPIE 7258, Medical Imaging 2009: Physics of Medical Imaging, 72585H (13 March 2009); doi: 10.1117/12.811547
Show Author Affiliations
Chang Hwy Lim, Pusan National Univ. (Korea, Republic of)
Cheol-Soon Shon, Vatech Co., Ltd. (Korea, Republic of)
Jong Chul Han, Pusan National Univ. (Korea, Republic of)
Tae Woo Kim, Vatech Co., Ltd. (Korea, Republic of)
Ho Kyung Kim, Pusan National Univ. (Korea, Republic of)


Published in SPIE Proceedings Vol. 7258:
Medical Imaging 2009: Physics of Medical Imaging
Ehsan Samei; Jiang Hsieh, Editor(s)

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