Monte Carlo investigation of phosphor screen optics for use in indirect-conversion detectors

Chang Hwy Lim; Cheol-Soon Shon; Jong Chul Han; Tae Woo Kim; Ho Kyung Kim

doi:10.1117/12.811547

13 March 2009 Monte Carlo investigation of phosphor screen optics for use in indirect-conversion detectors

Chang Hwy Lim, Cheol-Soon Shon, Jong Chul Han, Tae Woo Kim, Ho Kyung Kim

Proceedings Volume 7258, Medical Imaging 2009: Physics of Medical Imaging; 72585H (2009) https://doi.org/10.1117/12.811547
Event: SPIE Medical Imaging, 2009, Lake Buena Vista (Orlando Area), Florida, United States

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.

Citation Download Citation

Chang Hwy Lim, Cheol-Soon Shon, Jong Chul Han, Tae Woo Kim, and Ho Kyung Kim "Monte Carlo investigation of phosphor screen optics for use in indirect-conversion detectors", Proc. SPIE 7258, Medical Imaging 2009: Physics of Medical Imaging, 72585H (13 March 2009); https://doi.org/10.1117/12.811547

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