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13 March 2009 Pixel-structured scintillators for digital x-ray imaging
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Proceedings Volume 7258, Medical Imaging 2009: Physics of Medical Imaging; 72583N (2009)
Event: SPIE Medical Imaging, 2009, Lake Buena Vista (Orlando Area), Florida, United States
We exploit the development of a pixel-structured scintillator that would match the readout pixel array, such as a photodiode array. This combination may become an indirect-conversion detector having high x-ray sensitivity without sacrificing the inherent resolving power defined by the pixel geometry of the photodiodes, because the scintillation material has a relatively high atomic number and density compared with the photoconductors, and the pixel-structured design may provide a band-limited modulation-transfer function (MTF) characteristic even with a thicker scintillator. For the realization of pixel-structured scintillators, two-dimensional (2D) array of pixel-structured wells with a depth of 100μm was prepared by using a deep reactive ion etching (DRIE) process on a silicon wafer. Then, Gd2O2S:Tb phosphor powders with organic binders were filled within the well array by using a sedimentation method. Three different pixel designs of 50, 100 and 200 μm with a wall (or septum) thickness of 10 μm were considered. Each sample size was 20 × 30 mm2 considering intra-oral imaging. The samples were coupled to the CMOS photodiode array with a pixel pitch of 48 μm and the imaging performances were evaluated in terms of MTF, NPS (noise-power spectrum) and DQE (detective quantum efficiency) at intra-oral imaging conditions. From the measurement results, the sensitivities of the samples with 50, 100 and 200 μm pitch designs were about 12, 25 and 41% of that of the reference commercial phosphor screen (MinR-2000). Hence the DQE performances at 0.2 lp/mm were about 3.7, 9.6, 22.7% of the reference screen. According to the Monte Carlo simulations, the lower sensitivity was due to the loss of optical photons in silicon walls. However, the MTF performance was mainly determined by the designed pixel apertures. If we make pixel-structured scintillators with a deeper depth and provide reflectance on walls, much enhanced DQE performance is expected.
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Seung Man Yun, Chang Hwy Lim, Tae Woo Kim, and Ho Kyung Kim "Pixel-structured scintillators for digital x-ray imaging", Proc. SPIE 7258, Medical Imaging 2009: Physics of Medical Imaging, 72583N (13 March 2009);

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