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1 March 2019 Indirect photon-counting x-ray imaging using CMOS Photon Detector (CPD)
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CMOS photon detectors (CPDs) are recently proposed photon sensing devices utilizing the latest CMOS image sensor (CIS) technologies [1]. CPDs are non-electron-multiplying devices, whose pixels have a fully depleted photo diode and have a readout noise of sub electron RMS even at room temperature. Using a 15μm pixel CPD test device coupled to a CsI(Tl) scintillator, we successfully obtained photon-count X-ray images. A Hamamatsu Photonics scintillator with 150μm CsI(Tl) layer coupled to fiber optic plate (FOP) of 3mm thickness is diced in dry condition and directly glued to the sensor surface. X-ray photons are injected from an X-ray tube with accelerating voltage of 30kV and 45kV using W target. Each X-ray photon creates a scintillation light spot in the captured images, where the injected position and photon energy are determined by integrating multiple pixel outputs at that spot. X-ray energy distributions were obtained at both 30kV and 45kV with reasonable differences. Modulated transfer function (MTF) of over 0.7 at 10LP/mm was achieved by mapping injected positions at 30kV. Photon-count images for slanted-edge MTF measurements as well as 10LP/mm of X-ray test chart were achieved. Those photon-count images were compared with conventional energy integrating images obtained with the same sensing device. Both image types confirmed superior resolution with photon-counting. This indirect X-ray photon counting technique using CPD has a potential of getting critical X-ray information for medical applications by achieving accurate injected positions of X-ray photons and their energies simultaneously.
Conference Presentation
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Toshiyuki Nishihara, Hiroyasu Baba, Masao Matsumura, Oichi Kumagai, and Takashi Izawa "Indirect photon-counting x-ray imaging using CMOS Photon Detector (CPD)", Proc. SPIE 10948, Medical Imaging 2019: Physics of Medical Imaging, 109481U (1 March 2019);

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