Response functions of multi-pixel-type CdTe detector: toward development of precise material identification on diagnostic x-ray images by means of photon counting

Hiroaki Hayashi; Takashi Asahara; Natsumi Kimoto; Yuki Kanazawa; Tsutomu Yamakawa; Shuichiro Yamamoto; Masashi Yamasaki; Masahiro Okada

doi:10.1117/12.2251185

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9 March 2017 Response functions of multi-pixel-type CdTe detector: toward development of precise material identification on diagnostic x-ray images by means of photon counting

Hiroaki Hayashi; Takashi Asahara; Natsumi Kimoto; Yuki Kanazawa; Tsutomu Yamakawa; Shuichiro Yamamoto; Masashi Yamasaki; Masahiro Okada

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Proceedings Volume 10132, Medical Imaging 2017: Physics of Medical Imaging; 1013236 (2017) https://doi.org/10.1117/12.2251185
Event: SPIE Medical Imaging, 2017, Orlando, Florida, United States

Abstract

Currently, an X-ray imaging system which can produced information used to identify various materials has been developed based on photon counting. It is important to estimate the response function of the detector in order to accomplish highly accurate material identification. Our aim is to simulate the response function of a CdTe detector using Monte-Carlo simulation; at this time, the transportation of incident and scattered photons and secondary produced electrons were precisely simulated without taking into consideration the charge spread in the collecting process of the produced charges (charge sharing effect). First, we set pixel sizes of 50-500μm, the minimum irradiation fields which produce equilibrium conditions were determined. Then, observed peaks in the response function were analyzed with consideration paid to the interactions between incident X-rays and the detector components, Cd and Te. The secondary produced characteristic X-rays play an important role. Accordingly ratios of full energy peak (FEP), scattering X-rays and penetrating X-rays in the calculated response functions were analyzed. When the pixel size of 200μm was used the scattered X-rays were saturated at equilibrium with relatively small fields and efficiency of FEP was kept at a high value (<50%). Finally, we demonstrated the X-ray spectrum which is folded by the response function. Even if the charge sharing effect is not completely corrected when using the electric circuit, there is a possibility that disturbed portions in the measured X-ray spectra can be corrected by using proper calibration, in which the above considerations are taken into account.

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Hiroaki Hayashi, Takashi Asahara, Natsumi Kimoto, Yuki Kanazawa, Tsutomu Yamakawa, Shuichiro Yamamoto, Masashi Yamasaki, and Masahiro Okada "Response functions of multi-pixel-type CdTe detector: toward development of precise material identification on diagnostic x-ray images by means of photon counting", Proc. SPIE 10132, Medical Imaging 2017: Physics of Medical Imaging, 1013236 (9 March 2017); https://doi.org/10.1117/12.2251185

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