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Description
A photon-counting detector (PCD) typically consists of a top sensor layer and a bottom electronics layer arranged in tandem. The sensor layer detects an incident x-ray photon and converts it into charge carriers, the number of which is proportional to the deposited energy. The bottom application-specific integrated circuit (ASIC) senses the resulting charge drift as a current, converts it into a voltage pulse, and counts photon-interaction events based on the pulse height [1]. The two pixelated layers are electrically coupled using flip-chip bonding.
The realization of a monolithic large-area PCD is challenging owing to several factors, including the physical and electrical uniformity of the sensor material and the precise alignment required for pixel-wise bonding. Consequently, tiling small modular PCD units into strip- or area-type configurations is a common approach for large-area implementations [2].
Pixelated detectors inherently exhibit spatial non-uniformity in signal and noise characteristics due to variations in the sensor or converter material (see Fig. 1(a)). The readout electronics further contribute to this non-uniformity, which is exacerbated in modular PCD configurations.
Unlike energy-integrating detectors, which generate signals by integrating x-ray fluence over a given frame time, PCDs count individual photons. Therefore, temporal stability in counting performance is essential (see Fig. 1(b)). Both spatial non-uniformity and temporal instability can degrade image quality, making appropriate correction essential for reliable operation (see Fig. 1(c)). However, quantitative analyses of image quality before and after such corrections remain limited.
In this study, we investigate the effects of spatial and temporal variations in signal on PCD image quality. The noise-power spectrum (NPS) and detective quantum efficiency (DQE) are employed as image-quality metrics. We also describe detrending approaches for correcting spatial and temporal variations. The image quality of a commercial PCD is evaluated before and after applying these corrections. This study provides insights into improving the reliability and performance of PCD systems.
Acknowledgments
This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (RS-2024-00340520).
References
[1] R. Ballabriga, M. Campbell, and X. Llopart, “An introduction to the Medipix family ASICs,” Radiat. Meas., vol. 136, p. 106271, 2020.
[2] J. Lee, S. Yoo, S. Oh, S. Park, C. H. Lim, J. W. Park, J. Tanguay, and H. K. Kim, “Analysis of the detective quantum efficiency of a dual-energy photon-counting x-ray detector,” NDTE Int., vol. 155, p. 103397, 2025.