Speaker
Description
Hybrid pixel X-ray detectors operating in single-photon counting mode provide high spatial resolution, enhanced spectral imaging, and immunity to electronic noise. A common trend is to minimize pixel size, however, it often comes at the expense of spectral fidelity and position resolution due to charge sharing between channels. The spatial resolution can be further improved, though, by analyzing the proportions of charge collected by neighboring pixels. This work focuses on a new digital algorithm that leverages charge sharing to detect event positions with subpixel resolution. Digital algorithms are modeled using the SystemVerilog and verified through simulations.
Summary (500 words)
Hybrid pixel X-ray detectors are multichannel devices consisting of a sensor bonded to readout electronics. Detectors operating in single-photon counting mode, which process each incoming photon individually, offer several advantages over integrating detectors, including high spatial resolution, enhanced spectral imaging, and immunity to electronic noise [1]. Single-photon counting technology has improved substantially in recent years. A common strategy is to minimize pixel size, enabling higher count rates. However, reducing pixel size often comes at the expense of spectral fidelity and position resolution due to increased charge sharing between channels. This charge sharing can lead to false event registration or missed events, resulting in degraded energy and position resolution.
Algorithms designed to mitigate the effects of charge sharing are already implemented on-chip [2]. These typically handle situations where charge is shared among up to four neighboring pixels. However, the spatial resolution of the detector can be further improved, beyond the physical pixel size, by analyzing the proportions of charge collected by more than four neighboring pixels [3], [4].
This work continues the development of the theoretical models presented in [4] and offers an alternative to the existing on-chip solution described in [3]. We focus on implementing a new digital algorithm for pixel photon-counting detectors that leverages charge sharing to detect event positions with subpixel resolution. As an alternative to existing solutions, we evaluate digital algorithms based on either the approximation of the inverse error function or a Gaussian look-up table. The design is modeled using the SystemVerilog hardware description language and verified through both targeted and random simulations. The impact of architectural trade-offs on position reconstruction accuracy and silicon area is assessed. Simulations also account for electronic noise and variations in analog parameters across channels.
[1] S. S. Hsieh and K. Iniewski, “Improving Paralysis Compensation in Photon Counting Detectors,” IEEE Trans Med Imaging, vol. 40, no. 1, pp. 3–11, Jan. 2021, doi: 10.1109/TMI.2020.3019461.
[2] R. Ballabriga et al., “Photon Counting Detectors for X-Ray Imaging with Emphasis on CT,” IEEE Trans Radiat Plasma Med Sci, vol. 5, no. 4, pp. 422–440, Jul. 2021, doi: 10.1109/TRPMS.2020.3002949.
[3] P. Grybos, R. Kleczek, P. Kmon, P. Otfinowski, and P. Fajardo, “Small pixel high-spatial resolution photon-counting prototype IC for synchrotron applications,” Journal of Instrumentation, vol. 18, no. 1, Jan. 2023, doi: 10.1088/1748-0221/18/01/C01052.
[4] A. Krzyzanowska and P. Otfinowski, “Digital subpixel algorithm for small pixel photon counting devices,” Opto-Electronics Review, vol. During revision, 2024.