Digital asynchronous event-based circuits for photon detection in modern CT scans

Abstract

This study explores the integration of asynchronous event-driven circuitry with photon-counting technology to enhance detection performance in modern computed tomography (CT) systems. Asynchronous circuits are wellsuited for event-driven applications, including photon-counting imaging. However, conventional architectures such as the threshold subtraction (TS) and direct binning (DB) schemes have not been implemented at the circuit level, and their performance is limited by challenges such as pulse pile-up and charge crosstalk.

To address these limitations, we propose a novel pileup-specific (PS) system that mitigates pile-up effects by extracting both the onset and peak information of pulse events. Furthermore, the multi-energy inter-pixel coincidence counters (MEICC) system, a state-of-the-art solution for charge crosstalk, is shown to be highly compatible with our PS design. Using the open-source asynchronous circuit toolkit (ACT), we successfully implemented the TS, PS, and MEICC systems as asynchronous digital circuits. Transistor-level simulations demonstrate that the proposed PS system significantly improves counting accuracy under pile-up conditions compared to the conventional TS approach, with only minor trade-offs in speed and area. Additionally, benchmark comparisons with synchronous designs indicate that the asynchronous implementations offer superior power efficiency and operational robustness in photon-counting applications. These results highlight the potential of asynchronous event-driven circuits to enable the next generation of CT imaging systems with improved accuracy, energy efficiency, and reliability.