Self-thresholding, 48:2 multiplexed readout circuit for a 3D position sensitive, 100 ps CTR TOF-PET detector

Abstract

To achieve precise three-dimensional (3D) position resolution for one or more annihilation photon interactions in a 100 ps coincidence time resolution (CTR) time-of-flight positron emission tomography (TOF-PET) detector design, we have developed a 3D position-sensitive scintillator readout circuit using a low power charge-division (anger-based) scheme. This compact charge-division block, implemented with on-board real-timeX/Yprocessing, reduces system complexity, area, and power while enabling continuous resolution of <2 mm full width at half maximum along the radial [depth of interaction (DOI)] direction in 3 × 3 × 10 mm³LGSO crystal elements. The mixed-signal TOF-PET system integrates custom low-noise, low-power front-end electronics including independently self-thresholding 48:2 multiplexed timing and 48:2 multiplexed energy/3D positioning plus biasing circuits and flex-cable interconnects. Our auto-thresholding architecture effectively mitigates signal amplitude and baseline variations, ensuring stable CTR performance and removing the need for complex external threshold tuning common in conventional systems. For experimental validation, we used 2 × 4 arrays of 3 × 3 × 10 mm³LGSO crystals side-coupled to 4 × 6 arrays of 3 × 3 mm²silicon photomultipliers (SiPMs) (20 mm effective fast LGSO radial dimensions). Using our 48:2 multiplexed timing readout, we achieved an average CTR of 102.5 ± 2.7 ps full width at half maximum (FWHM) across a 30-31.5 V SiPM bias range (<5 ps FWHM overall variation), demonstrating strong robustness of our TOF-PET detector readouts. Independently, through the formulated charge-division networks, we achieved energy resolutions of 18% FWHM using time-over-threshold (TOT) and 13% FWHM using dynamic TOT at 511 keV, with the latter resolving events down to 31 keV energy, while achieving average ∼1.6 ± 0.3 mm FWHM continuous DOI resolution. Overall, the system maintains ∼100 ps FWHM CTR performance while reducing component count, footprint, power consumption, and cost by at least 40% compared to both our previous complex programmable logic device-based and other 3D discretized positioning circuit-based readouts. Each 48:2 multiplexed detector unit provides timing and positioning outputs through minimal I/Os with only 1.7 W power dissipation.

Keywords: 100 ps coincidence time resolution; 3D position sensitive; DOI; multiplexed front-end electronics; positron emission tomography; self-thresholding; time-of-flight.