Beyond NEMA: robustness, DOI encoding, and multi-mouse imaging performance of the Bruker PET/CT Si78.

OBJECTIVE: This work presents a comprehensive evaluation of the Bruker PET/CT Si78 preclinical imaging system, combining standardized performance assessment, inter-system reproducibility analysis, and investigation of depth-of-interaction (DOI) encoding effects on image quality. APPROACH: Ten independently assembled systems were characterized following the National Electrical Manufacturers Association NU 4-2008 protocol to assess spatial resolution, sensitivity, count rate performance, and image quality. Beyond standard evaluation, this study investigates the impact of DOI estimation using simulations, controlled experiments, and in vivo multi-mouse imaging. MAIN RESULTS: The results demonstrate consistent performance across the evaluated systems, with nearly uniform spatial resolution across the field of view, peak sensitivity around 10.5%, and low variability among systems, typically below 5%, indicating low inter-system variability across most evaluated metrics. Continuous DOI estimation, enabled by monolithic detector technology, improves spatial resolution and its uniformity compared with dual-layer and non-DOI approaches, particularly at the periphery of the imaging volume where parallax effects are most pronounced. These improvements were consistently observed in both simulated and experimental datasets. The practical implications of DOI encoding were demonstrated in multi-animal imaging studies, where enhanced visualization of fine anatomical structures and improved quantitative accuracy were achieved. In particular, the absence of DOI information led to substantial spatially dependent quantification errors, while dual-layer DOI partially mitigated these effects. Continuous DOI estimation provided the smallest deviations and most spatially uniform results among the evaluated configurations, supporting reliable quantification in demanding applications such as brain imaging. SIGNIFICANCE: Overall, the PET/CT Si78 system combines competitive performance with high reproducibility and advanced DOI capabilities, enabling uniform image quality across the field of view and supporting efficient multi-animal studies. These characteristics supports its use for reproducible and ethically optimized preclinical imaging aligned with the principles of reduction and refinement in animal research.