Instrumentation Digital Twins in PET and SPECT Imaging: Current Status, Challenges, and Future Directions

Introduction: Digital twins (DTs) in nuclear medicine are data-synchronized, physics-based models that replicate positron emission tomography (PET) and single-photon emission computed tomography (SPECT) systems by linking validated simulations with scanner configuration and calibration inputs. Instrumentation DTs (iDTs) extend system modeling by enabling feedback-driven assessment of detector performance, collimation, electronics behavior, and acquisition conditions. This review summarizes recent developments in PET and SPECT iDTs and evaluates their roles in system optimization. Materials and Methods: A structured literature review was conducted, and applications were grouped into 6 domains: (a) calibration and performance optimization, (b) predictive maintenance and fault detection, (c) quantitative correction and protocol optimization, (d) dosimetry and reconstruction benchmarking, (e) synthetic data generation and artificial intelligence (AI) training, and (f) scanner design and geometry evaluation. Attention was given to implementations integrating established detector and system models into unified, data-linked workflows. Results: Evidence shows that iDTs support virtual calibration, protocol assessment, and algorithm benchmarking. They can simulate detector misalignment and probabilistic hardware failures, factors relevant for high-resolution and small-animal imaging. iDTs also enable exploration of geometry changes, dose-sensitivity trade-offs, and long axial field-of-view configurations. However, current approaches remain fragmented, depend on vendor-specific components, and provide limited telemetry integration. Validation still relies mainly on standard National Electrical Manufacturers Association and quality control procedures. Conclusion: Future progress will benefit from modular and standardized iDT frameworks incorporating hardware realism, reliability modeling, and hybrid AI-physics strategies. Fully developed iDTs can improve calibration stability, support adaptive protocol design, enable early detection of component degradation, guide dose optimization, and accelerate virtual prototyping of next-generation PET and SPECT systems.