Development of Real-Time Imaging Technology Using an Omnidirectional Detector

We developed and evaluated a real-time gamma-ray directional imaging framework using the Fractal Radiation Imaging Element (FRIE), an omnidirectional detector based on a Sierpinski tetrahedral structure. The system consists of sixteen scintillator crystals, each acquiring spectral data every second, and estimates the incident gamma-ray directions at 1-s intervals by analyzing variations in detector response. The estimated directional distributions are superimposed on images captured by a 360-degree camera, enabling intuitive visual confirmation. In this study, real-time imaging performance was comparatively evaluated using multiple analysis algorithms, including the conventional Maximum Likelihood Expectation Maximization (MLEM) method and similarity-based analyses employing pre-acquired reference response patterns with correlation coefficients, Euclidean distance, and Wasserstein distance. Although all methods were able to estimate the incident directions in real time, the similarity-based analyses-particularly the approach combining Euclidean and Wasserstein distances-demonstrated higher stability and reproducibility, with angular errors constrained within approximately 20 degrees. These results indicate that similarity-based analysis is effective for robust and real-time localization of radiation sources using the FRIE detector.