Radioactive source estimation using a system of directional and non-directional detectors

We derive Maximum Likelihood based source estimation algorithms for a system of Non-Directional (CsI based scintillation detectors) and Directional (CZT based Compton detectors) radiation detectors. For multiple non-directional detectors, source is estimated by grid search on the joint log-likelihood of registered counts to find the MLE. For directional detectors, the well-known List Mode Maximum Likelihood Expectation Maximization Algorithm (MLEM) is extended to fuse information from multiple detectors and estimate the source in cartesian coordinates. Here, the angular event likelihoods from Compton scattering are projected into a common Cartesian grid followed by List Mode MLEM computations. We also derive multi-sensor fusion algorithms for a mix of both non-directional and directional detectors using combinations of MLE and MLEM methods. Results are presented which illustrate the behavior and performance of our proposed approaches.