Multi-photon time-of-flight MLEM application for the positronium imaging in J-PET

Abstract We develop a positronium imaging method for the Jagiellonian PET (J-PET) scanners based on time-of-flight maximum likelihood expectation maximisation (TOF MLEM). The system matrix elements are calculated on-the-fly coincidences comprising two annihilation and one de-excitation photons that originate from ortho-positronium (o-Ps) decay. Using Geant4 library, Monte Carlo simulation was conducted four cylindrical 22 Na sources of β + decay with diverse o-Ps mean lifetimes, placed symmetrically inside JPET prototypes. estimated time differences between positron emission were aggregated into histograms (one per voxel), updated by weights activities reconstructed TOF MLEM. simulations restricted to include only decays back-to-back photons, allowing linear fitting model be employed estimation lifetime each histogram built in log scale. To suppress noise, exclusion voxels activity below 2% – 10% peak studied. lifetimes consistent distributed quasi -uniformly at high MLEM iterations. proposed technique can further upgraded various correction factors, as well modified according realistic models.