Fig. 5. Modular J-PET tomograph.

(A) Photograph of the modular J-PET system with a human placed inside the scanner. The superimposed blue dashed arrows indicate photons from the electron-positron annihilation (e⁺e⁻ →γγ), while the red solid arrow indicates prompt gamma (γ_p) from the decay of the ⁶⁸Ga radionuclide. The modular J-PET scanner enables registration and identification of both γγ and γγ+γ_p events, which are used in this study for the standard PET imaging (γγ) and positronium imaging (γγ+γ_p). (B) Cross section of the modular J-PET showing the 24-module structure of the scanner, where each module is composed of 13 scintillator strips. Scintillators that register the photons are marked in yellow in (A) and (B). (C) Block diagram of the data processing (43). Light signals generated by gamma photons in the tomograph are collected by a triggerless DAQ system (20) and stored on discs in the form of the continuous sequence of timestamps. Timestamps are used for signal reconstruction including the place and time of gamma photon interaction. Signals are then used for event reconstruction. Next, the true γγ and γγ+γ_p events are selected by event selection algorithms. Last, the selected events, in the list mode format, are used for the standard 2γ PET image reconstruction and positronium image reconstruction.