Optimising the event selectionof the total-body J-PET scannerwith a brain PET insert:A simulation study

<ns3:p> Objective: Positron emission tomography (PET) scanners with plastic scintillators offermore cost-effective instrumentation to image the distribution of radiopharmaceuticals.However, inter-detector scatters among plastic scintillators can lead to more falsecoincidences than in conventional PET scanners, since annihilation photons in plasticscintillators dominantly interact via Compton scattering, which deposits only a portionof the photon energy. A scatter test (ST), combined with a lower energy depositionthreshold of 200 keV, has been used to preselect the coincidence events. Methods: In this work, we investigate the impact of temporal and spatial resolutionlimitations as well as a variation of the energy threshold on the preselection anddifferent subsequent coincidence event selection policies via Monte Carlo simulations.We simulate the total-body Jagiellonian-PET (TB-J-PET), combined with a brain PETinsert imaging a human-sized water phantom. Results: We find that coincidence time resolution (CTR) worse than 200 ps poseslimitations on the ST for scanners close to the patient, such as the brain PET. Also,coincidence event selection requiring energy loss higher than 200 keV performs suboptimally,whereas a lower energy threshold (50 keV), combined with a time-basedselection policy, can capture a higher percentage of true events, even under realistictime resolution. Conclusions: We recommend the adaptation of a time-based event selection policytogether with a lowered energy threshold, which can also significantly increasesensitivity, as the latter rises faster than the fraction of true and non-phantom--scattered events decreases. Dedicated analyses in the scatter-corrected imagedomain are necessary to further investigate this potential. </ns3:p>