Feasibility simulation study of positronium lifetime imaging with the Biograph Vision Quadra and J-PET tomographs

Background After its first ex-vivo and in-vivo demonstration, Positronium Lifetime Imaging (PLI) has received considerable interest as a potential new diagnostic biomarker. High sensitivity Positron Emission Tomography (PET) systems are needed for PLI since it requires simultaneous registration of annihilation photons and prompt gamma. In this simulation-based study, a feasibility of PLI with the long axial field-of-view Biograph Vision Quadra (Quadra) and the Total Body J-PET scanner was investigated. Methods The study was performed using the GATE software. Background radiation, present within the Quadra tomograph, was added to the simulation. First, the optimal placement of the energy window for the registration of the prompt gamma was investigated. Next, the organ-wise sensitivity of Quadra was calculated for the ⁶⁸ Ga, ⁴⁴ Sc, ²² Na and ¹²⁴ I radioisotopes. Finally, the sensitivity for the scandium isotope was compared to the sensitivities obtainable with the Total Body J-PET scanner, as well as with the modular J-PET prototype. Results The PLI sensitivities for the Quadra with the background radiation are estimated to 9.22(3), 10.46(4), 5.91(3), and 15.39(4) cps/kBq for the ⁴⁴ Sc, ⁶⁸ Ga, ²² Na and ¹²⁴ I radioisotopes, respectively. The highest sensitivity was obtained when the energy window for the deexcitation photon is adjacent to the energy window for the annihilation photons. In case of J-PET, the sensitivities for the ⁴⁴ Sc were estimated to 0.062(08) and 1.714(40) cps/kBq for the modular and Total Body J-PET scanners, respectively. The determined PLI sensitivities with Quadra and the Total Body J-PET are in the order of sensitivities of metabolic PET imaging with the short axial field-of-view ( ~ 20 cm) PET scanners based on pure positron emitter isotopes. Conclusions The PLI sensitivity of Quadra has been computed for the ⁶⁸ Ga, ⁴⁴ Sc, ²² Na and ¹²⁴ I radioisotopes. A sensitivity gain by a factor of 150 was estimated relative to the modular J-PET system previously used for the first in-vivo PLI. Additionally, the sensitivity for Total Body J-PET is expected to be about 30 times higher than for modular J-PET.