Clinical Application of the Prototype J-PET Device

Overview

Positron emission tomography (PET) is a diagnostic imaging technique that uses positron emission (e-) to image changes in diagnosed tissues. Detector systems are an important part of PET scanners. They can convert gamma photons into fluorescent photons to obtain information about energy, time and position, of the gamma photons obtained through the use of an appropriate positron-emitting radiopharmaceutical. Conventional PET scanners are expensive mostly because they require the use of LSO (lutetium oxyorthosilicate) or LYSO (lutetium yttrium oxyorthosilicate) scintillation crystals. Such crystal scintillators are very costly and difficult to obtain, which limits accessibility of the PET- scanners. The prototype J-PET scanner tested in this trial uses plastic scintillators in which different physical phenomena occur compared to crystal scintillators. In addition, the J-PET scanner prototype is equipped with unique software enabling three-photon imaging, based on the annihilation resulting from the formation of the orto-positronium (o-Ps) in diagnosed tissue. The aim of this study is to demonstrate the clinical acceptability of such scanners based on plastic scintillators, which can additionally collect and process information on the lifetime of o-Ps derived from routinely used radiopharmaceuticals. Additionally, the aim of this study is to demonstrate the use of the new diagnostic indicator "positronium biomarker" in a prospective study, compared to routine diagnostic scanning.

The J-PET scanner is the world's first positron tomograph based on plastic strip scintillators to measure the lifetime of the ortho-positronium (o-Ps) atom. This is a modular scanner, designed and installed at the Department of Experimental Particle Physics and Applications of the Jagiellonian University in Krakow. The J-PET scanner is based on technology patented in 2014 and 2016. The J-PET scanner, unlike PET scanners commonly used in diagnostics, has three important features: 1. J-PET scintillators are made of plastic instead of expensive-to-produce LSO (lutetium oxyorthosilicate) or LYSO (lutetium yttrium oxyorthosilicate) scintillation crystals use in regular PET scanners; 2. J-PET is modular and can be adapted to the patient's size and expanded to a total-body PET scanner because; 3. J-PET can be used to test an additional parameter called the "positronium biomarker" which has not been used so far. Ad. 1. Conventional PET scanners use LSO or LYSO scintillation crystals, which exploit the photoelectric effect and convert gamma photons into fluorescent photons to obtain information on the energy, time and position of gamma photons emitted by the positron annihilation (e+) process obtained by using an appropriate e+ emitting radiopharmaceutical. In plastic scintillators used in J-PET, the Compton effect is used, i.e. the phenomenon of scattering of high-energy photons on free or weakly bound electrons of the scintillator. Ad. 2. The modular J-PET scanner can also be easily integrated with existing computed tomography (CT) systems, allowing for simultaneous conduction of both types of examinations. Ad. 3. Positronium imaging is applied in the J-PET scanner. The PET technique uses radioisotopes that emit positron radiation (beta+). Traditional PET scanners image the distribution of gamma ray photons produced by the annihilation of an electron (e-) and a positron (e+). Annihilation may be preceded by the appearance of a positron atom - a quasi-stable system composed of an electron (e-) and its antiparticle - positron (e+), which occurs in approximately 30-40% of all annihilations occurring in the patient's body. The time of such annihilation taking place through the state of the positronium atom depends on whether a positronium will be created in which e- and e+ will have parallel spins (triplet state ↑↑, this system is called ortho-positronium - o-Ps) or antiparallel spins (state singlet ↑ ↓, this system is called para-positronium - p-Ps). The average life time of o-Ps in vacuum is more then 1000 times longer (142 nano-seconds \[ns\]), then the average life time of p-Ps (125 pico-seconds \[ps\]). The average lifetime of o-Ps in a vacuum is over 1000 times longer (142 nanoseconds \[ns\]) than the average lifetime of p-Ps (125 picoseconds \[ps\]). The second difference is that o-Ps annihilation takes place over 3 photons, which has not been detected so far and which traditional PET. the annihilation time of the o-Ps atom can be an additional diagnostic parameter ("positronium biomarker") to be measured and analyzed in the J-PET scanner. The clinical application of such "positronium biomarker" in terms of lesion detection, image quality and quantification is yet to be determined, which this study aims to address.