Clinical Use of a J-PET Scanner Prototype Made of Plastic Scintilators

Positron emission tomography (PET) is currently one of the basic techniques enabling molecular imaging. This concept means imaging at the level of biochemical processes. 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.

Current PET cameras possess remarkable sensitivity, enabling the detection of changes in chemical concentration as subtle as 1E-11 moles. This unprecedented sensitivity allows for the visualization of metabolic alterations, neurotransmitter imbalances, or receptor system dysfunctions at an early stage, often before the onset of clinical symptoms in various diseases. The PET technique relies on radioisotopes that emit positrons, which are the antimatter counterparts of electrons. PET cameras, tasked with monitoring positron distribution, employ detector systems that capture the radiation generated during positron-electron annihilation. This annihilation process occurs in the emission of gamma ray photons, which are detected by the appropriate detector arrays. The computer system particularly records only those events that simultaneously trigger two detectors, ensuring high spatial resolution and precise anatomical localization of the annihilation events. Notably, positron annihilation may be preceded by the formation of positronium, a transient, quasi-stable bound state comprising an electron and its antiparticle, the positron. Due to the mutual arrangement of spins, two states of the positron are distinguished.

• When the electron and positron spins are parallel (triplet state ↑↑); this arrangement is called ortho-positronium (o-Ps). o-Ps decays (annihilation occurs) after an average vacuum lifetime of 142 nanoseconds [ns]. Annihilation produces three gamma ray photons.
• When the spins of the electron and positron are antiparallel (singlet state ↑↓) - the system is called para-positronium (p-Ps). Annihilation produces two gamma-ray photons with an average vacuum lifetime of 125 picoseconds [ps], or 1,136 times shorter.

Distinct from conventional PET scanners employed in diagnostic imaging, the J-PET scanner boasts three remarkable features:

1. Plastic Scintillation: unlike standard PET scanners that use expensive scintillation crystals, the J-PET scanner utilizes plastic scintillators, significantly lowering its cost and making it more affordable.
2. Modular Design: J-PET's modular design allows for easy customization to fit different patient sizes and can be expanded to a whole-body PET scanner. This flexibility caters to a wide range of patient populations and diagnostic needs.
3. Positronium Biomarker: J-PET expands the scope of PET imaging by introducing the detection and analysis of o-Ps.