Abstract
A detection system of the conventional PET tomograph is set-up to record data from annihilation into two photons with energy of 511 keV, and it gives information on the density distribution of a radiopharmaceutical in the body of the object. In this paper we explore the possibility of performing the three gamma photons imaging based on ortho-positronium annihilation, as well as the possibility of positronium mean lifetime imaging with the J-PET tomograph constructed from plastic scintillators. For this purposes simulations of the ortho-positronium formation and its annihilation into three photons were performed taking into account distributions of photons’ momenta as predicted by the theory of quantum electrodynamics and the response of the J-PET tomograph. In order to test the proposed ortho-positronium lifetime image reconstruction method, we concentrate on the decay of the ortho-positronium into three photons and applications of radiopharmaceuticals labeled with isotopes emitting a prompt gamma. The proposed method of imaging is based on the determination of hit-times and hit-positions of registered photons which enables the reconstruction of the time and position of the annihilation point as well as the lifetime of the ortho-positronium on an event-by-event basis. We have simulated the production of the positronium in point-like sources and in a cylindrical phantom composed of a set of different materials in which the ortho-positronium lifetime varied from 2.0 ns to 3.0 ns, as expected for ortho-positronium created in the human body. The presented reconstruction method for total-body J-PET like detector allows to achieve a mean lifetime resolution of ∼40 ps. Recent positron annihilation lifetime spectroscopy measurements of cancerous and healthy uterine tissues show that this sensitivity may allow to study the morphological changes in cell structures.
Highlights
Positron emitted inside the human body can either annihilate directly with one of the electrons of the examined organism or it creates the metastable state of electron and positron called positronium (Ps)
In this article we explore a possibility of positronium average lifetime imaging with the J-PET tomograph constructed from plastic scintillators (Moskal et al 2016, Niedźwiecki et al 2017)
In this article we presented a cost-effective method enabling reconstruction of the density distribution of the e+e− → 3γ annihilation points, as well as reconstruction of the image of ortho-positronium average lifetime
Summary
Positron emitted inside the human body can either annihilate directly with one of the electrons of the examined organism or it creates the metastable state of electron and positron called positronium (Ps). The average lifetime of positronium depends on the size of the free volumes between atoms (Tao 1972, Eldrup et al 1981, Schrader and Jean 1988, Coleman 2000) and there are indications (Liu et al 2007, Pietrzak et al 2013, Jasińska et al2017a, 2017b) that it is correlated with the stage of the development of metabolic disorders of the human tissues. An image of the average lifetime and production probability of the positronium formed inside the human body during the routine PET imaging (Moskal et al 2013), as well as the fraction of its annihilations into three-photons (Kacperski and Spyrou 2005, Jasińska and Moskal 2017) may deliver information complementary to the standardized uptake value (SUV) and useful for the diagnosis. We concentrate on the decay of the ortho-positronium (o-Ps) into three photons and applications of radiopharmaceuticals emitting prompt gamma
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