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Positronium imaging in J-PET with an iterative activity reconstruction and a multistage fitting algorithm

Shopa Roman Y., Dulski Kamil

Bio-Algorithms and Med-Systems

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2023

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Vol. 19, no. 1

54--63

EN

Positronium imaging is a new technique complementary to positron emission tomography (PET) based on the histogramming of time delay between the emission of a de-excitation photon, and a consequent electron-positron annihilation, to estimate the mean lifetime of orthopositronium (o-Ps), which depends on the local size of the voids, concentration of oxygen and bioactive molecules. We improve the resolution and reduce noise in positronium imaging by building time-delay spectra from the PET activity reconstructed by a 3-photon time-of-flight maximum likelihood expectation maximisation. The method was tested on the data measured for four human-tissue samples injected by 22Na and put in the Jagiellonian PET “Big barrel” scanner. Due to an ill-posed problem of fitting time-delay histograms, a multistage optimisation procedure was explored along with inferential analysis of the solution space. Run in parallel for multiple sets of initial guesses, we compared the second-order LevenbergMarquardt algorithm (LMA) and the direct search Nelder-Mead simplex (NMS) method. The LMA proved to be faster and more precise, but the NMS was more stable with a higher convergence rate. The estimated mean o-Ps lifetimes in the 1.9 ns - 2.6 ns range were consistent with the reference results, while other fitting parameters allowed differentiation between the two patients who provided the tissue samples.

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Optimization of positronium imaging performance of a simulated modular J-PET scanner using GATE software

Parzych Szymon

Bio-Algorithms and Med-Systems

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2023

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Vol. 19, no. 1

80--86

EN

Recently, a novel PET imaging method - positronium imaging - has been proposed to take advantage of previously unused information about the positronium states. The first ex-vivo and in-vivo images of positronium characteristics were acquired with the J-PET tomograph. Complementary to the standard annihilation photon’s detection, positronium imaging also requires the registration of the prompt photon, which follows β+ decay. To that end, the introduction of an additional energy threshold for prompt γ registration and optimization of the energy window for annihilation γ are required. This simulation-based work undertook the mentioned task in the case of the modular J-PET scanner. Based on the 44Sc radioisotope, the energy window for annihilation photons was established to 0.2 MeV - 0.37 MeV, while the threshold for prompt gamma was fixed at 0.37 MeV, closely following the end of the energy window for annihilation photons.

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Estimating the efficiency and purity for detecting annihilation and prompt photons for positronium imaging with J-PET using toy Monte Carlo simulation

Das Manish, Mryka Wiktor, Beyene Ermias Y., Parzych Szymon, Sharma Sushil, Stępień Ewa, Moskal Paweł

Bio-Algorithms and Med-Systems

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2023

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Vol. 19, no. 1

87--95

EN

The positronium imaging technique represents a potential enhancement of the PET imaging method. Its core principle involves employing a β+ radiation source that emits additional gamma (γ) quanta referred to as prompt gamma. Our aim is to evaluate the capability to differentiate between annihilation and prompt gamma emissions, a vital aspect of positronium imaging. For this purpose, the selected isotopes should enable high efficiency and purity in detecting both prompt gamma and annihilation gamma. The assessment of the efficiency in identifying prompt and annihilation photons for various isotopes, which are potentially superior candidates for β++ γ emitters, is conducted through toy Monte-Carlo simulation utilizing the cross-section formula for photon-electron scattering. In this article, we have performed calculations for efficiency and purity values across different isotopes under ideal conditions and examined how these values evolve as we incorporate the fractional energy resolution into the analysis. Ultimately, the primary goal is to determine the energy threshold that optimizes both efficiency and purity, striking a balance between accurately identifying and recording events of interest while minimizing contamination from undesired events.

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Unparalleled and revolutionary impact of PET imaging on research and day to day practice of medicine

Alavi Abass, Werner Thomas J., Stępień Ewa Ł., Moskal Paweł

Bio-Algorithms and Med-Systems

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2021

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Vol. 17, no. 4

203--212

EN

Positron emission tomography (PET) imaging is the most quantitative modality for assessing disease activity at the molecular and cellular levels, and therefore, it allows monitoring its course and determining the efficacy of various therapeutic interventions. In this scientific communication, we describe the unparalleled and revolutionary impact of PET imaging on research and day to day practice of medicine. We emphasize the critical importance of the development and synthesis of novel radiotracers (starting from the enormous impact of F-Fluorodeouxyglucose (FDG) introduced by investigators at the University of Pennsylvania (PENN)) and PET instrumentation. These innovations have led to the total-body PET systems enabling dynamic and parametric molecular imaging of all organs in the body simultaneously. We also present our perspectives for future development of molecular imaging by multiphoton PET systems that will enable users to extract substantial information (owing to the evolving role of positronium imaging) about the related molecular and biological bases of various disorders, which are unachievable by the current PET imaging techniques.