Faculty of Physics, Astronomy
and Applied Computer Science

This manuscript introduces a novel method to assess tissue oxygen concentration via the quantum entanglement (QE) of photons originating from positronium which is produced within the patient's body during positron emission tomography. We also investigate the possibility of assessing hypoxia by simultaneously detecting positronium lifetime and the positronium decay rate ratio. We introduce two distinct quantum sensing approaches. Method 1 utilizes the correlation between oxygen concentration and ortho-positronium (o-Ps) decay rates, relying on the simultaneous measurement of the mean o-Ps lifetime ( ) and the -to- annihilation rate ratio of o-Ps ( ). Method 2 introduces a novel hypothesis: that the degree of QE is sensitive to the relative contribution of annihilation mechanisms (pick-off vs. conversion), which in turn depends on oxygen concentration. We derive a formula for partial pressure of oxygen ( ) as a function of and and estimate the measurement accuracy required for these parameters - and for the degree of QE - to sense in-vivo oxygen pressure in the range between hypoxic and physoxic conditions. Theoretical models and quantitative estimates for , and for the degree of QE ( ) as a function of are provided for water, isopropanol, cyclohexane, isooctane, and adipose tissue. In particular, applying the formulas derived under the working hypothesis that in pick-off process the photons are not entangled, we estimated that for , the degree of quantum entanglement is equal to 0.890 for adipose, 0.886 for isopropanol, 0.867 for water, 0.818 for cyclohexane, and 0.784 for isooctane.

This study demonstrates applicability of 52Mn and 55Co radionuclides for positronium imaging. Positronium Lifetime Imaging (PLI) extends positron emission tomography by using the lifetime of positronium atoms as a probe of tissue molecular architecture. However, its practical use requires ?+ emitters that also provide an additional prompt ? ray to mark the positron creation time. In this work, we report the first PLI measurements performed with 52Mn and 55Co using the modular J-PET. Four samples were studied in each experiment: two Certified Reference Materials (polycarbonate and fused silica) and two human tissues (cardiac myxoma and adipose). The selection of PLI events was based on the registration of two 511 keV annihilation photons and one prompt gamma in triple coincidence. From the resulting lifetime spectra we extracted the mean ortho-positronium lifetime ?oPs and the mean positron lifetime ?Tmean for each sample. The measured values of ?oPs in polycarbonate using both isotopes matches well with the certified reference values. Furthermore, 55Co reproduced identical results for fused-silica measurements at their respective uncertainty levels. In contrast, measurements with 52Mn in fused silica show a minor deviation, which could be caused by the Parafilm spacer. In myxoma and adipose tissue, the reduced ?oPs values are mainly linked to the long storage history of the samples rather than to the choice of isotope. Comparing peak-to-background ratios and spectral purity, 55Co provides cleaner PLI data under the same experimental conditions. Although 52Mn offers a longer half-life and a multi gamma cascade enhancing ?+ + ? coincidences, but at the expense of higher background. In this study, we demonstrate that the applied selection criteria on the data measured with the modular J-PET can be used for PLI studies even with radionuclides with complex decay patterns.

This study presents the first ex-vivo positronium imaging of human tissues using the modular J-PET scanner with the 44Sc radionuclide. The 44Sc isotope was produced via the 44Ca(p, n)44Sc nuclear reaction and used to perform positronium imaging of phantom composed of human adipose tissue, cardiac myxoma tissue, thrombi blood clot, and also porous polymer XAD4, and a certified reference material (CRM) made from fused silica. The experiment demonstrates the suitability of 44Sc as a positron source for positronium imaging. The performance of J-PET for positronium imaging with 44Sc was validated by proper reconstruction of the mean orthopositronium lifetime for CRM material and XAD-4 polymer. The mean ortho-positronium (oPs) lifetimes determined for adipose tissue, cardiac myxoma tissues and thrombi were consistent with results of previous experiments. The study highlights the potential Sc radionuclide for positronium lifetime imaging (PLI).

The development of PET and positronium imaging techniques is strictly related to the availability of suitable radionuclides and robust radiochemistry platforms. Among the emerging candidates, 44Sc has attracted significant interest due to its favourable physical properties, including a half-life of 4 hours, a pure emission profile, and the additional prompt -emission that enables advanced triple-photon detection schemes. These characteristics make 44Sc particularly promising for highresolution imaging and novel quantitative methodologies. However, routine clinical and preclinical implementation requires a practical, sustainable, and cost-efficient production route. In this context, we propose a titanium-scandium radionuclide generator as an optimal solution. This study focuses on optimising the synthesis of the long-lived parent isotope, 44Ti (T1/2 = 59.1 years), from which 44Sc can be selectively eluted in a chemically pure form when needed. An analysis of various production pathways was conducted, including proton and deuteron reactions on scandium, as well as alpha-particle and lithium-induced reactions on calcium, to determine the most efficient reaction parameters, target design, and expected yield. Furthermore, we identify some existing cyclotron facilities suitable for implementing this technology. Results indicate that efficient Ti production is achievable using proton beams in the 20-30 MeV range under extended irradiation conditions. The proposed generator system would enable routine and decentralised 44Sc supply. Its integration with the novel J-PET scanner may significantly reduce diagnostic costs and improve access to advanced PET imaging in regions with limited medical imaging infrastructure.

Understanding the entangled polarization of photons produced in positron?electron annihilation remains experimentally challenging. Recently, it has been proposed to utilize this correlation in positron emission tomography imaging to suppress the random background and as a diagnostic parameter. Conventional positron emission tomographs rely on the registration of the two annihilation photons from positron annihilation. However, measuring polarization correlations requires scattering of annihilation photons in the detector volume and the registration of their corresponding scatters. Such a 4-hit event topology inherently suffers from low efficiency and high background. Therefore, translating this quantum information into medical imaging requires a method to overcome the inherent limitations of conventional geometric cuts. We present a machine learning classification framework trained on simulated detector events. This approach enables a high-purity separation of polarization-correlated signal from background and simultaneously achieves a significant improvement in computational efficiency.

Objective: Positron Emission Tomography enables non-invasive imaging of metabolic processes. Standard PET reconstructs radiotracer distribution using two back-to-back photons from electron-positron annihilation. However, about 1% of annihilations results in creation of three photons. Three photons may be created in direct annihilation and in annihilation via formation of metastable ortho-positronium carrying additional information not used by conventional PET. The Jagiellonian-PET detector allows us to use this information by applying positronium imaging based on ortho-positronium lifetime or the 3gamma/2gamma decay ratio. Accurate tomographic images require attenuation correction. This study investigates photon absorption in phantom models to form a basis for future attenuation maps for three-gamma decays. Methods: Monte Carlo simulations in ROOT and GATE were performed for water sphere, cylinder, a simplified head model, and the mesh50_XCAT phantom. Both p-Ps and o-Ps decays were simulated as uniformly distributed sources. Absorption probabilities were calculated by checking whether any photon in a multiplet interacted within the phantom. Emission-point-specific absorption maps were generated for all models. Toy Monte Carlo and GATE simulations showed good overall agreement. Results: Photon triplets from o-Ps decays experienced higher absorption than photon pairs from p-Ps due to lower individual energies and higher attenuation. Absorption maps showed dependence of photon survival probability on the decay location. In the mesh50_XCAT phantom, 24.9% of p-Ps pairs and 10.3% of o-Ps triplets escaped without interaction. Conclusions: Gamma absorption depends strongly on positronium decay mode and location, with o-Ps events experiencing higher attenuation. The generated absorption maps provide the first step toward dedicated attenuation correction for three-gamma positronium imaging, enabling accurate reconstruction in novel 3?/2? positronium imaging technique. A Study presented indicates that the absorption of 3gamma in the head is only about 2.5 times higher than for the 2gamma, which is encouraging for further development of the 3gamma/2gamma rate ratio imaging.

Objective: Quantitative PET requires accurate attenuation correction (AC), which is conventionally achieved using CT-derived maps, incurring extra dose and complexity. This study explores a CT-less AC approach for the plastic scintillator-based J-PET scanner by investigating whether detector-scattered photons (DS-LORs) can serve as an intrinsic transmission source. Methods: Simulation Setup: The study utilized GATE v9.1 software to simulate the modular J-PET scanner, which consists of plastic scintillator strips where 511 keV photons predominantly undergo Compton scattering. Two configurations were evaluated: a uniform water cylinder and a NEMA IQlike phantom containing a cold lung insert and six hot spheres to simulate heterogeneous activity. Analysis & reconstruction: The study isolated triple-hit coincidences to analyze angular deviations. DS-LORs were identified using a specific scatter test metric based on interaction positions and detection times. Attenuation maps were reconstructed using Filtered Back Projection (FBP) applied to the ratio of water-to-air sinograms. Results: Due to the properties of plastic scintillators, DS-LORs constituted approximately 50% of all detected prompts, providing a substantial dataset for analysis. In a simulated 10-minute acquisition, the noise propagation analysis yielded a Signal-to-Noise Ratio (SNR) of ? 33.9 for water. This is significantly higher than conventional crystal-based PET, which yields only ? 5% DS-LORs and a lower SNR. Reconstructions successfully resolved the NEMA phantom features, including the cold lung insert and hot spheres, particularly when phantom-scattered events were rejected. Conclusions and future directions: This study confirms that DS-LORs retain sufficient attenuation information to estimate ?-maps, demonstrating the potential for fully CT-less PET imaging. While the current implementation faces limitations like reliance on blank scans and activity-attenuation crosstalk, the high statistics of DS-LORs are a foundation for developing joint reconstruction algorithms aiming towards clinical application.