A Conjugate Bayesian Framework for Fast 3D Positronium Lifetime Estimation with a Partial System Matrix
Berkin Uluutku, Giulianno Gasparato, Manish Das, Jarosław Choiński, Anand Pandey, Sushil Sharma, Paweł Moskal, Ewa Stępień, Chien-Min Kao, Hsin-Hsiung Huang
abstract
Background: Positronium lifetime imaging extends conventional positron emission tomography by using the time interval between positron emission and annihilation as an additional contrast mechanism. Voxel-wise lifetime estimation in fully three-dimensional settings is computationally difficult because the number of feasible detector-time channels grows rapidly, whereas only a small subset is observed in practice. We developed a scalable statistical framework for three-dimensional positronium lifetime estimation based on a time-of-flight-aware partial system matrix restricted to observed detector-time channels, combined with posterior event-to-voxel weighting and a conjugate Gamma--Exponential update for closed-form voxel-wise effective-rate estimation.
Results: Restricting the forward model to observed detector-time channels reduced memory and computational requirements while preserving the Poisson data model for retained detected triple coincidences. In simulated data with 4056 voxels, the analytic Bayesian estimator required 2.76 s versus 74.46 s for 10 L-BFGS-B iterations on the same CPU while accurately recovering the effective-rate map. In a triple-coincidence dataset acquired with a J-PET prototype scanner and a NEMA image-quality phantom, a 234 375-voxel effective-rate map was estimated in approximately 3 s from about 3.64×105 retained events.
Conclusions: Restricting the system matrix to observed detector-time channels makes fully three-dimensional positronium lifetime estimation computationally practical for sparse triple-coincidence data. The proposed posterior-weighted conjugate update provides a fast and stable single-component surrogate estimator of voxel-wise effective lifetime for large-scale three-dimensional positronium lifetime imaging.
Monte Carlo-Based Scatter Correction for the Plastic Based Modular PET Scanner J-PET
R. Bayerlein†, M. Das†, S. Sharma, R. D. Badawi, E. Y. Beyene, N. Chug, C. Curceanu, E. Czerwiński, K. V. Eliyan, J. Hajduga, A. Hubalewska-Dydejczyk, S. Jalali, K. Kacprzak, T. Kaplanoglu, Ł. Kapłon, K. Kasperska, A. Khreptak, G. Korcyl, T. Kozik, K. Kubat, S. K. Kundu, A. K. Venadan, D. Kumar, E. Lisowski, F. Lisowski, J. Mędrala-Sowa, S. Moyo, W. Mryka, S. Niedźwiecki, M. Opalińska, P. Pandey, A. Pandey, S. Parzych, A. Porcelli, B. Rachwał, M. Rädler, B. A. Spencer, A. Sowa-Staszczak, M. Skurzok, T. Szumlak, S. Tiwari, P. Tanty, K. T. Ardebili, E. Ł. Stępień, and P. Moskał.
†These authors contributed equally to this work.
abstract
First Positronium Lifetime Imaging using 52Mn and 55Co with a plastic-based PET scanner
M. Das, S. Sharma, E. Y. Beyene, A. Bilewicz, J. Choiński, N. Chug, C. Curceanu, E. Czerwiński, J. Hajduga, S. Jalali, K. Kacprzak, T. Kaplanoglu, Ł. Kapłon, K. Kasperska, A. Khreptak, G. Korcyl, T. Kozik, K. Kubat, D. Kumar, S. Kumar Kundu, A. Kunimmal Venadan, E. Lisowski, F. Lisowski, J. Medrala-Sowa, S. Moyo, W. Mryka, S. Niedźwiecki, A. Pandey, P. Pandey, S. Parzych, A. Porcelli, B. Rachwał, M. Rädler, N. Rathod, N. Razzaq, A. Rominger, K. Shi, M. Skurzok, M. Słotwiński, A. Stolarz, T. Szumlak, P. Tanty, K. Tayefi Ardebili, S. Tiwari, K. Valsan Eliyan, R. Walczak, E. Ł. Stępień, P. Moskal
abstract
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.
First ex-vivo positronium imaging of tissues with modular J-PET scanner using 44Sc radionuclide
K. Kubat, M. Das, S. Sharma, E. Y. Beyene, A. Bilewicz, J. Choiński, N. Chug, C. Curceanu, E. Czerwiński, J. Hajduga, S. Jalali, K. Kacprzak, T. Kaplanoglu, Ł. Kapłon, K. Kasperska, A. Khreptak, G. Korcyl, T. Kozik, D. Kumar, S. Kumar Kundu, A. Kunimmal-Venadan, B. Leszczyński, E. Lisowski, F. Lisowski, J. Mędrala-Sowa, S. Moyo, W. Mryka, S. Niedźwiecki, A. Pandey, P. Pandey, S. Parzych, A. Porcelli, B. Rachwał, M. Rädler, M. Skurzok, A. Stolarz, T. Szumlak, P. Tanty, K. Tayefi Ardebili, S. Tiwari, K. Valsan Eliyan, R. Walczak, P. Moskal, E. Ł. Stępień
abstract
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).
Towards the Development of an Iterative Algorithm for Positronium Lifetime Imaging Using 44Sc with the Modular J-PET
A. Pandey, S. Sharma, M. Das, H.-Hsiung Huang, B. Uluutku, G. Gasparato, C.-Min Kao, E. Stepien, P. Moskal
2nd Symposium on new trends in nuclear and medical physics, Krakow, Poland (24-26 September 2025)
