First Positronium Lifetime Imaging with Scandium-44 on a Long Axial Field-of-view PET/CT

Lorenzo Mercolli; William M. Steinberger; Pascal V. Grundler; Anzhelika Moiseeva; Saverio Braccini; Maurizio Conti; Paweł Moskal; Narendra Rathod; Axel Rominger; Hasan Sari; Roger Schibli; Robert Seifert; Kuangyu Shi; Ewa Ł. Stępień; Nicholas P. van der Meulen

arXiv · 2506.13460

First Positronium Lifetime Imaging with Scandium-44 on a Long Axial Field-of-view PET/CT

Lorenzo Mercolli·William M. Steinberger·Pascal V. Grundler·Anzhelika Moiseeva·Saverio Braccini·Maurizio Conti·Paweł Moskal·Narendra Rathod·Axel Rominger·Hasan Sari·Roger Schibli·Robert Seifert·Kuangyu Shi·Ewa Ł. Stępień·Nicholas P. van der Meulen

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Abstract

Purpose: 44Sc has been successfully produced, synthesized, labeled and first-in-human studies were conducted some years ago. The decay properties of 44Sc, together with being close to a clinical implementation, make it an ideal candidate for in vivo positronium lifetime measurements. In this study, we investigate the count statistics for ortho-positronium (oPs) measurements with 44Sc. Method: A NEMA image quality phantom was filled with 41.7 MBq of 44Sc dissolved in water and scanned on a commercial long-axial field-of-view PET/CT. Three-photon events were identified using a prototype feature of the scanner and dedicated software. The lifetime of oPs was determined in the phantom spheres and in 4x4x4 mm^3 voxels. Results: All measured oPs lifetimes are compatible, within the uncertainties, with the literature values for water. The oPs lifetime is 2.65+-0.50, 1.39+-0.20 and 1.76+-0.18 ns in the three smallest spheres of the phantom and 1.79+-0.57 ns for a single voxel in the central region of the largest sphere. The relative standard deviation in the background regions of the time difference distributions, i.e., for time differences smaller than -2.7 ns, is above 20% - even for voxels inside the phantom spheres. Conclusions: Despite the favorable physical properties of 44Sc, the count statistics of three-photon events remains a challenge. The high prompt-photon energy causes a significant amount of random three-photon coincidences with the given methodology and, therefore, increases the statistical uncertainties on the measured oPs lifetime.

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Lorenzo Mercolli, William M. Steinberger, Pascal V. Grundler, Anzhelika Moiseeva, Saverio Braccini, Maurizio Conti, Paweł Moskal, Narendra Rathod, Axel Rominger, Hasan Sari, Roger Schibli, Robert Seifert, Kuangyu Shi, Ewa Ł. Stępień, Nicholas P. van der Meulen. 2025-06-16. First Positronium Lifetime Imaging with Scandium-44 on a Long Axial Field-of-view PET/CT. https://arxiv.org/abs/2506.13460

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