J-PET is a multi-photon PET system prototype  enabling multi-photon and positronium imaging. The quality of these images relies strongly on the system's time resolution. In this presentation, we will explain the newly developed method of positronium imaging and present the first multi-photon  and in-vitro positronium images . We will discuss the clinical motivation for improving the system time resolution and present arguments demonstrating that the high sensitivity and high time-resolution multi-photon total-body PET systems  open realistic perspectives for the application of positronium as a biomarker for in-vivo assessment of the tissue pathology and the degree of hypoxia .
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