Positronium and Quantum Entanglement Imaging: A New Trend in Positron Emission Tomography

We report on the progress in the development of positronium imaging and quantum entanglement imaging achieved thus far by the J-PET collaboration. Positronium (a bound state of electron and positron) is copiously produced in the human body during positron emission tomography. Its properties depend on the size of the intra-molecular voids and concentration in them of molecules as e.g. molecular oxygen. Therefore, positronium may serve as a biomarker of tissue pathology and hypoxia. Recently, the positronium imaging method was developed and the first positronium images of phantoms comprised of tumor cardiac myxoma and healthy adipose tissues were created by means of the J-PET tomograph. A significant difference in mean positronium lifetime in cardiac myxoma and adipose tissues opens promising perspectives for the application of positronium as a cancer diagnostic indicator. It is also important to note that photons originating from the decay of positronium are quantum entangled in polarisation. Thus, it can be hypothesized that by measuring the degree of entanglement of photons from positronium annihilation, additional information can be obtained about the molecular environment in which the positronium is formed. J-PET is the first PET system enabling the determination of linear polarisation of annihilation photons. The measurements performed with the J-PET detector confirm that the distribution of relative angle between the polarization of 511 keV back-to-back photons is consistent with the assumption that these photons are quantum entangled. These results open up prospects for the study of quantum entanglement of photons from positronium annihilation in living organisms.