Fig. 1

Pictorial representation of the single detection ring of the positron emission tomography scanner and (not to scale) magnified part of the hemoglobin molecule with pictorial representation of the possible ways of decays of positronium atoms (Ps) trapped in the intramolecular voids. Left-upper (black arrows) and right-upper (red arrows) indicate annihilations in the space free of electrons for para-positronium and ortho-positronium, respectively. Annihilation of positronium through the interaction with the electron from the surrounding molecule is shown in the left-lower corner (violet arrows) while in the right-lower part the conversion of ortho-positronium into para-positronium via interaction with the oxygen molecule and subsequent decay of para-positronium to two photons (magenta arrows) are presented [7]