Quantification of radicals in aqueous solution by positronium lifetime; An Experiment using a clinical PET scanner

Takyu, Sodai*; Matsumoto, Kenichiro*; Hirade, Tetsuya  ; Nishikido, Fumihiko*; Akamatsu, Go*; Tashima, Hideaki*; Takahashi, Miwako*; Yamaya, Taiga*

Positrons and electrons sometimes exist as a bound state, positronium (Ps), in living organisms. The triplet Ps (ortho-Ps) annihilation time represents the ortho-Ps pick-off annihilation lifetime, and it varies depending on the surrounding electron density. The ortho-Ps lifetime may add new biological information to PET scan information. In order to discuss the feasibility of quantifying (free) radicals in vivo by the ortho-Ps lifetime, we used a clinical PET system to make ortho-Ps lifetime measurements in aqueous solutions containing radicals. The results suggested that differences in radical concentrations in aqueous solutions of the order of a few mM could be quantified by the ortho-Ps lifetime if the counting statistic of the positron annihilation events was more than 10 events. This concentration was higher than the radical concentration generated in the physiological functions of living organisms.