Positrons are commonly utilized in positron emission tomography (PET) to reconstruct the biodistribution of radio-labeled molecules, revealing the localization of specific biological functions in the body. Beyond direct annihilation, the meta-stable e+/e- bound state positronium, consisting of para-Positronium (p-Ps) and ortho-Positronium (o-Ps), offers additional information, with o-Ps being sensitive to the surrounding medium's characteristics. Traditional 2γ PET lacks access o-Ps lifetime measurements, requiring a change to (β+,γ) isotopes. Shifting to o-Ps lifetime imaging in PET requires overcoming many challenges, the lower efficiency of detecting triple coincidence events implies low event rates, new radiotracers are required to accomodate the (β+,γ) isotopes, and new reconstruction algorithms need to be developed. But perhaps the most challenging part will be to know what o-Ps lifetime differences between tissues to expect and what is measurable in practice, with lifetime differences similar to current scanner time resolutions. Studies are still required to understand the evolution of o-Ps with various pathologies to assertain the interest of o-Ps lifetime imaging for clinical diagnosis. In this seminar, I will cover the challenges and the potential advantages of using positronium lifetime in imaging and for clinical diagnostics, I will also present prototypes that will allow to address the major issues.
