Quantify the impact of decreased oxygen partial pressure on ortho-positronium lifetime in living tissue

Determine the change in the mean ortho-positronium lifetime in living biological tissue resulting from a 50 mmHg decrease in oxygen partial pressure, to calibrate in vivo positronium-based hypoxia assessment.

Background

The paper reviews how ortho-positronium (o-Ps) lifetime is sensitive to oxygen concentration and free-volume structure. It compiles reported differences in oxygen partial pressure between healthy and cancer tissues (typically 10–50 mmHg) and presents experimental evidence that o-Ps lifetime decreases with increasing oxygen concentration in liquids.

While water shows relatively small lifetime changes over clinically relevant oxygen ranges, certain organic liquids exhibit much larger effects, suggesting tissue-dependent responses. However, the precise quantitative relationship for living tissues under a 50 mmHg oxygen decrease remains unmeasured, which is critical for interpreting positronium lifetime as a hypoxia biomarker in vivo.