Deep tissue pO2 measurement by a diffuse optical lifetime detection technology

Tissue oxygenation is a key physiological parameter reflecting cellular metabolism and tissue viability. Accurate, noninvasive quantification of partial oxygen pressure (pO2) in deep tissues is essential for preclinical small -animal studies but remains challenging due to the invasiveness, limited depth sensitivity, or poor temporal resolution of existing methods. We developed a fiber-based diffuse phosphorescence lifetime detection system for real-time, quantitative, and noninvasive measurement of tissue oxygenation at varying depths. The system employs an oxygen-sensitive phosphorescent probe and time-resolved lifetime detection, exploiting the inverse relationship between phosphorescence lifetime and local oxygen concentration due to dynamic quenching. Depth sensitivity is achieved by varying the source–detector separation on the tissue surface to modulate photon sampling depth. In a small-animal model, a 0 mm source–detector separation predominantly sampled superficial tissue, yielding an oxygen tension of approximately 15 mmHg. Increasing the separation to 5 mm enabled deeper interrogation of muscle tissue, where pO₂ increased to approximately 25 mmHg. Greater separations resulted in reduced signal intensity and increased variability due to tissue scattering and absorption. These results demonstrate that fiber-based diffuse phosphorescence lifetime detection enables depth-resolved, noninvasive measurement of tissue oxygenation in vivo and provides a practical tool for monitoring dynamic oxygenation changes in preclinical models.