Non-uniform tumor vascular oxygen dynamics monitored by three-channel near-infrared spectroscopy

In a previous report, we showed that there was distinct heterogeneity in tumor oxygenation dynamics even within the same tumor monitored by ¹⁹F MR pO ₂ mapping and near-infrared spectroscopy (NIRS). In this study, we applied a three-channel NIRS system to reveal dynamic heterogeneity of tumor vascular oxygenation during respiratory challenges. When the implanted tumors reached ∼3 cm, three photo detectors were attached to the surface of the tumor in three different positions to measure changes in oxygenated hemoglobin concentration ([HbO ₂]), while the inhaled gas was alternated between air and carbogen (95% O ₂ + 5% CO ₂). Significant changes in tumor oxygenation were observed at all three detectors accompanying the respiratory challenge, and these changes could be modeled with two exponential components with fast and slow time constants. Time constant, amplitude, vascular coefficient, and the ratio of perfusion rate were obtained from fitting curves of Δ[HbO ₂]. These parameters revealed that there were indeed different responses of tumor vascular oxygenation during carbogen inhalation at the three different locations. These results clearly reveal that tumors are highly heterogeneous during vascular oxygenation in response to carbogen inhalation. This study demonstrates that the NIR technology can provide an efficient, real-time, non-invasive way for monitoring tumor physiology, and it may have prognostic value, providing insight into tumor vascular development and angiogenesis.