Tumor oxygen dynamics: Comparison of ¹⁹F MR EPI and frequency domain NIR spectroscopy

Oxygen plays a key role in tumor therapy and may be related to tumor development: e.g., angiogenesis and metastasis. Using noninvasive techniques to accurately measure tumor oxygenation could assist in developing novel therapies. Here, we have used the FREDOM (Fluorocarbon Relaxometry using Echo planar imaging for Dynamic Oxygen Mapping) approach based on hexafluorobenzene (HFB) to monitor tissue oxygen tension (pO₂) of rat breast and prostate tumors and compared the results with changes in tumor vascular hemoglobin saturation (sO₂) and concentration observed using a new dual wavelength homodyne near-infrared (NIR) system. The dynamic changes in pO ₂ and sO₂ were assessed while rats were breathing various gases. NIR showed significant changes in vascular oxygenation accompanying respiratory interventions. ¹⁹F MR-EPI also showed significant changes in tissue pO₂ and revealed considerable regional heterogeneity in both absolute values and rate of change accompanying interventions. Generally, changes in vascular sO₂ preceded tissue pO₂, particularly for smaller tumors.