Regional Tumor Oxygenation and Measurement of Dynamic Changes

We recently described a novel approach to measuring regional tumor oxygen tension using 19 F pulse burst saturation recovery (PBSR) nuclear magnetic resonance (NMR) echo planar imaging (EPI) relaxometry of hexafluorobenzene. We now compare oxygen tension measurements in a group of size-matched R3327-AT1 Dunning prostate rat tumors made using this new method with those using a traditional polarographic method: the Eppendorf histograph. Similar oxygen tension distributions were found using the two methods, and both techniques showed that tumors with volume greater than $3.5\ {\rm cm}^{3}$ were significantly (P < 0.0001) less well oxygenated than smaller tumors (volume less than $2\ {\rm cm}^{3}$). Using the 19 F EPI approach, we also examined the response to respiratory challenge. Increasing the concentration of inspired oxygen from 33% to 100% O2 produced a significant increase (P < 0.0001) in tumor oxygenation for a group of small tumors. In contrast, no change was observed in the mean $p{\rm O}_{2}$ for a group of large tumors. Consideration of individual tumor regions irrespective of tumor size showed a strong correlation between the maximum $p{\rm O}_{2}$ observed when breathing 100% O2 compared with mean baseline $p{\rm O}_{2}$. These results further demonstrate the usefulness of 19 F EPI to assess changes in regional tumor oxygenation.