Tumor oximetry: Demonstration of an enhanced dynamic mapping procedure using fluorine-19 echo planar magnetic resonance imaging in the Dunning prostate R3327-AT1 rat tumor

Purpose: We have developed an enhanced approach to measuring regional oxygen tension (pO₂) dynamics in tumors. The technique is demonstrated in a group of 8 Dunning prostate rat tumors (R3327-AT1) with respect to respiratory challenge. Methods and Materials: Hexafluorobenzene was injected directly into the tumors of anesthetized rats. ¹⁹F nuclear magnetic resonance echo planar imaging relaxometry was performed to obtain maps of regional tumor oxygenation under baseline conditions and when the inhaled gas was changed to oxygen or carbogen. Results: Sequential pO₂ maps required 8 min, with a typical precision of 1-3 torr at 30-100 individual regions across a tumor. When rats breathed 33% oxygen, distinct heterogeneity was observed for baseline oxygenation in each tumor with pO₂ values ranging from hypoxic to greater than 100 torr. Larger tumors showed significantly lower baseline pO₂. Respiratory challenge with oxygen or carbogen produced significant increases in tumor oxygenation with a close correlation between the response to each gas at individual locations. Regions of both small and large tumors responded to respiratory challenge, but the rate was generally much faster in initially well-oxygenated regions. Conclusions: Regional pO₂ was assessed quantitatively and the response of multiple individual tumor regions observed simultaneously with respect to interventions.