Hypoxia imaging with the nitroimidazole 18F-FAZA PET tracer: A comparison with Oxylite, EPR Oximetry and 19F-MRI Relaxometry

Background and purpose: 18F-FAZA is a nitroimidazole PET tracer that can provide images of tumor hypoxia. However, it cannot provide absolute pO 2 values. To qualify 18F-FAZA PET, we compared PET images to pO 2 measured by OxyLite, EPR oximetry and 19F-MRI. Materials and methods: Male WAG/Rij rats grafted with rhabdomyosarcoma were used. Tumor oxygenation was modified by gas breathing (air or carbogen). The same day of PET acquisition, the pO 2 was measured in the same tumor either by OxyLite probes (measurement at 10 different sites), EPR oximetry using low frequency EPR or 19F-relaxometry using 15C5 on an 11.7 T MR system. Results: There was a good correlation between the results obtained by PET and EPR (R = 0.93). In the case of OxyLite, although a weaker correlation was observed (R = 0.55), the trend for two values to agree was still related to the inverse function theoretically predicted. For the comparison of 18F-FAZA PET and 19F-MRI, no change in T 1 was observed. Conclusions: A clear correlation between 18F-FAZA PET image intensities and tumor oxygenation was demonstrated, suggesting that 18F-FAZA PET is a promising imaging technique to guide cancer therapy. © 2011 Elsevier Ireland Ltd. All rights reserved.