MRI measurements correctly predict the relative effects of tumor oxygenating agents on hypoxic fraction in rodent BA1112 tumors

Purpose: We evaluate whether magnetic resonance imaging (MRI) with blood ox ygenation level-dependent (BOLD) contrast correctly predicts the relative e ffects of tumor-oxygenating agents on hypoxic fraction in BA1112 rhabdomyos arcomas in WAG/Rij rats. Methods and materials: The response of ten tumors to carbogen (95% O-2/5% C O2), a perfluorocarbon emulsion (PFC), and the combination of PFC + carboge n was studied with high spectral and spatial resolution MR imaging of the w ater resonance at 4.7 Tesla. Decreases in MR signal linewidth indicate incr eases in tumor blood oxygen levels. Results: Average MR signal linewidth was decreased 2.0% by carbogen, 2.5% b y PFC + air, and 4.9% by PFC + carbogen. PFC + carbogen caused a larger lin ewidth decrease than either treatment alone (p < 0.04 by ANOVA). Maps of pi xels responding to treatment indicate that combining PFC with carbogen sign ificantly enlarges the area of the tumor in which oxygen levels are increas ed (p < 0.01 by ANOVA). Conclusion: MRI predicts that PFC + carbogen will increase radiosensitivity more than either treatment alone; this agrees with the known effects of th ese treatments on hypoxic fraction. Utilizing MRI to choose the treatment t hat maximizes the size and extent of increases in tumor oxygenation could r educe hypoxic fraction. (C) 2000 Elsevier Science Inc.