Changes in oxygenation of intracranial tumors with carbogen: a BOLD MRI and EPR oximetry study

Purpose: To examine, using blood oxygen level dependent (BOLD) MRI and EPR oximetry, the changes in oxygenation of intracranial tumors induced by carbogen breathing. Materials and Methods: The 9L and CNS-1 intracranial rat tumor models were imaged at 7T, before and during carbogen breathing, using a multi-echo gradient echo (GE) sequence to map R-2*. On a different group of 9L tumors, tissue pO(2) was measured using EPR oximetry with lithium phthalocyanine as the oxygen-sensitive material. Results: The average decline in R-2* with carbogen breathing was 13 +/- 1 s(-1) in the CNS-1 tumors and 29 +/- 4 s(-1) in the 9L tumor. The SI vs. TE decay curves indicate the presence of multiple components in the tumor. Tissue pO(2) in the two 9L tumors measured was 8.6 +/- 0.5 and 3.6 +/- 0.6 mmHg during air breathing and rose to 20 +/- 7 and 16 +/- 4 mmHg (mean +/- SE) with carbogen breathing. Significant changes were observed by 10 minutes, but changes in pO(2) and R-2* continued in some subjects over the entire 40 minutes. Conclusion: EPR results indicate that glial sarcomas may be radiobiologically hypoxic. Both EPR and BOLD data indicate that carbogen breathing increases brain tumor oxygenation. These data support the use of BOLD imaging to monitor changes in oxygenation in brain tumors.