Real-time electrochemical monitoring of brain tissue oxygen: A surrogate for functional magnetic resonance imaging in rodents

Long-term in-vivo electrochemistry (LIVE) enables real-time monitoring and measurement of brain metabolites. In this study we have simultaneously obtained blood oxygenation level dependent (BOLD) fMRI and amperometric tissue O2 data from rat cerebral cortex, during both increases and decreases in inspired O2 content. BOLD and tissue O2 measurements demonstrated close correlation (r = 0.7898) during complete (0%) O2 removal, with marked negative responses occurring ca. 30 s after the onset of O2 removal. Conversely, when the inspired O2 was increased (50, 70 and 100% O2 for 1 min) similar positive rapid changes (ca. 15 s) in both the BOLD and tissue O2 signals were observed. These findings demonstrate, for the first time, the practical feasibility of obtaining real-time metabolite information during fMRI acquisition, and that tissue O2 concentration monitored using an O2 sensor can serve as an index of changes in the magnitude of the BOLD response. As LIVE O2 sensors can be used in awake animals performing specific behavioural tasks the technique provides a viable animal surrogate of human fMRI experimentation.