Previously we have reported that fluctuations in fMRI signals at approximately 0.1Hz are highly correlated with blood pressure fluctuations at the same frequency. A multi-echo resting-state fMRI experiment was performed at 7T to separate the effect of changes in transverse relaxation (R2*) and longitudinal magnetisation (S0) in these fluctuations. We demonstrate that the magnitudes of correlations with blood pressure are significantly greater for R2* signals, compared with corresponding S0 signals. These data suggest that there is a significant proportion of BOLD dependent signal variance in fMRI that is of non-neuronal origin.
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