Interpreting Resting-State fMRI activity across echo times (TEs)

BOLD signals acquired with multi-echo fMRI contain different contrasts across echo times (TEs). Empirical research suggests that the signal information from these different contrasts are possibly biologically distinct from early to long echo times. In EPTI, high-frequency signals observed at earlier echo times may indicate more structural or localized information, due to tissue-bound fluids with shorter T2* decay. Low-frequency signals at longer echo times may indicate vascular or wide-spread functional information, due to more free-flowing fluids with longer T2* decay. We propose examination of the signal evolution of fMRI across echo times (TEs), through utilization of dynamic functional connectivity (dFNC) and a modified bi-exponential decay model. This study provides novel information to the multi-echo field on evolving dynamic state-based signal connectivity occurring across echo times.