Fig. 1.

Multi-echo signal characterization. Panel A shows the signal decay captured in multi-echo EPI images, for a single representative volume. With longer TE, gray/white contrast increases. Susceptibility artifact (e.g. dropout) also increases, as regions near in proximity to air-tissue boundaries have shorter T2*. The T2*-weighted optimal combination (TSOC) implements a matched-filter of TE images yielding a new image with optimized gray/white contrast (TE ~ T2*) and mitigation of susceptibility artifact. Panel B shows comparisons of time series data across three regions of interest; ventromedial prefrontal cortex (vMPFC), posterior cingulate cortex/precuneus (PCC), and right cerebellum. Each comparison shows the time series before model-based filtering of the middle TE image (black), TSOC image (blue), BOLD signals isolated on the basis of TE-dependence (green), and non-BOLD signals removed from the data (red). Purple and orange lines represent modeled mentalizing and physical blocks respectively.