Figure 3.

MCFLIRT realignment parameters. Figure illustrates realignment (motion) parameters reported by MCFLIRT for a representative ex-33-week premature infant scanned at 4-weeks corrected age (2.75 months postnatal age). Results are summarized in three graphs, providing an index of head position throughout the scan for each volume in the time-series (x-axis; 280 total volumes). Estimated rotation (in radians; A) and translation (in millimeters; B) parameters are described with respect to each axis (x, y, z). In panel (C), aforementioned parameters are condensed by MCFLIRT into a single vector referred to as root mean squared (RMS) displacement (in millimeters), which summarizes cumulative motion in terms of absolute and relative measures. Absolute RMS displacement (blue) describes motion in a given volume with respect to a reference time point (i.e., middle volume in time-series), providing useful information on gradual shifts in head position over time. Relative RMS displacement (green) at a given volume describes motion with respect to the subsequent time point, useful for identifying abrupt changes in head position. Gray regions highlight initial 28 volumes in time-series that contain excessive motion (e.g., spikes >2.5 mm absolute or >0.25 mm relative displacements), surpassing established parameter criteria for inclusion. Importantly, gray region extends beyond obvious jump in relative displacement to include steep declining slope in absolute displacement. This is to address residual effects of motion that often extend beyond apparent spikes in relative displacement (51). These volumes are removed via data scrubbing (see Data Scrubbing in Section “Preprocessing”). Panel (D) shows RMS displacement (cumulative motion) realignment parameters after data scrubbing. Reduction in total number of volumes from 280 to 252 (red arrows) reflects removal of initial 28 volumes (gray regions removed). Note attenuated motion parameters (y-axis; green) throughout scan. Importantly, relative displacement, remains below threshold criteria for duration of scan (red dashed line). Mean RMS displacements of original time-series (absolute, 1.05 mm; relative, 0.13 mm) are greatly reduced by data scrubbing (absolute, 0.58 mm; relative, 0.03 mm).