The residual variance after single regressor regressions for 2D GRE-EPI (a), 3D GRE-EPI (b), non-synchronized SPGR (c), synchronized SPGR (d), non-synchronized bSSFP (e), and synchronized bSSFP (f). RetroICor results are shown in red and RetroKCor results are shown in black. The mean across subjects is plotted with the error bars representing the standard deviation. The dashed gray line represents the expected residual variance obtained by a regression with a randomly constructed regressor.