Inherent Geometry Correction for Diffusion EPI Using the Reference Echoes as Navigators
Figure 2
Simulations of the geometry correction using the time-dependent phase from the nonphase–encoded EPI reference scan. A 1-dimensional numerical phantom along the phase-encode direction is used, containing 3 fractions: fat rims, central composite water/fat, and a local intense water compartment with additional frequency offset. Simulations show the effect of phase correction without (a) and with (b) fat suppression for the phase correction vectors. The black solid line represents the numerical phantom, the blue dashed line represents the state-of-the-art EPI reconstruction, and the red and green solid lines shows the reconstruction where each echo is corrected with the nonphase–encoded navigator echo at the corresponding time point in the EPI train. Correction for the fat-suppressed image data is shown in (c). The sensitivity of the correction to residual fat signal is evaluated in (d) for 0% (black), 20% (green), 40% (blue), and 60% (red) residual fat signal in navigator and image.