LAUSR

Introduction Geometric distortions along the phase encode direction caused by off‐resonant spins are still a major issue in EPI based functional and diffusion imaging. If the off‐resonance map is known it is possible to correct for distortions. Most correction methods operate as a post‐processing step on the reconstructed magnitude images. Theory and methods Here, we present an algebraic reconstruction method (hybrid‐space SENSE) that incorporates a physics based model of off‐resonances, phase inconsistencies between k‐space segments, and T2*‐decay during the acquisition. The method can be used to perform a joint reconstruction of interleaved acquisitions with normal (blip‐up) and inverted (blip‐down) phase encode direction which results in reduced g‐factor penalty. Results A joint blip‐up/down simultaneous multi slice (SMS) reconstruction for SMS‐factor 4 in combination with twofold in‐plane acceleration leads to a factor of two decrease in maximum g‐factor penalty while providing off‐resonance and eddy‐current corrected images. Conclusion We provide an algebraic framework for reconstructing diffusion weighted EPI data that in addition to the general applicability of hybrid‐space SENSE to 2D‐EPI, SMS‐EPI and 3D‐EPI with arbitrary k‐space coverage along z, allows for a modeling of arbitrary spatio‐temporal effects during the acquisition period like off‐resonances, phase inconsistencies and T2*‐decay. The most immediate benefit is a reduction in g‐factor penalty if an interleaved blip‐up/down acquisition strategy is chosen which facilitates eddy current estimation and ensures no loss in k‐space encoding in regions with strong off‐resonance gradients. HighlightsAn algebraic off‐resonance corrected reconstruction for EPI acquisition is proposed.The extended hybrid‐space SENSE reconstruction handles 2D, SMS‐EPI and 3D‐EPI acquisitions.Allows to account for off‐resonances and eddy‐currents and dynamic phase changes between segments.Joint interleaved blip up/down reconstruction leads to significantly reduced g‐factor penalty.