Motion compensated structured low‐rank reconstruction for 3D multi‐shot EPI

Abstract Purpose The 3D multi‐shot EPI imaging offers several benefits including higher SNR and high isotropic resolution compared to 2D single shot EPI. However, it suffers from shot‐to‐shot inconsistencies arising from physiologically induced phase variations and bulk motion. This work proposed a motion compensated structured low‐rank (mcSLR) reconstruction method to address both issues for 3D multi‐shot EPI. Methods Structured low‐rank reconstruction has been successfully used in previous work to deal with inter‐shot phase variations for 3D multi‐shot EPI imaging. It circumvents the estimation of phase variations by reconstructing an individual image for each phase state which are then sum‐of‐squares combined, exploiting their linear interdependency encoded in structured low‐rank constraints. However, structured low‐rank constraints become less effective in the presence of inter‐shot motion, which corrupts image magnitude consistency and invalidates the linear relationship between shots. Thus, this work jointly models inter‐shot phase variations and motion corruptions by incorporating rigid motion compensation for structured low‐rank reconstruction, where motion estimates are obtained in a fully data‐driven way without relying on external hardware or imaging navigators. Results Simulation and in vivo experiments at 7T have demonstrated that the mcSLR method can effectively reduce image artifacts and improve the robustness of 3D multi‐shot EPI, outperforming existing methods which only address inter‐shot phase variations or motion, but not both. Conclusion The proposed mcSLR reconstruction compensates for rigid motion, and thus improves the validity of structured low‐rank constraints, resulting in improved robustness of 3D multi‐shot EPI to both inter‐shot motion and phase variations.