Scout-based Multi-Echo NAvigator (SMENA) for high temporal resolution motion and B ₀ estimation and correction:...

To develop a data-driven technique, Scout-based Multi-Echo NAvigator (SMENA), for joint estimation of motion and B ₀ inhomogeneity ( δ B ₀ ) at a temporal resolution of ∼200 ms with minimal additional scan time for gradient-echo acquisition.

SMENA consists of two key acquisition components: SMENA-scout and SMENA-nav. SMENA-scout is a rapid 3D 4-mm multi-echo acquisition completed in less than 8 seconds, providing images with matched contrast and phase at multiple echo times. SMENA-nav captures signal variations induced by motion and δ B ₀ during the scan using compact multi-echo navigator trajectories (3.5 ms) embedded within each TR. Motion and δ B ₀ maps were jointly estimated every ∼200 ms through a model-based optimization framework relating SMENA-scout to SMENA-nav. The estimation accuracy and correction performance of SMENA were evaluated in simulations and in vivo using multi-echo GRE and GRE-EPTI acquisitions. Multiple prospective motion experiments, including large continuous movement and deep breathing, were investigated.

In both simulations and in vivo experiments, accurate motion and δ B ₀ estimation were achieved. Compared with motion-only estimation, joint estimation reduced rotation and translation errors. Joint motion and δ B ₀ correction resulted in substantial improvements in image quality, particularly at longer echo times, producing an NRMSE of 10.4% compared to 31.6% with motion-only correction. High-temporal-resolution tracking of motion and δ B ₀ enabled improved reconstruction quality in scenarios involving continuous motion and deep breathing.

SMENA enables high-temporal-resolution joint estimation of motion and δ B ₀ with minimal additional acquisition cost, providing a practical solution for motion- and δ B ₀ -robust MRI.