In-vivo correction of B0-induced distortions in a portable Halbach scanner

Motivation: Permanent, Halbach-based magnets are suitable for lightweight and affordable scanners for brain and musculoskeletal imaging. Unfortunately, they tend to suffer from poor B0 homogeneity, creating distortions that compromise standard reconstructions. Goal(s): We aim to evaluate the performance of a new approach for distortion correction in-vivo in a 90 mT Halbach system. Approach: We employ a single-point double-shot (SPDS) sequence prior to the acquisition to map the magnetic field in an undistorted image space. This information is included in an Encoding Matrix and images result from applying algebraic reconstruction techniques (ART). Results: Model-based reconstructions after SPDS surpass the quality of standard reconstruction methods. Impact: The value of brain and musculoskeletal images obtained in low-cost scanners can be significantly enhanced with respect to standard methods when the main magnetic field deviates substantially from an ideal, homogeneous distribution.