Multi-Shot Multi-Echo xSPEN Technique for Portable Low-Field MRI Systems

In compact portable low-field MRI systems, imaging suffers from severe distortions due to significant field inhomogeneity and gradient nonlinearity. The purpose of this work was to develop and evaluate a Multi-Shot Multi-Echo cross-term Spatiotemporal Encoding (MS-ME xSPEN) sequence for highly compact, portable low-field MRI systems. This method aims to improve imaging performance while preserving the robustness of xSPEN to severe field inhomogeneities. The MS-ME xSPEN sequence was implemented using two image-domain multi-shot sampling techniques: segmented and interleaved. For subsequent evaluations, the segmented MS-ME xSPEN approach was selected and compared with conventional single-shot xSPEN. All experiments were performed on a 110-mT portable MRI system equipped with three gradient axes. A constant gradient environment was emulated by continuously activating a single gradient axis throughout the sequence. Imaging was performed on phantoms and in the human brain. MS-ME xSPEN exhibited superior resilience to in-plane distortions from field inhomogeneities and achieved higher SNR compared with the standard xSPEN. MS-ME xSPEN also enabled a wider range of T2-weighted contrasts. MS-ME xSPEN is well suited for compact portable MRI systems, offering improved SNR, flexible contrast, and robustness to field inhomogeneity.