Reproducibility of Volumetric Analysis using Ultra-Low-Field Portable Magnetic Resonance Imaging

Brain volume change over time is an important imaging-based biomarker of disease. However, traditional MR scanners are associated with high direct and indirect costs both up front and over time, rendering them inaccessible to many around the world. Recently, ultra-low-field (64 mT) portable MR scanners have been introduced for clinical use and have been highly safe and informative for neurologic monitoring. Volumetrics present an important potential use for ultra-low-field MRI that has yet to be established. The aim of the present work was to examine qualitative similarities between volume measurements in adults and to address the questions of reproducibility through test-retest reliability and external validity using recent software updates to the Hyperfine Swoop system, versions 8.8.1 and 9.0.0. In twenty neurologically typical adults, structural volumes demonstrated high test-retest intraclass correlations regardless of software (>0.999-0.883). Regional intraclass correlations also were explored, with the lowest stability observed in structures that were relatively central and caudal, though more recent software provided relative improvements. Regardless of field strength or software, measurements were comparable to those established in growth charts. These findings constitute a crucial foundation for the clinical utility of 64 mT MRI in monitoring brain volume loss over time.