Access to scanners for magnetic resonance imaging (MRI) is typically limited by cost and by infrastructure requirements. Here, we report the design and testing of a portable prototype scanner for brain MRI that uses a compact and lightweight permanent rare-earth magnet with a built-in readout field gradient. The 122-kg low-field (80 mT) magnet has a Halbach cylinder design that results in a minimal stray field and requires neither cryogenics nor external power. The built-in magnetic field gradient reduces the reliance on high-power gradient drivers, lowering the overall requirements for power and cooling, and reducing acoustic noise. Imperfections in the encoding fields are mitigated with a generalized iterative image reconstruction technique that leverages previous characterization of the field patterns. In healthy adult volunteers, the scanner can generate T1-weighted, T2-weighted and proton density-weighted brain images with a spatial resolution of 2.2 × 1.3 × 6.8 mm3. Future versions of the scanner could improve the accessibility of brain MRI at the point of care, particularly for critically ill patients.
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The MRI data were analysed using custom code in MATLAB 2018b. Image reconstruction and processing code is available from GitHub at https://github.com/czcooley/portable-MRI. Field-mapping MATLAB code and TNMR files are available from the corresponding author upon request.
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We thank T. Witzel for valuable advice over the course of developing the system, as well as specific assistance with consoles; M. Haskell for contributing to the magnet design algorithm; M. David for assistance with the gradient nonlinearity analysis; S. Sigalovsky for the construction of mechanical components; J. Conklin for insightful discussions on clinical applications; and N. Koonjoo for help with the helmet coil design. The research reported in this publication was supported by the National Institute of Biomedical Imaging and Bioengineering of the National Institutes of Health under award nos. R01EB018976, 5T32EB1680 and R00EB021349.
M.H.L. is a consultant for GE Healthcare and receives research funding from GE Healthcare. L.L.W. and S.F.C. receive research funding from Siemens Healthineers. M.S.R. is a co-founder of Hyperfine Research and receives research funding from GE Healthcare. C.Z.C., J.P.S. and L.L.W. are listed as inventors on a patent (US patent 10,359,481) filed by Partners HealthCare for portable MRI using a rotating array of permanent magnets. C.Z.C., J.P.S., B.G., M.S.R. and L.L.W. are listed as inventors on a patent (US patent application 16/092,686) filed by Partners HealthCare for the use of swept RF pulses applied with RF spatial phase gradients. C.Z.C., J.P.S. and L.L.W. are consultants and equity holders for Neuro42, Inc.
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Cooley, C.Z., McDaniel, P.C., Stockmann, J.P. et al. A portable scanner for magnetic resonance imaging of the brain. Nat Biomed Eng 5, 229–239 (2021). https://doi.org/10.1038/s41551-020-00641-5
Nature Biomedical Engineering (2021)
Nature Communications (2021)