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. 2023 Sep;1(9):617-630.
doi: 10.1038/s44222-023-00086-w. Epub 2023 Jul 17.

Brain imaging with portable low-field MRI

W Taylor Kimberly  1 , Annabel J Sorby-Adams  1 , Andrew G Webb  2 , Ed X Wu  3 , Rachel Beekman  4 , Ritvij Bowry  5 , Steven J Schiff  6 , Adam de Havenon  7 , Francis X Shen  8   9 , Gordon Sze  10 , Pamela Schaefer  11 , Juan Eugenio Iglesias  12   13   14 , Matthew S Rosen  12 , Kevin N Sheth  4
Affiliations

Brain imaging with portable low-field MRI

W Taylor Kimberly et al. Nat Rev Bioeng. 2023 Sep.

Abstract

The advent of portable, low-field MRI (LF-MRI) heralds new opportunities in neuroimaging. Low power requirements and transportability have enabled scanning outside the controlled environment of a conventional MRI suite, enhancing access to neuroimaging for indications that are not well suited to existing technologies. Maximizing the information extracted from the reduced signal-to-noise ratio of LF-MRI is crucial to developing clinically useful diagnostic images. Progress in electromagnetic noise cancellation and machine learning reconstruction algorithms from sparse k-space data as well as new approaches to image enhancement have now enabled these advancements. Coupling technological innovation with bedside imaging creates new prospects in visualizing the healthy brain and detecting acute and chronic pathological changes. Ongoing development of hardware, improvements in pulse sequences and image reconstruction, and validation of clinical utility will continue to accelerate this field. As further innovation occurs, portable LF-MRI will facilitate the democratization of MRI and create new applications not previously feasible with conventional systems.

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Conflict of interest statement

Competing interests M.S.R. is a founder and equity holder of Hyperfine Inc. W.T.K. and K.N.S. have sponsored research agreements between their respective institutions and Hyperfine Inc. All other co-authors declare no conflict of interest.

Figures

Fig. 1 |
Fig. 1 |. Types of MRI geometries for portable LF-MRI.
a, Conventional solenoid MRI. b, Biplanar permanent low-field MRI (LF-MRI), including C-arm and H-arm geometries. c, Halbach array LF-MRI configuration. B0, main magnetic field; B1, radiofrequency field; RF, radiofrequency. Part a, upper panel, image courtesy of National High Magnetic Field Laboratory. Part a, bottom panel, adapted with permission from ref., IEEE. Part b, upper panel, adapted from ref., CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Part b, bottom panel, adapted with permission from ref., Wiley. Part c upper panel © [2018] IEEE. Reprinted, with permission, from Cooley, C. Z., Haskell, M. W., Cauley, S. F., Sappo, C., Lapierre, C. D., Ha, C. G., Stockmann, J. P. & Wald, L. L. Design of sparse Halbach magnet arrays for portable MRI using a genetic algorithm. IEEE Trans. Magn. 54, 5100112 (2018). Adaptation permission from author. Part c, bottom panel, adapted with permission from ref., iMRI.
Fig. 2 |
Fig. 2 |. Examples of images acquired on LF-MRI compared with conventional HF-MRI.
Clinical applications for low-field MRI (LF-MRI) include acute ischaemic stroke (diffusion-weighted imaging), intracerebral haemorrhage (T2 fluid-attenuated inversion recovery), cardiac arrest (T1-weighted imaging), paediatric hydrocephalus (T2-weighted imaging), and white matter hyperintensity (fluid- attenuated inversion recovery). Note the previously undetected region of ischaemia on LF-MRI diffusion-weighted imaging that was not detected on high-field MRI (HF-MRI) performed 3 days prior. All images were acquired on a 0.064 T portable LF-MRI (Hyperfine Research Inc.). HF-MRI and LF-MRI images of acute ischaemic stroke were adapted/reprinted from Science Advances ref.. ©The Authors, some rights reserved; exclusive licensee AAAS. HF-MRI and LFMRI images of intracerebral haemorrhage reprinted from ref., Springer Nature Limited. HF-MRI and LF-MRI images of cardiac arrest reprinted with permission from ref., Elsevier. HF-MRI and LF-MRI images of paediatric hydrocephalus reproduced from ref. with permission from BMJ Publishing Group Ltd. HF-MRI and LF-MRI images of white matter hyperintensity were reprinted from ref., CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/).
Fig. 3 |
Fig. 3 |. The evolution of LF-MR neuroimaging.
In the early 1980s, MR magnets operated in the low-field (LF) range. The inherent reduced signal-to-noise ratio facilitated development of higher-field systems, with the perception in the scientific community that higher static field strength equated to better performance. Despite several advances in the 1990s, the turn of the millennium saw a renaissance of LF-MRI. The first FDA-approved device was deployed in 2020 and, since 2021, LF-MRI at 0.064 T has been investigated in a range of conditions and environments. As LF-MRI continues to evolve, bioengineers will play an increasing role in its future. AUTOMAP, end-to-end deep neural network approach; SQUID, superconducting quantum interference device–.
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