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A portable scanner for magnetic resonance imaging of the brain


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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Fig. 1: Portable MRI brain scanner prototype.
Fig. 2: Permanent low-field magnet design.
Fig. 3: Gradient coil design.
Fig. 4: MRI pulse sequence diagram.
Fig. 5: 3D T2-, T1- and proton density-weighted images of the brain in healthy adult volunteers.
Fig. 6: Analysis of the measured encoding field maps (Gx, Gz and Gy) in the central field map slices.

Data availability

The main data supporting the results of this study are available within the paper and its Supplementary Information. All reconstructed MATLAB image files and one exemplary raw dataset are available from GitHub at

Code availability

The MRI data were analysed using custom code in MATLAB 2018b. Image reconstruction and processing code is available from GitHub at Field-mapping MATLAB code and TNMR files are available from the corresponding author upon request.


  1. 1.

    GBD 2016 Neurology Collaborators. Global, regional, and national burden of neurological disorders, 1990–2016: a systematic analysis for the Global Burden of Disease Study 2016. Lancet Neurol. 18, 459–480 (2019).

  2. 2.

    Sánchez, Y. et al. Magnetic resonance imaging utilization in an emergency department observation unit. West J. Emerg. Med. 18, 780–784 (2017).

    PubMed  PubMed Central  Google Scholar 

  3. 3.

    Beckmann, U., Gillies, D. M., Berenholtz, S. M., Wu, A. W. & Pronovost, P. Incidents relating to the intra-hospital transfer of critically ill patients. Intensive Care Med. 30, 1579–1585 (2004).

    PubMed  Google Scholar 

  4. 4.

    Mathur, A. M., Neil, J. J., McKinstry, R. C. & Inder, T. E. Transport, monitoring, and successful brain MR imaging in unsedated neonates. Pediatr. Radiol. 38, 260–264 (2008).

    PubMed  Google Scholar 

  5. 5.

    Warf, B. C. & East African Neurosurgical Research Collaboration. Pediatric hydrocephalus in East Africa: prevalence, causes, treatments, and strategies for the future. World Neurosurg. 73, 296–300 (2010).

  6. 6.

    Wald, L. L., McDaniel, P. C., Witzel, T., Stockmann, J. P. & Cooley, C. Z. Low-cost and portable MRI. J. Magn. Reson. Imaging 52, 686–696 (2020).

    PubMed  Google Scholar 

  7. 7.

    Geethanath, S. & Vaughan, J. T. Accessible magnetic resonance imaging: a review. J. Magn. Reson. Imaging 49, e65–e77 (2019).

    PubMed  Google Scholar 

  8. 8.

    Campbell-Washburn, A. E. et al. Opportunities in interventional and diagnostic imaging by using high-performance low-field-strength MRI. Radiology 293, 384–393 (2019).

    PubMed  PubMed Central  Google Scholar 

  9. 9.

    Foo, T. K. F. et al. Lightweight, compact, and high-performance 3T MR system for imaging the brain and extremities. Magn. Reson. Med. 80, 2232–2245 (2018).

    CAS  PubMed  PubMed Central  Google Scholar 

  10. 10.

    Matter, N. I. et al. Three-dimensional prepolarized magnetic resonance imaging using rapid acquisition with relaxation enhancement. Magn. Reson. Med. 56, 1085–1095 (2006).

    PubMed  Google Scholar 

  11. 11.

    Espy, M. A. et al. Progress toward a deployable SQUID-based ultra-low field MRI system for anatomical imaging. IEEE Trans. Appl. Supercond. 25, 1–5 (2015).

    Google Scholar 

  12. 12.

    Sarracanie, M. et al. Low-cost high-performance MRI. Sci. Rep. 5, 15177 (2015).

    CAS  PubMed  PubMed Central  Google Scholar 

  13. 13.

    Vaughan, J. T. et al. Progress toward a portable MRI system for human brain imaging. Proc. Intl Soc. Mag. Reson. Med. 24, 0498 (2016).

    Google Scholar 

  14. 14.

    Cooley, C. Z. et al. Design of sparse Halbach magnet arrays for portable MRI using a genetic algorithm. IEEE Trans. Magn. 54, 1–12 (2018).

    Google Scholar 

  15. 15.

    O’Reilly, T., Teeuwisse, W., Winter, L. & Webb, A. G. The design of a homogenous large-bore Halbach array for low field MRI. Proc. Intl Soc. Mag. Reson. Med. 27, 0272 (2019).

    Google Scholar 

  16. 16.

    Ren, Z. H., Mu, W. C. & Huang, S. Y. Design and optimization of a ring-pair permanent magnet array for head imaging in a low-field portable MRI system. IEEE Trans. Magn. 55, 1–8 (2019).

    Google Scholar 

  17. 17.

    Sarty, G. E. & Vidarsson, L. Magnetic resonance imaging with RF encoding on curved natural slices. Magn. Reson. Imaging 46, 47–55 (2018).

    PubMed  Google Scholar 

  18. 18.

    Moore, G. E. Cramming more components onto integrated circuits, reprinted from Electronics, volume 38, number 8, April 19, 1965, pp.114 ff. IEEE Solid-State Circuits Soc. Newsl. 11, 33–35 (2006).

    Google Scholar 

  19. 19.

    Cooley, C. Z. et al. Two-dimensional imaging in a lightweight portable MRI scanner without gradient coils. Magn. Reson. Med. 73, 872–883 (2015).

    PubMed  Google Scholar 

  20. 20.

    Halbach, K. Design of permanent multipole magnets with oriented rare earth cobalt material. Nucl. Instrum. Methods 169, 1–10 (1980).

    CAS  Google Scholar 

  21. 21.

    Stockmann, J. P., Cooley, C. Z., Guerin, B., Rosen, M. S. & Wald, L. L. Transmit array spatial encoding (TRASE) using broadband WURST pulses for RF spatial encoding in inhomogeneous B0 fields. J. Magn. Reson. 268, 36–48 (2016).

    CAS  PubMed  PubMed Central  Google Scholar 

  22. 22.

    Cooley, C. Z., Stockmann, J. P., Sarracanie, M., Rosen, M. S. & Wald, L. L. 3D imaging in a portable MRI scanner using rotating spatial encoding magnetic fields and transmit array spatial encoding (TRASE). Proc. Intl Soc. Mag. Reson. Med. 23, 0703 (2015).

    Google Scholar 

  23. 23.

    McDaniel, P., Cooley, C. Z., Stockmann, J. P. & Wald, L. L. A target-field shimming approach for improving the encoding performance of a lightweight Halbach magnet for portable brain MRI. Proc. Intl Soc. Mag. Reson. Med. 27, 0215 (2019).

    Google Scholar 

  24. 24.

    Casabianca, L. B., Mohr, D., Mandal, S., Song, Y.-Q. & Frydman, L. Chirped CPMG for well-logging NMR applications. J. Magn. Reson. 242, 197–202 (2014).

    CAS  PubMed  Google Scholar 

  25. 25.

    Hennig, J., Nauerth, A. & Friedburg, H. RARE imaging: a fast imaging method for clinical MR. Magn. Reson. Med. 3, 823–833 (1986).

    CAS  PubMed  Google Scholar 

  26. 26.

    Casanova, F., Perlo, J., Blümich, B. & Kremer, K. Multi-echo imaging in highly inhomogeneous magnetic fields. J. Magn. Reson. 166, 76–81 (2004).

    CAS  PubMed  Google Scholar 

  27. 27.

    McDaniel, P. C., Cooley, C. Z., Stockmann, J. P. & Wald, L. L. The MR Cap: a single-sided MRI system designed for potential point-of-care limited field-of-view brain imaging. Magn. Reson. Med. 82, 1946–1960 (2019).

    PubMed  PubMed Central  Google Scholar 

  28. 28.

    Hennig, J. et al. Parallel imaging in non-bijective, curvilinear magnetic field gradients: a concept study. Magn. Reson. Mater. Phys. 21, 5–14 (2008).

    Google Scholar 

  29. 29.

    Stockmann, J. P., Ciris, P. A., Galiana, G., Tam, L. & Constable, R. T. O-space imaging: highly efficient parallel imaging using second-order nonlinear fields as encoding gradients with no phase encoding. Magn. Reson. Med. 64, 447–456 (2010).

    PubMed  PubMed Central  Google Scholar 

  30. 30.

    Fessler, J. A. Model-based image reconstruction for MRI. IEEE Signal Process. Mag. 27, 81–89 (2010).

    PubMed  PubMed Central  Google Scholar 

  31. 31.

    Schultz, G. et al. Reconstruction of MRI data encoded with arbitrarily shaped, curvilinear, nonbijective magnetic fields. Magn. Reson. Med. 64, 1390–1403 (2010).

    PubMed  Google Scholar 

  32. 32.

    Lin, F.-H. et al. Reconstruction of MRI data encoded by multiple nonbijective curvilinear magnetic fields. Magn. Reson. Med. 68, 1145–1156 (2012).

    PubMed  PubMed Central  Google Scholar 

  33. 33.

    Heye, T. et al. The energy consumption of radiology: energy- and cost-saving opportunities for CT and MRI operation. Radiology 295, 593–605 (2020).

    PubMed  Google Scholar 

  34. 34.

    Srinivas, S. A., Cooley, C. Z., Stockmann, J. P., McDaniel, P. C. & Wald, L. L. Retrospective electromagnetic interference mitigation in a portable low field MRI system. Proc. Intl Soc. Mag. Reson. Med. 28, 1269 (2020).

    Google Scholar 

  35. 35.

    Rearick, T., Charvat, G. L., Rosen, M. S. & Rothberg, J. M. Noise suppression methods and apparatus. US patent US9797971B2 (2017).

  36. 36.

    Stockmann, J., McDaniel, P., Vaughn, C., Cooley, C. Z. & Wald, L. L. Feasibility of brain pathology assessment with diffusion imaging on a portable scanner using a fixed encoding field. Proc. Intl Soc. Mag. Reson. Med. 27, 1196 (2019).

    Google Scholar 

  37. 37.

    Cooley, C. Z., McDaniel, P. C., Stockmann, J. P., Mateen, F. J. & Wald, L. L. Single-sided magnet design for an MR guided lumbar puncture (LP) device. Proc. Intl Soc. Mag. Reson. Med. 28, 1266 (2020).

    Google Scholar 

  38. 38.

    McDaniel, P., Cooley, C. Z., Stockmann, J. P. & Wald, L. L. 3D imaging with a portable MRI scanner using an optimized rotating magnet and gradient coil. Proc. Intl Soc. Mag. Reson. Med. 26, 0029 (2018).

    Google Scholar 

  39. 39.

    Bringout, G., Gräfe, K. & Buzug, T. M. Performance of shielded electromagnet—evaluation under low-frequency excitation. IEEE Trans. Magn. 51, 1–4 (2015).

    Google Scholar 

  40. 40.

    Arango, N., Stockmann, J. P., Witzel, T., Wald, L. L. & White, J. Open-source, low-cost, flexible, current feedback-controlled driver circuit for local B0 shim coils and other applications. Proc. Intl Soc. Mag. Reson. Med. 24, 1157 (2016).

    Google Scholar 

  41. 41.

    LaPierre, C., Sarracanie, M., Waddington, D. E. J., Rosen, M. S. & Wald, L. L. A single channel spiral volume coil for in vivo imaging of the whole human brain at 6.5 mT. Proc. Intl Soc. Mag. Reson. Med. 23, 1793 (2015).

    Google Scholar 

  42. 42.

    Anand, S., Stockmann, J. P., Wald, L. L. & Witzel, T. A low-cost (<$500 USD) FPGA-based console capable of real-time control. Proc. Intl Soc. Mag. Reson. Med. 26, 0948 (2018).

    Google Scholar 

  43. 43.

    Blücher, C. et al. COSI transmit: open source soft- and hardware transmission system for traditional and rotating MR. Proc. Intl Soc. Mag. Reson. Med. 25, 0184 (2017).

    Google Scholar 

  44. 44.

    Kunz, D. Frequency-modulated radiofrequency pulses in spin-echo and stimulated-echo experiments. Magn. Reson. Med. 4, 129–136 (1987).

    CAS  PubMed  Google Scholar 

  45. 45.

    Carr, H. Y. & Purcell, E. M. Effects of diffusion on free precession in nuclear magnetic resonance experiments. Phys. Rev. 94, 630–638 (1954).

    CAS  Google Scholar 

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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.

Author information




C.Z.C., P.C.M., J.P.S., S.A.S., C.R.S., C.F.V., M.S., M.S.R. and L.L.W. contributed to or advised on system design, implementation and validation experiments. C.Z.C., J.P.S., S.F.C. and B.G. contributed to development of the image reconstruction method. M.H.L. provided guidance for clinical application and subsequent design choices. C.Z.C. wrote the manuscript. All authors contributed to reviewing and editing the manuscript.

Corresponding author

Correspondence to Clarissa Z. Cooley.

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Competing interests

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).

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