In vivo 3D brain and extremity MRI at 50 mT using a permanent magnet Halbach array

Thomas O’Reilly, Wouter M. Teeuwisse, Danny de Gans, Kirsten Koolstra, Andrew G. Webb*

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

15 Citations (Scopus)
21 Downloads (Pure)


Purpose: To design a low-cost, portable permanent magnet-based MRI system capable of obtaining in vivo MR images within a reasonable scan time. Methods: A discretized Halbach permanent magnet array with a clear bore diameter of 27 cm was designed for operation at 50 mT. Custom-built gradient coils, RF coil, gradient amplifiers, and RF amplifier were integrated and tested on both phantoms and in vivo. Results: Phantom results showed that the gradient nonlinearity in the y-direction and z-direction was less than 5% over a 15-cm FOV and did not need correcting. For the x-direction, it was significantly greater, but could be partially corrected in postprocessing. Three-dimensional in vivo scans of the brain of a healthy volunteer using a turbo spin-echo sequence were acquired at a spatial resolution of 4 × 4 × 4 mm in a time of about 2 minutes. The T1-weighted and T2-weighted scans showed a good degree of tissue contrast. In addition, in vivo scans of the knee of a healthy volunteer were acquired at a spatial resolution of about 3 × 2 × 2 mm within 12 minutes to show the applicability of the system to extremity imaging. Conclusion: This work has shown that it is possible to construct a low-field MRI unit with hardware components costing less than 10 000 Euros, which is able to acquire human images in vivo within a reasonable data-acquisition time. The system has a high degree of portability with magnet weight of approximately 75 kg, gradient and RF amplifiers each 15 kg, gradient coils 10 kg, and spectrometer 5 kg.

Original languageEnglish
Pages (from-to)495-505
Number of pages11
JournalMagnetic Resonance in Medicine
Issue number1
Publication statusPublished - 2021


  • gradient design
  • Halbach array
  • low-field MRI
  • permanent magnets
  • sustainable imaging


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