A practical and flexible implementation of 3D MRI in the Earth's magnetic field

Meghan E. Halse, Andrew Coy, Robin Dykstra, Craig Eccles, Mark Hunter, Rob Ward, Paul T. Callaghan

Research output: Contribution to journalArticlepeer-review


The Earth's magnetic field, though weak, is appealing for NMR applications because it is highly homogeneous, globally available and free. However, the practicality of Earth's field NMR (EFNMR) has long been limited by the need to perform experiments in outdoor locations where the local field homogeneity is not disrupted by ferrous or magnetic objects and where ultra-low frequency (ULF) noise sources are at a minimum. Herein we present a flexible and practical implementation of MRI in the Earth's magnetic field that demonstrates that EFNMR is not as difficult as it was previously thought to be. In this implementation, pre-polarization and ULF noise shielding, achieved using a crude electromagnet, are used to significantly improve signal-to-noise ratio (SNR) even in relatively noisy environments. A three axis gradient coil set, in addition to providing imaging gradients, is used to provide first-order shims such that sub-hertz linewidths can routinely be achieved, even in locations of significant local field inhomogeneity such as indoor scientific laboratories. Temporal fluctuations in the magnitude of the Earth's magnetic field are measured and a regime found within which these variations in Larmor frequency produce no observable artefacts in reconstructed images.
Original languageEnglish
Pages (from-to)75-83
Number of pages9
JournalJournal of Magnetic Resonance
Issue number1
Early online date7 Jul 2006
Publication statusPublished - Sept 2006


  • MRI
  • Imaging
  • Earth's magnetic field

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