SQUID-Detected Magnetic Resonance Imaging in Microtesla Magnetic Fields

R. McDermott, N. Kelso, S. K. Lee, M. Moble, M. Muck, W. Myers, B. ten Haken, Hugh Seton, A. H. Trabesinger, A. Pines, J. Clarke

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Abstract

We describe studies of nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance imaging (MRI) of liquid samples at room temperature in microtesla magnetic fields. The nuclear spins are prepolarized in a strong transient field. The magnetic signals generated by the precessing spins, which range in frequency from tens of Hz to several kHz, are detected by a low-transition temperature dc SQUID (Superconducting QUantum Interference Device) coupled to an untuned, superconducting flux transformer configured as an axial gradiometer. The combination of prepolarization and frequency-independent detector sensitivity results in a high signal-to-noise ratio and high spectral resolution (similar to 1 Hz) even in grossly inhomogeneous magnetic fields. In the NMR experiments, the high spectral resolution enables us to detect the 10-Hz splitting of the spectrum of protons due to their scalar coupling to a P-31 nucleus. Furthermore, the broadband detection scheme combined with a non-resonant field-reversal spin echo allows the simultaneous observation of signals from protons and P-31 nuclei, even though their NMR resonance frequencies differ by a factor of 2.5. We extend our methodology to MRI in microtesla fields, where the high spectral resolution translates into high spatial resolution. We demonstrate two-dimensional images of a mineral oil phantom and slices of peppers, with a spatial resolution of about 1 mm. We also image an intact pepper using slice selection, again with 1-mm, resolution. A further experiments we demonstrate T-1-contrast imaging of a water phantom, some parts of which were doped with a paramagnetic salt to reduce the longitudinal relaxation time T-1. Possible applications of this MRI technique include screening for tumors and integration with existing multichannel SQUID systems for brain imaging.

Original languageEnglish
Pages (from-to)793-821
Number of pages28
JournalJournal of Low Temperature Physics
Volume135
Issue number5-6
DOIs
Publication statusPublished - Jun 2004

Keywords

  • SQUID
  • nuclear magnetic resonance
  • magnetic resonance imaging
  • DC SQUID
  • JUNCTIONS
  • NMR
  • NOISE
  • COIL
  • MRI

Cite this

McDermott, R., Kelso, N., Lee, S. K., Moble, M., Muck, M., Myers, W., ten Haken, B., Seton, H., Trabesinger, A. H., Pines, A., & Clarke, J. (2004). SQUID-Detected Magnetic Resonance Imaging in Microtesla Magnetic Fields. Journal of Low Temperature Physics, 135(5-6), 793-821. https://doi.org/10.1023/B:JOLT.0000029519.09286.c5