%0 Journal Article %J Journal of Low Temperature Physics %D 2004 %T SQUID-detected magnetic resonance imaging in microtesla magnetic fields %A McDermott, R. %A Kelso, N. %A Lee, S. K. %A Mossle, M. %A Mück, M. %A Myers, W. %A ten Haken, B. %A Seton, H. C. %A Trabesinger, A. H. %A Pines, A. %A Clarke, J. %K mri %X

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.

%B Journal of Low Temperature Physics %V 135 %P 793-821 %8 Jun %@ 0022-2291 %G English %U ://WOS:000221710600023 %N 5-6 %M WOS:000221710600023 %! SQUID-detected magnetic resonance imaging in microtesla magnetic fields %R Doi 10.1023/B:Jolt.0000029519.09286.C5