A compact SQUID-detected magnetic resonance imaging system under microtesla field in a magnetically unshielded environment

In this study, we present a compact and sensitive SQUID-detected nuclear magnetic resonance spectrometer and imager (NMR/MRI) using flux coupling in microtesla fields. The pre-polarization coil, measuring coil, pulsed coil, and gradient coils were set up inside a three-layer aluminum box while the SQUID-detector was shielded with a high-T_c superconducting vessel. A compensation field was applied to improve the field homogeneity in magnetically unshielded environments. The spin precession of protons was inductively coupled to the SQUID magnetometer via a resonant flux transformer. We obtained a signal-to-noise ratio of 120 in one measurement, a spectral resolution better than 1 Hz, and a spatial resolution of 1.3 mm in the images.