Abstract
In our study, we constructed a ultra-low field (ULF) nuclear magnetic resonance (NMR)/magnetic resonance imaging (MRI) system employing a high-temperature superconductor (HTS)-rf-SQUID and room-temperature coils. In the system, we employed a pulsed polarizing field Bp perpendicular to a measurement field Bm; a high-speed switching circuit with an optical FET was used to switch off Bp of approximately 30 mT. When a field gradient dBz/dz of approximately 10 nT/cm was applied to a sample, which was designed to contain water in two compartments, a 1H-NMR spectrum with two peaks was observed. The frequency difference between the two peaks roughly corresponded to the distance between each center of the water in the two parts. We measured the 1H -NMR signals for water and mineral oil and found a clear difference in their signal amplitudes owing to their different molecular compositions. The longitudinal relaxation times T1 of water and the oil were also estimated by changing the polarizing time of Bp. From these results, it was confirmed that 1H- and T1-weighted contrast imaging could be realized by using this system.
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