Ultralow-Field High-Tc SQUID NMR/MRI System With a 77-K Cooled Copper Flux Transformer

We propose a high-T
_c
superconducting quantum interference device ultralow-field magnetic resonance imaging (ULF MRI) system for food inspection. Although the ULF MRI is compact and low cost, compared with a conventional high-field MRI, the detected signal is extremely weak. Thus, a nuclear magnetic resonance (NMR) system was constructed and optimized before realizing the MRI system. The purpose of the study is to improve the signal-to-noise ratio (SNR) of the NMR signal. A copper-wound flux transformer cooled at 77 K by liquid nitrogen and
$\mbox{LC}$
resonance were employed and tested to improve the SNR. As a result, the measured SNR was approximately equal to 236 with
$\mbox{LC}$
resonance, improving by a factor of 7.8.