Microtesla NMR and High Resolution MR Imaging Using High- $T_{\rm c}$ SQUIDs

In this work, we set up a low-cost high-
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SQUID-based low-field nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) system without μ-metal. In order to reduce the surrounding noise, we built the shielded box and shielded cylinder made out of aluminum. For NMR and MRI measurements, we apply the gradient compensation field to cancel the field inhomogeneity in our lab to obtain a narrow linewidth NMR spectrum of 0.8 Hz from a 10-ml water specimen. In the absence of chemical shifts, the J-couplings of trimethyl phosphate and trifluoroethanol are demonstrated in trials of the proposed scheme. Furthermore, the 2-D images of water specimen and mini tomato with high-image resolution of better than 2 mm are obtained by using our low-field MRI system. Our high-
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SQUID-based low-field MRI system promises a low-cost and high imaging quality in microtesla magnetic fields.