Microtesla NMR Measurement of Protons and Fluorine Nuclei Using a SQUID Gradiometer

We have developed a microtesla nuclear magnetic resonance (NMR) system with a low- Tc superconducting quantum interference device gradiometer. We used it to simultaneously measure the free induction decay (FID) signals of water (15 ml) and perfluorooctane (15 ml). The static field and prepolarization field were 50 μT and 17 mT, respectively. The gradiometer was an axial-second-order type with a diameter of 50 mm and a baseline of 70 mm. NMR spectra were obtained by fast Fourier transformation of the FID signal. Two peaks, one for protons and one for fluorine nuclei, were clearly obtained without averaging. These results demonstrate that the developed microtesla NMR system can simultaneously detect NMR signals originating from multiple nuclei.