Investigations of the T1 Temperature Dependence of Protons in Water and Contrast Agents Using a High-Tc DC-SQUID-Based ULF NMR System

The temperature dependence of proton's spin-lattice relaxation time T1 in water samples and Gd-based contrast agents with a measurement field of 72 μT was systematically studied by dc-SQUID-based ultralow field (ULF) nuclear magnetic resonance (NMR) spectrometer. The temperature of samples was controlled by a thermostatic bath and the standard error of T1 was around 0.01 s within five different groups, the results showed that T1 had a similar linear temperature dependence when it was compared to conventional NMR data and varied with the purity of the water samples. Then, the relaxivity r1 of Gd-based metal-organic frameworks (MOFs) and Gd-DTPA (where DTPA is diethylene triamine pentaacetate) were also studied. Both of them had a much higher r1 in ULF NMR than conventional NMR, which was around 45 mM
^-1
·s
^-1
and 98 mM
^-1
·s
^-1
, respectively; however, the T1 of Gd-based contrast agents did not follow the linear temperature dependence, and the relaxivity r1 would not be influenced by temperature, which implies Gd-MOFs and Gd-DTPA are also high performance T 1 contrast agents in ULF NMR and MRI.