Relaxation rates of protons in gadolinium chelates detected with a high-T_c superconducting quantum interference device in microtesla magnetic fields

A nuclear magnetic resonance and imaging system was constructed to study spin-lattice relaxation time T₁, spin-spin relaxation time T ₂, and effective relaxation time T2 of gadolinium (Gd) chelates using a high- Tc superconducting quantum interference device in microtesla magnetic fields. In the presence of the magnetic contrast T2 is related to T₂ by the relation: 1/ T2 =1/ T₂ +γΔB+ Gd-chelates, where γ=42.58 kHz/mT and γΔB is the relaxation rate due to the inhomogeneity field ΔB in measuring coil at the sample position and Gd-chelates is the intrinsic relaxation rate of Gd chelates. It is found that T₁, T₂, and 1/ Gd-chelates decay exponentially as the concentration (or magnetic susceptibility) of Gd chelates increases. The Gd chelates cause a diffusive motion of nuclear spins and hence enhance the relaxation rates. Enhanced image contrast has been demonstrated in a water phantom with Gd chelates in microtesla magnetic fields.