Characterization of magnetic nanoparticles as contrast agents in magnetic resonance imaging using high-T_c superconducting quantum interference devices in microtesla magnetic fields

In this paper, we characterize the spin-lattice relaxation T₁, spin-spin relaxation T₂, and effective relaxation rate Γ_MF of magnetic fluids for magnetic resonance imaging using a high-T_c superconducting quantum interference device (SQUID) in microtesla magnetic fields. When the magnetic susceptibility of the magnetic fluid was increased, a broadening of proton nuclear magnetic resonance spectra and a growing spin-lattice relaxation T₁ as well as spin-spin relaxation T₂ were observed. The effective relaxation rate Γ_MF increased monotonically from 0 to 13 s^-1 when the magnetic susceptibility of the magnetic fluids, relative to tap water, was increased from 0 to 0.0015 emu g^-1. We demonstrate the magnetic fluid as an image contrast via a high-T_c SQUID in microtesla magnetic fields.