In this paper, we characterize the spin-lattice relaxation T1, spin-spin relaxation T2, and effective relaxation rate ΓMF of magnetic fluids for magnetic resonance imaging using a high-Tc 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 ΓMF 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-Tc SQUID in microtesla magnetic fields.
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