Size and Compositional Effects on Contrast Efficiency of Functionalized Superparamagnetic Nanoparticles at Ultralow and Ultrahigh Magnetic Fields

Magnetic resonance imaging (MRI) systems at ultralow and ultrahigh field have been developed for biomedical imaging. We synthesized and functionalized superparamagnetic (SPM) nanoparticles (NPs) and studied the spin–lattice (<i>T</i>₁) and spin–spin (<i>T</i>₂) relaxation time of protons in water surrounding these NPs at ultralow and at ultrahigh magnetic fields. In these fields, size and compositional effects of SPM NPs were observed contributing to the spin–lattice (<i>r</i>₁) and spin–spin (<i>r</i>₂) relaxivities as well as <i>r</i>₂/<i>r</i>₁ ratios. These results reveal the relationship between magnetic characteristics of SPM NPs and relaxation behavior of water proton at ultralow or ultrahigh field