Impact of metallic trace elements on relaxivities of iron-oxide contrast agents.

In this work, well-defined 3 nm-sized Ca 2+ , Fe 3+ , Na + , Mg 2+ , Zn 2+ , Ni 2+ , Co 2+ , and Cd 2+ cation-adsorbed Fe 3 O 4 /γ-Fe 2 O 3 nanoparticles were used as prototype systems to investigate the influence of metallic trace elements in body fluids on the relaxivities of iron-oxide contrast agents. It was found that surface-adsorbed cations formed a deterioration layer to induce pronounced relaxivity loss. Theoretical study showed that such relaxivity loss can be well described by a modified GCAS function, taking into account the harmonic cation oscillations around Fe 3 O 4 /γ-Fe 2 O 3 nanoparticles. Quantum mechanics analyses revealed that even-parity and odd-parity states of harmonic oscillations are dominant in r 1 and r 2 relaxivities, respectively. Moreover, the harmonic oscillations of Na + and Mg 2+ cations around Fe 3 O 4 /γ-Fe 2 O 3 nanoparticles are found to be classical forbidden, which are quite different from their counterparts located in the classical permissive area.