Characterization of ultrasmall magnetite [correction of paramagnetic magnetite] particles as superparamagnetic contrast agents in MRI.

Overview

RATIONALE AND OBJECTIVES: Very small dextran-coated magnetite particles were developed. These particles can be used either as immunospecific contrast agents for MRI by coupling to antibodies or as an interstitial contrast agent. METHODS: The particles were synthesized from iron chloride/dextran solutions. Size was evaluated by electron microscopy and photon correlation spectroscopy. The iron concentration was determined by x-ray spectroscopy. T1 and T2 values as well as relaxivities RI and R2 were evaluated with a clinical MR scanner at 1.5 T. Biocompatibility assays were performed with the cell line U937 in methylcellulose cultures. RESULTS: Superparamagnetic, dextran-coated magnetite particles with a hydrodynamic diameter of 10 nm were developed. The iron core size was 7 nm; R1,7 L/mmol x s; and R2, 19 L/mmol x s. These particles are smaller than those currently available commercially and therefore show a smaller R1 to R2 ratio. Biocompatibility tests have shown no toxic side effects so far. CONCLUSIONS: Ultrasmall magnetite particles with a dextran coating were developed; the physical properties of these particles evaluated in vitro are described in this study.