Characterization of ultrasmall, paramagnetic magnetite particles as superparamagnetic contrast agents in MRI

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 R1 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.s; and R2, 19 L/mmol.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.