Detection and quantitation in rat tissues of the superparamagnetic magnetic resonance contrast agent dextran magnetite as demonstrated by electron spin resonance spectroscopy.

RATIONALE AND OBJECTIVES: The compound studies in this article is a superparamagnetic macromolecular complex of magnetite cores coated with hydrophilic dextran, which is under active investigation as a contrast agent for magnetic resonance imaging (MRI) in liver and spleen. The biodistribution of paramagnetic compounds is problematic and is usually studied by histochemical reactions or by radiolabeling the compound under study. The purpose of this article is to show how electron spin resonance (ESR) spectroscopy detects dextran magnetite (DM) particles in tissues. METHODS: DM injected intravenously in the experimental animal was detected in some reticulo-endothelial organs by ESR. The spectroscopic study was validated using electron microscopy and electron-probe microanalysis. RESULTS: DM exhibits an ESR spectrum; ESR delineated the distribution of DM distribution in liver, spleen, bone marrow, and blood as a function of time. The blood clearance was biphasic, dependent on the size of particles. CONCLUSIONS: ESR spectroscopy is a highly sensitive and reproducible method of studying DM distribution.