Use of magnetite particles as a contrast agent for MR imaging of the liver.

To evaluate the potential of dextran-coated magnetite (DM) particles in enhancing the detection of hepatocellular carcinoma with magnetic resonance (MR) imaging, the authors induced liver tumors in rats by oral administration of diethylnitrosamine and examined the rats before and after intravenous injections of DM with various iron concentrations. Because of the intense and preferential T2 relaxativity of DM, use of DM with an iron concentration of 10 mumol/kg yielded effective MR signal reduction in each normal liver at 1 hour after the injection. Because no significant signal change in the tumors was observed on DM-enhanced MR images, the contrast between hepatocellular carcinoma and adjacent uninvolved liver increased remarkably on even relatively T1-weighted images. The detection rate for the 89 tumors, including small tumors less than 2 mm in diameter, increased from 10% (nine of 89) before DM administration to 65% (58 of 89) with DM-enhanced T1-weighted imaging. Iron staining of rat liver performed about 1 hour after DM administration showed sparse deposits of DM selectively in reticuloendothelial cells but not in liver tumors.