SUPERPARAMAGNETIC IRON-OXIDE FOR LIVER IMAGING - COMPARISON AMONG 3 DIFFERENT PREPARATIONS

OBJECTIVES. The effects of differently sized superparamagnetic iron oxide (SPIO) particles as liver contrast agents were evaluated by relaxation analysis and magnetic resonance imaging in normal rabbits. METHODS. We performed relaxivity measurements in agarose gels; T1 was measured by saturation recovery. Rabbits were injected with SPIO particles to evaluate hepatocellular localization and magnetic resonance appearance. RESULTS. Small (30 nm), medium (300 nm) and large SPIO particles (3,500 nm) reduced the T2 of liver by 50%, 40% and 15%, respectively, and the T2 of spleen by approximately 60%, 65%, and 25%, respectively, at 1 mg Fe/kg intravenous injection. Both small and medium SPIO particles decreased the T1 of spleen by approximately 35%, with no effect on liver T1. Magnetic resonance imaging showed decreased signal intensity ratios (SIliver/SImuscle) by approximately 80% and 60% for small and medium SPIO particles, respectively. Iron oxide (positive Perls blue staining) was observed in Kupffer cells after injection of medium and large SPIO particles, and also in hepatocytes after injection of small SPIO particles. CONCLUSION. The liver contrast effect seemed to be related to cellular distribution; the widely distributed small SPIO particles were most effective.