Quantitative Evaluation of the Reticuloendothelial System Function with Dynamic MRI

PURPOSE: To evaluate the reticuloendothelial system (RES) function by real-time imaging blood clearance as well as hepatic uptake of superparamagnetic iron oxide nanoparticle (SPIO) using dynamic magnetic resonance imaging (MRI) with two-compartment pharmacokinetic modeling. MATERIALS AND METHODS: Kinetics of blood clearance and hepatic accumulation were recorded in young adult male 01b74 athymic nude mice by dynamic T2* weighted MRI after the injection of different doses of SPIO nanoparticles (0.5, 3 or 10 mg Fe/kg). Association parameter, K(in), dissociation parameter, K(out), and elimination constant, K(e), derived from dynamic data with two-compartment model, were used to describe active binding to Kupffer cells and extrahepatic clearance. The clodrosome and liposome were utilized to deplete macrophages and block the RES function to evaluate the capability of the kinetic parameters for investigation of macrophage function and density. RESULTS: The two-compartment model provided a good description for all data and showed a low sum squared residual for all mice (0.27±0.03). A lower K(in), a lower K(out) and a lower K(e) were found after clodrosome treatment, whereas a lower K(in), a higher K(out) and a lower K(e) were observed after liposome treatment in comparison to saline treatment (P<0.005). CONCLUSION: Dynamic SPIO-enhanced MR imaging with two-compartment modeling can provide information on RES function on both a cell number and receptor function level.