Dose and scanning delay using USPIO for central nervous system macrophage imaging

Rationale and objectives: In experimental allergic encephalomyelitis (EAE), central nervous system (CNS) macrophage imaging is achievable by MRI using AMI-227 an ultra-small particle iron oxide contrast agent at a dose of 300 μmol/kg Fe. The objective was to test the feasibility at the human recommended dose of 45 μmol/kg Fe.Methods: Two groups of EAE rats were tested with AMI-227 using 45 and 300 μmol/kg Fe respectively. Following i.v. injection of AMI-227, they were scanned after a delay of 4–6 and 20–24 h.Results: With a high dose of AMI-227, all animals showed low signal intensity related to iron-loaded macrophages in the CNS. At low dose no abnormalities were found in the CNS. Furthermore, a delay of 4–6 h failed to demonstrate abnormalities even at high dose.Conclusions: Dose, scanning delay after administration and blood half-life are major parameters for T2^* CNS macrophage imaging.