3D MPI MAA-SPIO scans in vivo rats 10 minutes after IV injection, with coronal, sagittal and axial MIPs shown. (a) 700,000 MAA-SPIOs, with approximately 1.4×105 SPIO particles per MAA cluster (0.4 mg Fe/kg), effectively target to the lung vasculature within 10 minutes by lodging in the lung capillary due to MAA-SPIO particle size larger than capillary diameter. (b) SPIOs (0.4 mg Fe/kg) alone do not target to the lung and instead immediately clear to the liver and spleen in 10 minutes. Streaking artifacts are apparent due to imperfect respiratory gating. Coregistration to CT. Colorbar in µg Fe/cm3.