All MR images were acquired on a 9.4 T 31 cm MRI scanner (Agilent Technologies) with software designed for pre-clinical MR imaging research (Vnmrj, Agilent Technologies). A custom three-loop volume coil was used. Both 3D multi-band SWIFT (MB-SWIFT) and 3D gradient echo (GRE) images were acquired (25 (link)). MR imaging was performed at 4 h and 24 h after loading and then unloading msIONPs from the lumen of an artery. The detailed methods are given in the Supplementary Materials and closely follow previous protocols (25 (link)).