For in vivo PET imaging, 150 μL (∼400 μCi or 14.8 MBq) of 89Zr-MSN (or 89Zr-dSiO2) in water was i.v. injected into healthy BALB/c mice (n = 3). PET scans at various time points p.i., from 0.5 h to 21 days, were performed by using a microPET/microCT Inveon rodent model scanner (Siemens Medical Solutions USA, Inc.). The images were reconstructed using a maximum a posteriori algorithm, with no scatter correction. ROI analysis of each PET scan was performed using vendor software (Inveon Research Workplace [IRW]) on decay-corrected whole-body images, as we described previously,40 (link) to calculate the percentage injected dose per gram of tissue (%ID/g) values in mouse liver and bone.