Retention of cells in the IB space by PET/CT imaging following OIB injection with⁸⁹Zr-oxine–labeled CD34⁺cells. Right posterior superior iliac spine of a 10 kg of RM was injected using the OIB method with 48.1 kBq (1.3 µCi)/2.9 × 10⁶ (0.29 × 10⁶/kg) labeled autologous CD34⁺ HSPCs. PET/CT imaging and quantification of isotope uptake from cells at the injection site and whole body was then performed. (A) Images at 10 minutes after OIB injection. (B) Regions of interest (ROIs) as a tool to calculate uptake at different anatomical sites as a percentage of injected dose: 1 hour after injection, 78% of injected cells were retained at the injection site with ∼15% distributed to liver/spleen/other marrow sites. The remaining 7% activity was detected mainly in the kidneys and bladder, consistent with deferoxamine chelation and urinary excretion of free ⁸⁹Zr released from dead or dying cells.