USPIO (Ferumoxtran-10)-enhanced MRI to visualize reticuloendothelial system cells in neonatal rats: feasibility and biodistribution study.

Purpose: To investigate whether USPIO-enhanced magnetic resonance imaging (MRI) detected reticuloendothelial system (RES) cells in newborn normal rats.

Materials And Methods: Newborn normal rats were imaged in vivo on a 1.5 T MR system, 2-96 hours after intraperitoneal Ferumoxtran-10 (n = 38) or saline injection (control group, n = 5). Signals from liver, spleen, and vertebral bone marrow were measured (T2-weighted Turbo Spin Echo) to describe the kinetics of enhancement. The pups were sacrificed and iron concentrations in plasma and peritoneal fluid were measured using atomic absorption spectrometry. Prussian blue-labeled cells density in liver, spleen, and vertebral bone marrow was assessed.

Results: Significant (P < 0.05) negative enhancement of the liver, spleen, and vertebral bone marrow was noted after Ferumoxtran-10 injection (2-96 hours for liver and spleen, 4-96 hours for bone marrow). Ferumoxtran-10 was absorbed from the peritoneum in the first 8 hours postinjection, entering the circulation with a plasma peak (8 hours); then Ferumoxtran-10 returned over the baseline in plasma (96 hours). Important intracellular iron deposition in liver and spleen was measured postinjection (3-96 hours, P < 0.05). Limited but significant intracellular iron deposition was noted in vertebral bone marrow postinjection (96 hours, P < 0.05), suggesting that Ferumoxtran-10 selectively labeled RES cells after 96 hours and produced nonspecific labeling at earlier timepoints.

Conclusion: Ferumoxtran-10-enhanced MRI visualizes RES cells in vivo in newborn rats.