MR lymphography: study of a high-efficiency lymphotrophic agent.

PURPOSE: To investigate the utility of a monocrystalline iron oxide nanoparticle (MION) as a contrast agent in magnetic resonance (MR) imaging of lymph nodes. MATERIALS AND METHODS: Pharmacokinetic data were obtained in rats after intravenous, subcutaneous, and intraarterial injection of indium-111-MION-46. MR imaging was performed to determine optimal dosages and pulse sequences in rats. Models of lymph node metastasis in rabbits and lymph node hyperplasia in rats were used to demonstrate the efficacy of MION in differentiation of malignant and benign adenopathies. RESULTS: Biokinetic data indicate that nodal accumulation occurs primarily after extravasation of agent into the interstitial space (slow component) and subsequent trapping by lymph node macrophages (fast component). Relatively low concentrations (15-25 mumol Fe per kilogram for peripheral nodes after intraarterial injection) decrease signal intensity of nodes at MR imaging. CONCLUSIONS: Lymph node accumulation of MION-46 is high. Modification of injection techniques that alter capillary permeability allows use of systemically administered agent at doses as low as 15-25 mumol Fe per kilogram.