MR LYMPHOGRAPHY - STUDY OF A HIGH-EFFICIENCY LYMPHOTROPHIC AGENT

PURPOSE: To investigate the utility of a monocrystalline iron oxide na noparticle (MION) as a contrast agent in magnetic resonance (MR) imagi ng of lymph nodes. MATERIALS AND METHODS: Pharmacokinetic data were ob tained in rats after intravenous, subcutaneous, and intraarterial inje ction of indium-111-MION-46. MR imaging was performed to determine opt imal dosages and pulse sequences in rats. Models of lymph node metasta sis in rabbits and lymph node hyperplasia in rats were used to demonst rate the efficacy of MION in differentiation of malignant and benign a denopathies. RESULTS: Biokinetic data indicate that nodal accumulation occurs primarily after extravasation of agent into the interstitial s pace (slow component) and subsequent trapping by lymph node macrophage s (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 accum ulation of MION-46 is high. Modification of injection techniques that alter capillary permeability allows use of systemically administered a gent at doses as low as 15-25 mumol Fe per kilogram.