In vivo identification of sentinel lymph nodes using MRI and size-controlled and monodispersed magnetite nanoparticles

Purpose: To develop a sentinel lymph node (SN) identification method using accurately synthesized magnetic nanoparticles (MNPs), as an enhanced specific SN tracer in combination with magnetic resonance imaging (MRI) in intact rodent and SN metastasis models. Materials and Methods: Three sizes of MNPs were originally synthesized. We developed an experimental rat SN model, with brachial lymph nodes (Br) as the SN and the axillary lymph node (Ax) as the second lymph node, and injection of MNPs via the front paw. SN detectability was evaluated in vivo using T₁-weighted MR images after injection of the synthesized MNPs, and the amount of iron in the Br and in the Ax was assessed using inductively coupled plasma optical emission spectrometry. Results: The highest ratios of the amount of iron in the Br versus the Ax were 3.1 and 3.3, using 20-nm MNPs after 2- and 24-hour injections. The appropriate dose and particle diameter for MRI detection was optimized, and the SN was optimally distinguished in the normal and metastatic rat models using MRI after a 0.4 mg/kg 20-nm MNP injection. Conclusion: We developed and optimized a useful SN identification method using MRI in rodent models.