fig2

Figure 2. A: Following intravenous injection, SPIONs slowly extravasate from vascular space to interstitial space, from where they can be taken up by immune cells (monocytes/macrophages) and delivered via lymphatic vessels to lymph nodes. The SPIONs remain in normal nodal tissue and reduce MRI signal intensity, thereby enhancing contrast against any metastatic lesions in the node; B and C: demonstrating the mechanism of negative contrast agent, SPIONs in lymph node imaging; B: a conventional T2-weighted MR image of the lymph node showing the whole lymph node is associated with cancer metastases; C: the T2-weighted MR image of the lymph node with enhanced contrast produced by SPIONs showing only two small metastatic regions (e.g., hyper intense foci). The MR images in B and C were reproduced^[96]. SPION: superparamagnetic iron oxide nanoparticle; MRI: magnetic resonance imaging