A dendrimer-based nanosized contrast agent dual-labeled for magnetic resonance and optical fluorescence imaging to localize the sentinel lymph node in mice

Purpose To preoperatively and intraoperatively localize the sentinel lymph node (SLN), a single hybrid probe for MR and near infrared (NIR) optical imaging was synthesized and tested. Materials and Methods A macromolecular MR/NIR optical contrast agent was synthesized based on a ∼191 gadolinium‐labeled contrast agent using generation‐6 polyamidoamine dendrimer (G6), which is also labeled with 2 Cy5.5, an NIR fluorophore. After establishing the optimal dose, the agent was injected into mammary glands of 10 normal mice to examine the lymphatic drainage from the breast using a 3T clinical scanner. Immediately after the MRI scan, NIR optical imaging and image‐guided surgery were performed to compare the two imaging modalities. Results To consistently identify the SLNs, we needed to inject 25 μL of 30 mM [Gd] G6‐Cy5.5. All SLNs could be easily identified and resected under NIR optical imaging‐guided surgery. Although external NIR optical imaging failed to identify SLNs close to the injection site due to shinethrough, MR lymphography (MRL) consistently identified all SLNs regardless of their location. Conclusion We have successfully synthesized and tested a dual labeled MR/NIR optical hybrid contrast agent, G6‐Cy5.5 for reoperative and intraoperative localization of SLNs. J. Magn. Reson. Imaging 2007. © 2007 Wiley‐Liss, Inc.