A novel PAMAM dendrimer-based nanoprobe for dual magnetic resonance and fluorescence imaging modalities was synthesized. Fluorescence studies revealed that Gd(III) complexation to the probe has no effect on the quantum yield; however, increases in the dye content resulted in partial quenching. The potential of the new nanoprobe, G6-(Cy5.5)(1.25)(1B4M-Gd)(145), as a dual modality imaging agent was demonstrated in vivo by the efficient visualization of sentinel lymph nodes in mice by both MRI and fluorescence imaging modalities.

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 ϳ191 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 L of 30 mM [Gd] G6-Cy5.5. All SLNs could be easily identified and resected under NIR optical imagingguided 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.