Real-time mapping of rat stomach lymph nodes by quantum dots

To develop a real-time imaging method to identify the rat stomach lymph node basin with quantum dots (Qdots).

Six Sprague-Dawley rats received injections of 0.05 ml Qdots (1 mg/ml) in the subserosal layer in the lesser curvature of the gastric antrum. Subsequently, draining lymphatic channels and lymph nodes were visualized with a near-infrared fluorescence imaging system. Histological examination was required to confirm the presence of lymph nodes. Additionally, rats received injections of Qdots and underwent 2 weeks of observation to confirm if there was any abnormality. The distribution of Qdots was measured by inductively coupled plasma-mass spectrometry.

After injection of the Qdots, the gastric sentinel lymph nodes were visualized 15 min later. The fluorescence then began to spread. The intensity of fluorescence increased in the perigastric area at 60 min, and declined at 360 min. Histological analysis of the fluorescent tissue confirmed the presence of nodal tissue. The results of a cadmium assay showed that Qdots were mainly distributed in the liver, spleen and kidney of the rats. No apparent toxicity could be seen during the 2 weeks of observation.

NIR fluorescence imaging of lymph nodes with Qdots is a novel and reliable real-time technique that can be used to assist with identification and resection of stomach lymph nodes. The optimal observation time of perigastric SLNs was 15 min after the injection, and the optimal observation time of perigastric lymph nodes beyond the SLNs was 60-120 min after the injection.