Fluorescence Lymph Node Mapping in Living Mice Using Quantum Dots and a Compression Technique

The lymphatic system is essential in oncology and immunology, and in vivo fluorescence imaging plays a major role in assessing the lymphatic drainage. We investigated non–invasive fluorescence lymph node mapping in mice with special reference to the assessment of deep abdominal lymph nodes. Quantum dots were injected subcutaneously into the rear footpads of mice, and the time course of the fluorescent signal was assessed. Visualization of abdominal lymph nodes was compared with and without compression of the abdomen with transparent, colorless tape at injection doses of 1, 5, and 20 pmol. Popliteal, sacral, iliac, and renal lymph nodes were delineated by non–invasive imaging. Lymph node signals increased up to 3 h after injection. Compression of the abdomen markedly improved the visualization of the iliac nodes, which were invisible at 5 pmol without compression and visible at 1 pmol with compression. Fluorescence lymph node mapping using quantum dots allowed the visualization of deep abdominal lymph nodes in addition to superficial nodes in intact mice, with the aid of a simple compression technique.