Fig. 1

a Staining of lymph nodes by carbon nanoparticles. The specimen of central neck dissection shows that the lymph nodes at the drainage area of the thyroid lymph were stained black by the carbon nanoparticles. The circles indicate CNs stained lymph nodes. b The thyroid gland was stained black by carbon nanoparticles, while the parathyroid gland was not. Carbon nanoparticle suspension was injected into normal thyroid tissue at two or three spots randomized and uniformed distributed at the upper, median, and lower part of thyroid lobe. Then, thyroid tissue was stained black but the parathyroid glands were not because of sharing different lymphatic system from thyroid. →indicates black stained thyroid tissue, ←indicates parathyroid gland