The thyroid gland is the largest endocrine gland in the body. This gland is divided into two lobes, located on either side of the trachea and connected in the middle (called the isthmus), and is “H” shaped, with about 20-30 grams. It can move up and down with the larynx when swallowing. The main function of the thyroid gland is to produce thyroid hormones (including TT3, TT4, FT3, FT4). Thyroid hormones play an important role in human growth and development and regulation of organ functions. The thyroid gland has a strong aggregation effect on iodine, and 90% of the whole body iodine content is concentrated in the thyroid gland.