To understand the size, shape, location, and functional status of the thyroid gland and to estimate the weight of the thyroid gland. Diagnosis of ectopic thyroid: If metastatic thyroid cancer is excluded, ectopic thyroid can be diagnosed when 131 iodine images are not seen in the normal thyroid area but appear in other areas. The ectopic thyroid gland is usually the result of abnormal embryonic development and is usually located at the root of the tongue, under the hyoid bone and behind the sternum. Differential diagnosis of thyroid nodules: Based on the level of reactivity of the thyroid nodule site, nodules are classified into four types, namely hot nodules, warm nodules, cool nodules, and cold nodules, the results of which are clinically important for the differentiation of benign and malignant nodules. According to the statistics, there are few warm nodules and hot nodules are malignant, while the malignancy rate of cold nodules is higher, especially single cold nodules should be highly alert to whether they are malignant. Diagnosis of carcinoma in situ of the thyroid gland: cold nodules can be re-imaged with a “pro-tumor” imaging agent, and if there is radioactive concentration in the original cold nodule site, it indicates a higher possibility of malignancy, while if there is no radioactive concentration, it is more likely to be benign. Diagnosis of subacute thyroiditis (subacute thyroiditis): In patients with untreated subacute thyroiditis, the thyroid image is unclear or irregular, and in the middle and late stages, the thyroid gland is often unrevealing or sparse, and the outline of the thyroid gland is unclear. To determine the relationship between the neck mass and the thyroid gland: if the thyroid image contour is intact and the mass is outside the thyroid image and has no radiological distribution, the mass is generally considered to be unrelated to the thyroid gland. If the mass is located within the thyroid gland contour and the thyroid morphology is incomplete, it is suggested to be an intrathyroidal mass.