A scan of the thyroid gland after injection of radioactive iodine or technetium allows the radioactive density of a thyroid nodule to be differentiated and compared with the density of the surrounding normal thyroid tissue and to draw conclusions. A higher density is called a “hot nodule”; a nodule that is equal to normal tissue is called a “warm nodule”; a nodule that is weaker than normal is called a “cool nodule”; and a nodule that is completely absent is called a “cold nodule”. “Cold nodules”. A single “cold nodule” with blurred margins is more likely to be malignant; “warm nodules” are more likely to be benign adenomas and less likely to be carcinomas; and “hot nodules” are almost always benign. It is important to note that although almost all thyroid cancers are “cold nodules”, “cold nodules” are not always thyroid cancers. Cysts formed in benign nodular goiter due to poor blood circulation, bleeding or degenerative changes can also appear as “cold nodules”, although their edges are usually clearer. If the nodule is solid on ultrasound and “cold nodule” on nuclear scan, the possibility of malignancy is high. Thyroid adenomas may appear as “warm or cool nodules”, and non-functioning adenomas may also be “cold nodules”, which tend to have clear margins, although some may be slightly blurred. In a few cases, it is important to be aware that thyroid cancer (cold nodules) may be misdiagnosed as “cool nodules” due to the overlying normal thyroid tissue. In addition, to further differentiate between benign and malignant nodules, a scanning image (thyroid MIBI nuclide) can be performed using a pro-tumorigenic radioactive element (cesium, selenium, etc.); if there is a concentration of radioactivity in a nodule, it is more likely to be malignant, and conversely, if there is no concentration, it is more likely to be benign.