The blood flow signal seen in the nodule is an expression of the abundance of blood flow in the nodule according to the color ultrasound. The degree of blood flow can generally be divided into four grades from 0 to 3. If the ultrasound indicates grade 0, it means that no obvious blood flow signal is seen, and if the ultrasound indicates grade 3, it means that there is abundant blood flow signal. In general the blood flow signal is the main means of identifying whether the nodule is benign or malignant. Because the malignant mass has a high blood supply, it will suggest a grade 2-3 blood flow signal, while a benign nodule with a very low blood flow signal will suggest a grade 0-1 blood flow signal. However, the blood flow signal should not be taken as the only criterion for determining the benign or malignant nature of the nodule. For some very large benign nodules, the blood flow signal may also indicate grade 2-3, and on the contrary, for some relatively small malignant nodules, the blood flow signal may also indicate grade 0-1, therefore, it is necessary to go to the hospital in time to do a comprehensive examination to comprehensively determine the nature of the nodule.