A nodule with blood flow signal is an ultrasound description of the richness of blood flow in a nodule. Generally, ultrasound can be divided into 4 levels according to the richness of blood flow, with level 0 indicating no obvious blood flow signal and level 3 indicating a rich blood flow signal. Normally, blood flow signal is an important means to identify a nodule as benign or malignant. The blood supply of malignant masses is richer, suggesting a grade 2-3 blood flow signal, while the blood flow signal of benign nodules is low, mostly a grade 0-1 blood flow signal, so attention should be paid to nodules with rich blood flow signal. However, for some large benign tumors, they may also suggest abundant blood flow signal, while some small malignant nodules may not suggest obvious blood flow signal. Therefore, blood flow signal should not be taken as the only criterion for judgment, and the morphology, boundary, whether the mass grows upright or not, and whether there is calcification, should be combined to judge the nature of the nodule.