Blood flow signals can indicate the blood flow supply in and around a tissue, organ or tumor, and the amount of blood flow signals does not necessarily indicate the benign or malignant nature of the tumor. Blood flow signal is a mandatory item of color Doppler ultrasound, which can see whether there is blood flow signal in the wall of endometrial polyps, uterine fibroids, and ovarian cysts. Generally speaking, the less blood flow signal, the better, and the blood flow signal is often described by the resistance to flow, i.e., the S/D ratio. Benign lesions can have abundant or sparse blood flow, and malignant lesions can have abundant blood flow or show a lack of blood supply, so the blood flow signal does not indicate benign or malignant.