Color ultrasound, or color Doppler flow imaging, abbreviated as CDFI, refers to the processing of the obtained Doppler information, and through color grayscale coding, the direction of blood flow and the magnitude of velocity are identified by different colors and brightnesses, respectively, and superimposed on the B-mode ultrasound sonogram. The color ultrasound blood flow is characterized by the color representing the direction of blood flow, i.e., red representing the direction of blood flow toward the probe and blue representing the direction of blood flow away from the probe; the brightness of the hue indicates the speed, i.e., the brighter the hue indicates the higher the speed and the darker the hue indicates the lower the speed. Color Doppler ultrasound has the advantages of both two-dimensional ultrasound structural images and provides rich information on hemodynamics at the same time, and has a wide range of clinical applications. Its main advantages are: 1. It can quickly and visually display the two-dimensional planar distribution state of blood flow in real time. 2. It can show the running direction of blood flow. 3. It can identify arterial and venous vessels. 4. It can identify vascular and non-vascular lesions. 5. It can understand the nature of blood vessels. 6. It can measure blood flow velocity, acceleration, acceleration time, resistance index, pulsatility index, as well as regurgitant area, regurgitant flow velocity and differential pressure, etc.