The difference between Doppler and color ultrasound is that color ultrasound can observe relatively stationary organs, while Doppler can observe dynamic organs. When examining blood vessels, color ultrasound can observe the hierarchical structure of the vessel wall, measure the thickness of the vessel wall and the inner diameter of the lumen, and can observe whether the lining of the vessel wall is thickened and whether sclerotic plaque is formed, and can observe whether the lumen of the vessel is dilated and narrowed. Doppler can show the blood flow in the lumen based on the ultrasound observation, and the blood flow toward the direction of the probe is shown in red, and the blood flow away from the probe is shown in blue. Doppler can measure the velocity of blood flow in the lumen and can distinguish between arteries and veins. Especially when examining organs, the combination of ultrasound and Doppler together allows observation of lesions in the organs. If a substantial occupancy is observed in the organ, the combination of ultrasound and Doppler can observe the size and shape of the nodule, and also observe whether there is a vascular supply inside, which provides a great help to the clinician’s treatment.