Color Doppler ultrasound of the blood vessels of the extremities is a non-invasive ultrasound examination that looks at the major blood vessels of the extremities to see if there are any blood clots, if there is any obstruction, and if the lumen of the blood vessels is narrowed and open. 1. The ultrasound is used to clarify the condition of the arteries and veins of the extremities, such as the presence of atherosclerotic plaques in the arteries and whether the plaques have caused narrowing or occlusion of the lumen of the blood vessels. 2. Examine the presence of thrombus in the veins, the presence of valvular insufficiency in the veins, the location of the valvular insufficiency, and the degree of valvular regurgitation. 3. Check the blood flow rate in the arteries and veins. If the blood flow rate is found to be significantly faster, and if the blood vessels can be measured directly by ultrasound to determine if the stenosis is severe or not, and the extent of the stenosis is how long it is, in order to determine if there is an obstruction or stenosis. It is helpful for the evaluation of the arteries and veins of the extremities. If there is any discomfort, it is recommended to seek medical attention in time and be examined by a specialized doctor.