Vascular ultrasound precautions are: 1. to clarify the anatomical location of the lower limb vessels and the names of the branches of the vessels at all levels. 2. to achieve an orderly examination, generally from top to bottom, starting from the groin area to the dorsum of the foot. 3. when probing the deep arteries, pay attention to whether there is thickening and roughness of the vessel wall, whether sclerosis has occurred, whether sclerotic plaques have formed, whether plaques have caused luminal stenosis, and if there is stenosis, measure the degree of stenosis, indicate the location of the stenosis and the name of the stenosed vessel, and the length of the stenosis. If there is stenosis, the degree of stenosis should be measured, the location of the stenosis and the name of the stenotic vessel, and the length of the stenosis, and whether there is thrombus formation in the lumen should be observed, and the location and size of the thrombus should be indicated. 4.When probing deep veins, attention should be paid not to press the probe forcefully to avoid the deformation of the vein and affect the observation. 5.When exploring the superficial veins of the lower limbs, the internal diameter of the lumen should be measured to see if there are varicose veins. Because ultrasound cannot detect the direction and speed of blood flow in the vessels and cannot observe whether there is regurgitation in the valves, ultrasound is also used when necessary.