If the blood flow signal is not seen in the blood vessels, it usually suggests that the blood vessels are occluded, and the prognosis is generally poor. If no blood flow signal is detected in the veins of the lower extremities, suggesting venous thrombosis of the lower extremities, the patient will often experience swelling and pain in the lower extremities, accompanied by sunken edema, requiring anticoagulant therapy, and if necessary, inferior vena cava filter implantation for prevention of pulmonary artery embolism. If the arteries of the lower limbs are not detected, suggesting that the distal lower limb artery occlusion, patients often have resting pain in the lower limbs, aggravated by activity, accompanied by coldness and numbness of the affected limbs, the dorsal arterial pulses disappeared, and need to perform vein stent implantation or bypass grafting to improve the blood flow of the affected limb distal.