I. Objectives To evaluate the location, extent and severity of the above arterial lesions. Specifically: 1. intima-media thickening and plaque features; 2. arterial stenosis; 3. arterial occlusion; 4. arterial aneurysm, pseudoaneurysm, arteriovenous fistula. Indications 1.Lower limb weakness and coldness. 2.Intermittent claudication, pain, ulceration or gangrene of lower limbs. 3.Weakness or disappearance of arterial pulsation in the lower extremities. 4.Suspected aneurysm, pseudoaneurysm, arteriovenous fistula. 5.Follow-up after lower limb artery surgery or interventional treatment. Contraindications and limitations There is no absolute contraindication. However, the examination may be limited when the corresponding site is cannulated, ulcerated, or fixed in a cast. The iliac artery examination is commonly performed with a 2-5 MHz convex array probe. The lower extremity arteries are commonly examined with a 4-7 MHz line array probe. The distal segment of the superficial femoral artery and the tibiofibular trunk are deeper, so a 2-5 MHz convex array probe can be used if necessary; the distal segment of the anterior tibial artery and the dorsalis pedis artery are more superficial, so a 5-12 MHz line array probe can be used. In order to reduce the interference of intestinal gas to the iliac artery examination, the patient should fast, abstain from water, smoking and chewing gum for more than 8 hours.