Carotid (ka-ROT-id) ultrasound is a painless and harmless test that uses high-frequency sound waves to create pictures of the insides of your carotid arteries.You have two common carotid arteries, one on each side of your neck. They each divide into internal and external carotid arteries.The internal carotid arteries supply oxygen-rich blood to your brain. The external carotid arteries supply oxygen-rich blood to your face, scalp, and neck.