This test can show your physician if you have any blockages in your carotid arteries. If so, you may be at risk for a future stroke. In this painless test, a technician holds a small ultrasound probe to your neck. The probe emits high-frequency sound waves that bounce off of blood cells and blood vessels to show blood flow and problems with the structure of blood vessels. No special preparation is required for this test, and it can be performed within 20-30 minutes.