What is a doppler ultrasound test? . A Doppler ultrasound is a special type of ultrasound test that uses sound waves to measure blood flow through your arteries and veins. What it does Shows how fast blood is moving. Shows direction of blood flow. Detects blockages, narrowing, or abnormal flow patterns. Helps identify clots, reduced blood supply, or valve problems. Common uses Checking for heart blockages and reduced blood flow in leg arteries. Detecting DVT, varicose veins Assessing carotid art