A Doppler ultrasound is a risk-free and pain-free procedure that uses high-frequency sound waves to measure the amount of blood flow through your arteries and veins, usually those that supply blood to your arms and legs. Vascular flow studies detect the abnormal flow within an artery or blood vessel. It helps to diagnose and treat a variety of conditions, including blood clots and poor circulation. A Doppler ultrasound can be used as part of a blood flow study. It can also reveal blocked or reduced blood flow through narrowed areas in the arteries, which could eventually lead to a stroke.