A doppler (or dop) is a type of ultrasound that uses sound waves to look at blood flow in veins and arteries. It works by sending out high-frequency sound waves that bounce back, showing the blood moving through the vessels.
It is used to help diagnose conditions like blood clots, blocked arteries, narrowed arteries, heart valve defects or decreased blood circulation in leg veins. This noninvasive test is performed with a small, hand-held device against the skin in the area being visualized. It is also known as Doppler ultrasound.