Colour Doppler is a duplex ultrasound to see how the blood moves through our arteries and veins. The test combines traditional ultrasound with Doppler ultrasonography. Regular Ultrasound uses sound waves that are bounce off from blood vessels to create pictures. Doppler looks at how sound waves are reflected from moving objects, such as blood. It is the duplex ultrasound of abdomen examines blood vessels and blood flow in the abdominal area. It is the renal duplex ultrasound examine the kidneys.