Artery and vein. Coloured doppler ultrasound (angiodynography) scan showing healthy blood flow in a vein (blue) and artery (red) of the leg. Oxygenated blood is pumped out of the heart and travels through arteries, deoxygenated blood flows back to the heart through veins. Angiodynography uses the Doppler effect. This causes blood flowing towards the detector to reflect sound waves at a different frequency from blood flowing away from it. This allows the blood in the veins and arteries to be differentiated.
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