What tests show blood flow?

• Doppler ultrasound test - Uses high-frequency sound waves to detect blockages in the carotid artery . A Doppler probe or instrument capable of generating ultrasound waves is placed on the neck very near to the carotid artery. Ultrasound waves from the probe travel through the neck and bounce off the moving blood cells. The reflected sound wave, now returning to the probe at a different frequency, is then detected by the same probe. The change in frequency of the sound waves relates to the speed of the blood cells and thus the blood flow.


• Carotid phonoangiography - A sensitive microphone is placed on the neck, very close to the carotid artery, to record sounds. Ordinarily, in a normal artery, blood flows in a smooth and controlled manner. However, the presence of blockages, such as those caused by atherosclerosis, causes the blood flow to become turbulent. This turbulent blood flow can create a sound, called a bruit , that can be detected and registered by the microphone. A bruit indicates a blockage in the carotid artery and is cause for more tests.


• Digital subtraction angiography (D.S.A.) - Gives an image of the brain's major blood vessels. A thin plastic tube (a catheter) is inserted into a major artery of the leg and navigated through the body's major vessels until it reaches the brain's blood vessels. A contrast dye is injected through the catheter and allowed to circulate in the bloodstream. At that point, an X-ray machine quickly takes a series of pictures of the head and neck. The images track the movement of the contrast dye as it moves through the brain's blood vessels. This imaging technique lets the doctor identify and localize the source of stroke.