A carotid artery Doppler is a special type of ultrasound device that relies on the Doppler effect to determine the amount of blood flow through the carotid arteries. The carotid arteries are two arteries that reside in the front portion of the neck that are responsible for carrying oxygenated blood from the heart to the neck and the brain. Generally, a carotid artery Doppler is used to detect stenosis, or narrowing, in these arteries. It can also be used to check for potential blockages, detect a split in the artery wall, and verify the location of a stent, which is a device used to maintain blood flow.
An ultrasound machine like the carotid artery Doppler uses sonography to obtain an image of the carotid arteries. Sonography refers to the process of exposing the body to sound waves at very high frequencies and using the reflections of these waves to produces pictures of body organs. Generally, the sound waves are emitted through a hand-held wand that is placed directly onto the skin. The waves penetrate the skin and upon hitting an organ or other internal structure, they bounce back. Then, a device inside the ultrasound machine known as the transducer determines the distance of the object and whether it contains fluid, air, or is solid, and it constructs a picture of the image, which is subsequently viewable on a monitor.
In order to evaluate how efficiently blood is flowing through the carotid arteries, a carotid artery Doppler relies on what is known as the Doppler effect. The Doppler effect, which is named for the Austrian physicist Christian Doppler, refers to the alteration in the wavelength and frequency of sound waves and other types of waves for an observer who is moving relative to the location that the wave originated. Generally, when waves move towards the observer, distance between waves shortens and the frequency at which waves occur increases. The opposite occurs as waves move away from an observer.
How much the frequency and wavelength of sound waves is altered depends on how fast the object is moving. Measuring the change in wavelength and frequency can determine how fast the object is moving. This is how the carotid artery Doppler evaluates blood flow. It uses the change in wavelength to determine how fast blood is flowing through the arteries. Knowing the speed of the blood flow then allows the user to determine whether or not the blood is flowing through the arteries at normal levels.