The Doppler sonography is a special variant of the ultrasound examination and enables the blood flow in arteries and veins to be displayed visually and acoustically. The procedure is mainly used to diagnose heart defects or vascular constrictions.
What is Doppler sonography?
Doppler sonography is a special type of sonography, i.e. an ultrasound examination. The Doppler effect makes the blood flow in the blood vessels audible. Together with the so-called B-image sonography and a special color coding, the blood flow can also be visualized.
In Doppler sonography, a distinction can be made between continuous wave Doppler (CW-Doppler), pulsed-wave Doppler (PW-Doppler) and color-coded Doppler sonography. Color-coded Doppler sonography is the most commonly used in practice. They are also known as Angiodynography.
Function, effect & goals
In Doppler sonography, an ultrasound head sends out ultrasound waves at a defined frequency. When this bundle of ultrasonic waves hits a medium such as a blood cell in the blood vessels, the ultrasonic waves are reflected by these structures. The frequency changes depending on how fast or slow the medium is moving. The reflected waves are measured in sound form by a microphone in the ultrasound head.
The results are then evaluated in the sonography device's computer. The flow velocities measured with the ultrasound head are color-coded. Blood flowing towards the transducer is usually shown in red. If the blood flows away from the transducer, it appears blue. The flow velocities can now be read from the various color levels. Light colors stand for higher, dark colors stand for lower flow rates.
This means that a light blue indicates a higher speed than a dark blue. The resulting color Doppler image is superimposed on the so-called B-mode image. The B-mode image is a variant of the normal black and gray ultrasound image. In this way it can be precisely localized which flow velocities prevail in which vessels. The image is displayed in real time so that changes are always displayed up to date. Different pathologies can be revealed with Doppler sonography. In echocardiography, Doppler sonography is used to examine the heart. Above all, the flow conditions in the area of the heart valves are examined here.
In this way, valve defects, so-called insufficiencies or stenoses, can be diagnosed. With valve insufficiency, the heart valve no longer closes properly; with stenosis, it no longer opens properly. Insufficiencies can be recognized in Doppler sonography by the wrong direction of flow. If a valve no longer closes properly, the blood flows back due to the pressure conditions. In the case of a stenosis, sonography shows a higher flow rate in the stenosis. This can be recognized by a light color. If the valve does not open properly, the blood has to be pressed through the narrowed valve. This increases the flow rate.
Carotid sonography examines the carotid arteries, the carotid artery. Here Doppler sonography is particularly helpful in discovering stenoses. The most common cause of carotid stenosis is atherosclerosis. If the stenosis is very pronounced, it can lead to circulatory disorders in the brain or eyes. If thrombi loosen from the vascular appendages, a stroke can be triggered. The Doppler procedure can be used to diagnose the extent of the carotid stenosis. Carotid Doppler sonography is therefore also suitable for assessing the risk of stroke and heart attack.
Doppler sonography is also used to diagnose thrombosis or to assess vascular walls. The procedure is also used in nephrology. The color Doppler helps to find blood vessels in the kidneys. In obstetrics, too, important vessels such as the ductus venosus or the arteria cerebri media can be found more easily with the Doppler device.
Risks, side effects & dangers
Actually, Doppler sonography is a safe procedure. Possible sources of damage are heat generation and so-called cavitation. There is a negative pressure phase in the sound waves sent by the ultrasound device. It can happen that in one of these negative pressure phases in the examined tissue cavities or gas bubbles develop. If the pressure then increases again, these bubbles can collapse and damage the tissue.
This effect is known as cavitation. Cavitations occur particularly frequently in air-filled areas, for example during ultrasound of the lungs or intestines. The occurrence of cavitations can be promoted by the use of ultrasound contrast media. Overall, the risk of cavitation occurring during Doppler sonography is, however, negligible.
How much heat is generated during an ultrasound examination depends on the absorbed sound intensity. Healthy tissue can cope with a temperature increase of up to 1.5 ° C, even in the long term. If the tissue is damaged beforehand, the increase in temperature can possibly worsen the condition.
Since these risks are also known in the clinics and medical practices, the sound intensities are carefully adjusted there, so that a health risk is unlikely. The advantages of Doppler sonography therefore also lie in the low-risk and, above all, painless application. In contrast to X-rays, the patients are also not exposed to any radiation. From an economic point of view, Doppler sonography also has advantages. The acquisition costs for sonography devices are significantly lower than for procedures such as computed tomography or magnetic resonance tomography. In addition, Doppler sonography is the only method that can depict fluid flows.
The disadvantage of Doppler sonography is that there is no standardized training. The results are therefore strongly influenced by the skill and diagnostic skills of the examiner.
