In industrialized countries, diseases of the cerebral vessels (e.g., apoplexy – stroke) rank third in mortality statistics after heart disease and cancer. In Doppler sonography for stroke risk assessment (synonym: stroke check), the neck vessels (carotids and the vertebral arteries) and, if necessary, the large intracranial vessels are examined. In this way, blood flow velocities in the vessels and the structure of the vessel walls (plaque changes such as ulcerations (ulcerations); stenoses (vessel constrictions) and intima-media thickness (IMT)) can be assessed or determined. Doppler sonography (synonyms: Doppler effect sonography, Doppler echography) is a medical imaging technique that can dynamically visualize fluid flows (primarily blood flow). It is used to assess blood flow velocity and, in cardiology, to diagnose heart and heart valve defects. Especially in the case of pathological (diseased) vascular changes, the Doppler sonographic examination represents the basis of the diagnostic procedure, since both the velocity distribution in the respective vessel section is assessed and an exact representation of the flow direction can be made. Furthermore, Doppler sonography makes it possible to reproduce the temporal change in the velocity of the blood flow. The factors thus obtained can then be used to calculate the volume flow rate and the pathophysiologically important flow resistances.
Indications (areas of application)
- Obesity (overweight)
- Apoplexy (stroke) or transient ischemic attack (TIA) – sudden onset neurological disorder that resolves within 24 hours).
- Atherosclerosis (arteriosclerosis, hardening of the arteries).
- CRP elevation – increased C-reactive protein.
- Diabetes mellitus
- Smokers
- Cardiac arrhythmia (atrial fibrillation)
- Hypercholesterolemia (lipid metabolism disorder)
- Hyperhomocysteinemia
- Hypertension (high blood pressure)
- Physical inactivity
- Coronary artery disease (CAD, coronary artery disease).
- Myocardial infarction (heart attack) risk or condition after myocardial infarction.
- Periodontitis (disease of the periodontium).
- Peripheral arterial occlusive disease (pAVK)
- Psoriasis (psoriasis)
- Other individual health risks
The procedure
Doppler sonography is based on the principle that ultrasound waves are emitted at a defined frequency into the tissue, where they scatter on circulating erythrocytes (red blood cells). Due to this scattering, a portion of the ultrasound waves returns to the transducer, which thus serves on the one hand as a transmitter and on the other hand as a receiver of the sound waves. The erythrocytes thus act as a boundary surface at which the sound waves are reflected, so that a frequency increase occurs when the distance between the transducer and the boundary surface decreases and the frequency decreases when the distance increases. However, the so-called Doppler effects occur not only in flowing blood, but also in other moving organic structures, such as vessel walls. Doppler sonography is divided into several techniques:
- Single-channel Doppler techniques: In this method, a single beam of sound is emitted by the Doppler system, so that the resulting data arise solely from the section of vascular structure through which the beam passes.
- Continuous-wave (CW) Doppler sonography: a subset of single-channel Doppler techniques, this system represents the simplest method of collecting continuous blood flow data over the entire depth of ultrasound penetration. Each transducer has separate acoustic elements for sound transmission and reception. Continuous information acquisition is made possible by the fact that the transmitter and receiver in the transducer operate in parallel and continuously side by side. However, spatial assignment is not possible with this method. However, the advantage of this method is that the determination of high flow velocities is possible.
- Pulsed-wave (PW) Doppler sonography: as a further subgroup of the single-channel Doppler methods, a spatially selective velocity measurement is possible with this system in contrast to CW Doppler sonography.In pulsed Doppler mode, an electronic gate is generated to measure the flow velocity of erythrocytes passing through the gate at a defined depth in the tissue. Unlike the CW Doppler method, the information is transmitted via pulses and not continuously.
- Multichannel Doppler techniques (synonyms: Color Doppler sonography, color-coded Doppler sonography, color-coded duplex sonography; combination of B-scan with PW Doppler/Pulse Wave Doppler): In this technique, as in CW Doppler sonography, the sound transmitter and the sound receiver are located as separate structures in the transducer. However, the difference is that a large number of transmitters and receivers are located in each transducer. The transmission and reception of ultrasound waves do not occur simultaneously, allowing the many sound beams to gather information from a three-dimensional cross-sectional image. All multichannel systems operate in pulsed Doppler mode. The collection of information is limited by the limited number of evaluation channels in the Doppler sonograph. The large number of sound waves ensures accurate localization of information sources. Due to the functional properties of the method, it is used to estimate possible flow turbulence with the help of color coding, where different flow velocities can be represented in shades of red and blue. The turbulence itself is represented in green.
Doppler and duplex sonography are two complementary special ultrasound techniques. In pure Doppler sonography (D-mode procedure), the blood flow within the blood vessels is assessed. Stenoses (constrictions ) from approx. 40-50% can be detected and their extent determined. Duplex sonography (B-mode procedure) assesses the course of the blood vessels, the vessel caliber and the nature of the intima-media thickness (IMT). Wall thickness and any arteriosclerotic plaques (deposits) present are measured. The measured values determined in this way are used for direct comparison during further follow-up examinations. The intima-media thickness (synonyms: IMD; intima-media-thickness – IMT) of the common carotid artery is determined bilaterally (carotid intima-media thickness test (CIMT)). Color-coded duplex sonography is particularly useful for estimating possible flow turbulence and thus for assessing stenosis-
Ultrasound contrast agents based on the technique of so-called microbubbles can be used to amplify the ultrasound waves in Doppler sonography. Microbubbles are micrometer-sized gas bubbles that amplify the ultrasound signal because they are capable of completely reflecting sound waves. In contrast to native Doppler sonography, computed tomography (CT) and magnetic resonance imaging (MRI) allow visualization of the capillary flow area. With the use of microbubbles, it is also possible in Doppler sonographic examinations to determine the flow velocity of blood in the capillary bed by measuring and evaluating the bursting of the gas bubbles, which is caused by the occurrence of sound waves. The duration of the examination is approximately 20 minutes. Doppler sonography of the carotid artery (carotid artery) on both sides shows stenosis (narrowing) due to plaques, thrombi or calcifications in time. Doppler sonography is a non-hazardous examination of your carotids (neck arteries) and the flow characteristics of your blood. In the event of constriction of the carotids, preventive therapy can thus be carried out in good time. Doppler sonography serves your protection against a stroke and thus your preventive health care.
