Color-coded Doppler sonography
The color-coded Doppler sonography (abbr .: CDS ; Synonym: Angiodynographie in short, the color Doppler ) is a form of ultrasound , by which the direction of blood flow is illustrated with respect to the transducer colored in red or blue. In this way, the blood flow in arteries can be differentiated from that in the veins and, ultimately, conclusions can be drawn about the presence and extent of circulatory disorders . In addition, the color Doppler helps to find small vessels that cannot be shown in the B-image , and also to assess functional disorders of the heart valves and defects in the heart muscle in echocardiography .
Physical basics
The Doppler effect changes the frequency of sound waves when they are reflected or scattered by a moving object. This effect is used in the color Doppler. The transducer emits a tone of a defined frequency (usually several MHz ). This tone is reflected by the irradiated medium (e.g. blood ) and the frequency changes according to the Doppler effect. This reflected sound is measured by a microphone in the transducer and then evaluated in the computer. The measured speeds are color- coded . Flow towards the transducer is usually shown in red, and flow away from the transducer in blue. The different speeds are displayed in different color levels; For example, a light red represents a higher speed than a dark red. The color pixel represents the average speed of a volume and is calculated with the help of autocorrelation . The color Doppler image is superimposed on the B-mode image and displayed to the examiner on a screen. This happens in real time .
Medical applications
The color Doppler helps to find anatomical structures and pathologies .
The color Doppler is used clinically in the following areas:
- Echocardiography - examination of the heart , in particular the flow conditions around the valves to detect stenoses and insufficiencies. Insufficiencies are recognized at the flow "in the wrong direction"; Stenoses (narrowing) on the lighter color because of the higher velocities within the stenosis.
- Carotid sonography - examination of the carotid arteries ( common , internal and external carotid arteries ); a stenosis can also be detected here. The color Doppler helps to localize the stenosis in order to then quantify it with the help of the PW Doppler.
- Angiology - representation of the veins and arteries . Here, too, the conditions on the vessel wall ( plaques , stenoses, etc.) can be better represented. In the diagnosis of deep vein thrombosis (DVT) (in the case of pelvic vein thromboses and thromboses in the area of the distal lower leg veins ), color-coded duplex sonography can be superior to the primary compression ultrasound (KUS). Otherwise, the color Doppler does not significantly increase the already high diagnostic accuracy of the KUS and is only a supplementary examination. For examiners with more than three months of sonographic experience, the FKDS can be performed on average in less than 20 minutes.
- Nephrology : The color Doppler helps to find the vessels in the kidneys in which the resistance index is measured with the help of the PW Doppler .
- Obstetrics: Ductus venosus and arteria cerebri media can be found more easily. Doppler sonography is not completely risk-free during pregnancy. It can lead to a biologically significant increase in temperature in the ultrasound tissue. Due to the potential risk of damage to cerebral structures, Doppler sonography is limited to the second half of pregnancy and to cases of certain indications (such as suspected fetal malformations or abnormal heart rate patterns). When using Doppler sonography, a careful balance must therefore be made between the benefits and risks of the examination.
criticism
A numerical evaluation of the color representation as well as the processed raw data does not provide an evident decision-making basis for a final differentiation of the tissue properties with regard to the dignity (malignant tumor or benign tumor). The automatic or even just the visual qualification of tissue, for example when it comes to metastasis, is not possible. Such a qualification can instead be done with a needle biopsy.
However, the differentiation according to physical parameters and the corresponding coloration provide a good assessment of the localization, in particular the spatial distribution of tissue with the same properties.
Further developments
The following developments provide additional parameters for tissue differentiation:
- Power Doppler: The Power Doppler does not represent the speed and direction, but the energy of the movement.
- Tissue Doppler (tissue Doppler): This method not only the movements of the blood, but also of the can tissue shown and quantified are.
Individual evidence
- ^ B. Widder, M. Görtler: Doppler and duplex sonography of the arteries supplying the brain. Springer, 2004, ISBN 3-540-02236-8 .
- ↑ J. Fernandez Sanchez et al.: Determination of the duration of an FKDS examination for the diagnosis of a leg vein thrombosis. ( Memento from June 12, 2008 in the Internet Archive )
- ↑ Horst Steiner, Karl Theo M. Schneider (ed.): Doppler sonography in obstetrics and gynecology. 3. Edition. ISBN 3-642-20938-6 , pp. 72 f.
- ↑ Preoperative assessment of the condition (PDF; 5.0 MB).