Duplex systems often combine a pulsed Doppler with a spectral display and a real time imaging system. A duplex scanner has usually an imaging transducer or a separate transducer used to collect continuous wave or pulsed Doppler signals, either simultaneously with imaging or sequentially.
(CD) Color Doppler is an ultrasound imagingmode, which visualizes the presence, direction and velocity of flowing blood in a wide range of flow conditions. It provides an estimate of the mean velocity of flow within a vessel by color coding the flow and displaying it superimposed on the 2Dgray scale image. The flow direction is arbitrarily assigned the color red or blue, indicating flow toward or away from the transducer.
Color (colour, Brit.) Doppler ultrasound is capable of evaluating a wider area than other Doppler modes than for example Duplex or power Doppler, and therefore makes it less likely to miss flow abnormalities. It is also easier to interpret. Color flow is not as precise as conventional Doppler and is best used to scan a larger area and then use conventional Doppler for detailed analysis at a site of potential flow abnormality.
Adjustments for color Doppler in case of too much color:
Compound B-mode imaging takes different forms and refers to different methods of creating the ultrasound image.
Real-time compound ultrasound improves the image quality of B-mode scanning by combining ultrasound information obtained from multiple angles. The used averaging process of compound B-mode reduces artifacts and improves the representation of true image data.
B-mode images and Dopplermode images (see also Duplex) can be compounded on the display to improve the visualization of the anatomical relationships between vessels and the surrounding tissues.
Doppler ultrasound is a medical imaging technique for calculating the relative velocity between two points by measuring the frequency shift of a sound wave transmitted from one point to the other, based on the Doppler effect. Continuous or pulsed Doppler is frequently used to examine cardiovascular blood flow. The combination of routine 2D-mode and Doppler ultrasound allows a complete evaluation of the heart's anatomy and function (including the fetal heart). See also Doppler Fluximetry in Pregnancy.
Doppler ultrasound depends on the fact that if a moving object reflects the ultrasound waves, the echo frequencies are changed. A higher frequency is created if the object is moving toward the probe//transducer and a lower frequency if it is moving away from it. How much the frequency is changed depends upon how fast the object is moving. Doppler ultrasound shows the different rates of blood flow in different colors on a monitor in real time.
The major Doppler parameters are the peak systolic velocity and the end-diastolic velocity. The peak systolic velocity ratio compensates the variability between different patients and instrumentations.