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Doppler ultrasonography is medical ultrasonography that employs the Doppler effect to perform medical imaging of the movement of tissues and (usually blood), (1978). 9782225636790, Masson. ISBN 9782225636790 and their relative velocity to the ultrasound probe. By calculating the frequency shift of a particular sample volume, for example, flow in an artery or a jet of blood flow over a heart valve, its speed and direction can be determined and visualized.
Duplex ultrasonography sometimes refers to Doppler ultrasonography or spectral Doppler ultrasonography. Doppler ultrasonography consists of two components: brightness mode (B-mode) showing anatomy of the organs, and Doppler mode (showing blood flow) superimposed on the B-mode. Meanwhile, spectral Doppler ultrasonography consists of three components: B-mode, Doppler mode, and spectral waveform displayed at the lower half of the image. Therefore, "duplex ultrasonography" is a misnomer for spectral Doppler ultrasonography, and more exact name should be "triplex ultrasonography".
This is particularly useful in cardiovascular studies (sonography of the vascular system and heart) and essential in many areas such as determining reverse blood flow in the liver vasculature in portal hypertension.
In spectral Doppler, the y-axis shows the direction and velocity of the flow. Meanwhile, the x-axis (as known as "baseline") shows the flow over time. The gradient at any point on the waveform would therefore shows the acceleration of the flow. In "antegrade" flow, the blood flows according to the normal flow within the circulatory system (e.g. veins flow towards the heart while arteries flows away from the heart). In "retrograde" flow, the flow would reverse (e.g. veins flow away from heart or arteries flow towards the heart). However, "retrograde" flow can be both abnormal or normal. For example, in portal hypertension, there is an abnormal portal venous flow where it flows away from the liver (hepatofugal flow) instead of the normal flow towards liver (hepatopetal flow). In jugular venous pressure waveform of the internal jugular vein, the retrograde "a" waveform is a normal flow due to right atrium contraction. Both antegrade or retrograde flow can be either towards or away from the probe transducer, depending on the position of the probe relative to the blood flow. Blood flow toward the transducer would appear above the baseline while blood flows away from the transducer will appear below the baseline. Waveform of the flow can be classified as: pulsatile (as in arteries), phasic (as in veins), non-phasic (as in diseased veins), and aphasic (no flow). Spectral broadening (thickness of the waveform) increases from large vessels (plug flow) to medium vessels (laminar flow) to small/stenotic/diseased vessels (turbulent flow) due to a larger variety of blood with different ranges of velocities in those with turbulent flow.
Upstream and downstream stenosis refers to the location of the stenotic site relative to the ultrasound probe. Upstream stenosis means the location of stenosis is located before the ultrasound probe. It causes a marked decrease in peak systolic velocity when compared to end-diastolic velocity, causing marked reduction in resistance index. Meanwhile, downstream stenosis is located after the ultrasound probe. Thus, there is only a slight reduction in peak systolic velocity and end-diastolic velocity (where end-diastolic velocity is reduced more than peak systolic velocity), resulting in an increased resistance index.
Power Doppler is a non directional Doppler.
All modern ultrasound scanners use pulsed Doppler to measure velocity. Pulsed wave instruments transmit and receive series of pulses. The frequency shift of each pulse is ignored, however the relative phase changes of the pulses are used to obtain the frequency shift (since frequency is the rate of change of phase). The major advantage of pulsed wave Doppler (PW Doppler) over continuous wave (CW Doppler) is that distance information is obtained (time between transmitted and received pulses multiplied by sound velocity equals distance) and gain correction is applied. The disadvantage of pulsed Doppler is that the measurements can suffer from aliasing. The terms Doppler ultrasound and Doppler sonography have been accepted to apply to both pulsed and continuous Doppler systems, despite the different mechanisms by which the velocity is measured.
There are no standards for displaying color Doppler. Some laboratories show arteries as red and veins as blue, as medical illustrators usually show them, even though some vessels may have portions flowing toward and portions flowing away from the transducer. This results in the illogical appearance of a vessel being partly a vein and partly an artery. Other laboratories use red to indicate flow toward the transducer and blue away from the transducer. Still other laboratories display the Doppler color map in accordance with published data, with red shift representing longer wavelengths (scattered) from blood flowing away from the transducer and blue representing the shorter wavelengths from blood flowing toward the transducer. Because of this confusion and lack of standards, the sonographer must understand the underlying physics of color Doppler and the physiology of normal and abnormal blood flow in the human body (see Red shift). (2025). 9780198506560, Oxford University Press. ISBN 9780198506560
Duplex evaluation is usually done prior to any invasive testing or surgery. (2025). 9780070692015, McGraw-Hill Professional. ISBN 9780070692015 Ultrasound duplex scanning can provide additional information that may guide therapeutic decisions. The location and severity of arterial narrowings and occlusions can be identified. The vascular sonographer can map disease in lower-extremity segments with great accuracy, though duplex scanning is more time-consuming than other lower-extremity arterial studies.
An alternative to Doppler to visualize vessels is B-flow, which digitally highlights weak flow reflectors (mainly red blood cells) while suppressing the signals from the surrounding stationary tissue. It can visualize flowing blood and surrounding stationary tissues simultaneously.
In addition to visualization, ultrasound can also be used in Doppler auscultation (without visual), similar to using an ultrasound baby monitor, to locate clots or other vascular obstructions or collapse by tracing a blood vessel until sound is no longer heard. It is also used to confirm patency of dorsalis pedis arteries when edema or other conditions make manual palpation impractical.
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