![]() 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). Pulsed wave instruments transmit and receive series of pulses. ![]() Power Doppler is a non directional Doppler.Īll modern ultrasound scanners use pulsed Doppler to measure velocity. 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. Meanwhile, downstream stenosis is located after the ultrasound probe. It causes a marked decrease in peak systolic velocity when compared to end-diastolic velocity, causing marked reduction in resistance index. Upstream stenosis means the location of stenosis is located before the ultrasound probe. Upstream and downstream stenosis refers to the location of the stenotic site relative to the ultrasound probe. 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. 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). Blood flow toward the transducer would appear above the baseline while blood flows away from the transducer will appear below the baseline. 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. In jugular venous pressure waveform of the internal jugular vein, the retrograde "a" waveform is a normal flow due to right atrium contraction. 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). However, "retrograde" flow can be both abnormal or normal. veins flow away from heart or arteries flow towards the heart). ![]() In "retrograde" flow, the flow would reverse (e.g. veins flow towards the heart while arteries flows away from the heart). In "antegrade" flow, the blood flows according to the normal flow within the circulatory system (e.g. The gradient at any point on the waveform would therefore shows the acceleration of the flow. Meanwhile, the x-axis (as known as "baseline") shows the flow over time. In spectral Doppler, the y-axis shows the direction and velocity of the flow. ![]() Any sudden changes in direction of blood flow produces audible sounds on the ultrasound machine. Meanwhile, spectral Doppler not only shows the direction of blood flow, it also shows the phases (pulsatility) and acceleration of the blood flow. Operation Duplex scan of the common carotid arteryĬolour Doppler shows the direction of the blood flow in red or blue (either towards or away from the transducer). 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. Therefore, "duplex ultrasonography" is a misnomer for spectral Doppler ultrasonography, and more exact name should be "triplex ultrasonography". Meanwhile, spectral Doppler ultrasonography consists of three components: B-mode, Doppler mode, and spectral waveform displayed at the lower half of the image. 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. 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.ĭuplex ultrasonography sometimes refers to Doppler ultrasonography or spectral Doppler ultrasonography. Spectral duplex scan of the common carotid arteryĭoppler ultrasonography is medical ultrasonography that employs the Doppler effect to perform imaging of the movement of tissues and body fluids (usually blood), and their relative velocity to the probe. ![]()
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