All Type Color Doppler USG

Doppler ultrasonography is medical ultrasonography that employs the Doppler effect to generate imaging of the movement of tissues and body fluids (usually blood),[1] and their relative velocity to the 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. Color Doppler or color flow Doppler is the presentation of the velocity by color scale. Color Doppler images are generally combined with grayscale (B-mode) images to display duplex ultrasonography images, allowing for simultaneous visualization of the anatomy of the area.

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.

The Doppler data is displayed graphically using spectral Doppler, or as an image using color Doppler (directional Doppler) or power Doppler (non directional Doppler). This Doppler shift falls in the audible range and is often presented audibly using stereo speakers: this produces a very distinctive, although synthetic, pulsating sound.

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).[2][3][4]