<unk>  is medical<unk>  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. 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<unk>  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.
Doppler ultrasonography
Laser Doppler imaging
Intravascular fluorescence
Doppler echocardiography
Tissue Doppler echocardiography
Intravascular ultrasound
Digital variance angiography
Intravascular imaging