Color Doppler

Doppler ultrasound and imaging are focused on the visualization and 
measurement of blood flow in the body. This is a technological 
achievement because, until recently, the received echoes from the 
acoustic scatterting from regions of blood, such as those in the 
chambers of the heart, were at levels so low that they could not be seen 
or appeared as black in an ultrasound image. Even when blood 
circulation, called color flow imaging, as well as precise continuous 
wave, and pulsed wave Doppler measurements of blood flow, are 
routine on imaging systems. In this specialized area of ultrasound, 
interrogating beams are sent repeatedly in the same direction and are 
compared to each other to determine the movement of blood scatterers 
over time. All the usual physics of ultrasound apply, including beam 
directivity, transducer bandwidth, absorption, and the scattering 
properties of the tissue (blood). Doppler detection is a blend of physics 
and specialized signal processing techniques required to extract, 
process, and display weak Doppler echoes. Doppler techniques 
provide critical diagnostic information noninvasively about the fluid 
dynamics of blood circulation and abnormalities.