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.