(AI) This index is the ratio between the acceleration of the Doppler spectral waveform and the relative peak systolic velocity. The systolic acceleration is determined by the change in distance between the begin of systolic flow and the peak systolic velocity (cm/sec), divided by the acceleration time (AT - time interval from the onset of flow to the initial peak).
The acceleration index is reported in frequency units as KHz/sec or velocity units as cm/sec2.

(CDI) Color Doppler imaging depicts the mean frequency shifts of the Doppler signal. Color [colour, Brit.] Doppler imaging is a method for visualizing direction and velocity of movement, such as of blood flow within the cardiac chambers or blood vessels. The flow direction and velocity information gathered by Doppler ultrasonography is color coded onto a gray scale cross-sectional image. The sensitivity of Doppler ultrasound is increased in conjunction with the use of vascular contrast agents.
Direction and blood flow velocity are coded as colors and shades:
Red - flow coming nearer to the probe.
Blue - flow coming away of the probe.

See also Bi-directional Illumination, Color Map.

A flat velocity profile in large vessels is termed plug flow, indicating that all or most of the blood is flowing at a single velocity per time unit.

See also Blood Flow Velocity.

(RI) The resistive index is a measure of resistance to arterial flow and is calculated from the power Doppler arterial waveform.
The equation of this index is:
RI = (peak systolic velocity - end diastolic velocity) : peak systolic velocity

The Bernoulli effect describes the reduction in pressure that occurs with an increase in velocity of fluid flow.

See also Bernoulli Equation, and Maximum Velocity.