(CD) Color Doppler is an ultrasound imaging mode, which visualizes the presence, direction and velocity of flowing blood in a wide range of flow conditions. It provides an estimate of the mean velocity of flow within a vessel by color coding the flow and displaying it superimposed on the 2D gray scale image. The flow direction is arbitrarily assigned the color red or blue, indicating flow toward or away from the transducer.
Color (colour, Brit.) Doppler ultrasound is capable of evaluating a wider area than other Doppler modes than for example Duplex or power Doppler, and therefore makes it less likely to miss flow abnormalities. It is also easier to interpret. Color flow is not as precise as conventional Doppler and is best used to scan a larger area and then use conventional Doppler for detailed analysis at a site of potential flow abnormality.

Adjustments for color Doppler in case of too much color:
Adjustments for color Doppler in case of not enough color:
See also Color Power Doppler, Autocorrelation, Color Priority, Triplex Exam and Color Saturation.

(Doppler look angle) The angle of incidence is the angle at which the ultrasound beam strikes an interface, or the angle at which the Doppler beam intersects the blood flow. Doppler signals are best obtained at angles of 60° or less.

See also Snells Law.

In 3D ultrasound (US) several 2D images are acquired by moving the probe across the body surface or rotating inserted probes. 3D-mode uses the same basic concept of a 2D ultrasound but rather than take the image from a single angle, the sonographer takes a volume image. The volume image that is displayed on the screen is a software rendering of all of the detected soft-tissue combined by specialized computer software to form three-dimensional images.
The 3D volume rendering technique (VR) does not rely on segmentation (segmentation techniques are difficult to apply to ultrasound pictures) and makes it possible to obtain clear 3D ultrasound images for clinical diagnosis. A 3D ultrasound produces a still image. Diagnostic US systems with 3D display functions and linear array probes are mainly used for obstetric and abdominal applications. The combination of contrast agents, harmonic imaging and power Doppler greatly improves 3D US reconstructions.

3D imaging shows a better look at the organ being examined and is used for:

Fusion 3D imaging methods for generating compound images from two sets of ultrasound images (B-mode and Doppler images) enable the observation of the structural relationships between lesions and their associated blood vessels in three dimensions (maximum intensity projection).