The pixel is a picture element. Pixels do not have a fixed size; their diameters are generally measured in micrometers (microns). Although the pixel is not a unit of measurement itself, pixels are often used to measure the resolution (or sharpness) of images.

Variance is the modification of Doppler frequencies within each pixel during a pulse packet with color Doppler flow imaging. Variance is mapped to the color green and is used to detect turbulence. At low variance (laminar flow) pixels within each range gate are encoded in red or blue according to flow direction. At high variance (turbulent flow) a percentage of pixels within each range gate are encoded with green according to the degree of spectral broadening.

A voxel is a volume element (volumetric and pixel) representing a value in the three dimensional space, corresponding to a pixel for a given slice thickness. Voxels are frequently used in the visualization and analysis of medical data. The ultrasound pixel intensity is proportional to the signal intensity of the appropriate voxel.

See also Slice Thickness Artifact.

The color priority determines which signal of B-mode and Doppler, detected from the same location will be displayed in a given pixel. Low color priorities will allow solid tissue to conceal Doppler shifts at the same location; a high priority ensures that color will overwrite the gray scale image.
Also called color-echo write priority or angio write priority.

See also Directional Indicators.

Color assignments can be switched on any ultrasound system and are used as directional indicators. The colors of red and blue indicates flow direction in color Doppler.
Red is encoded to represent flows toward the transducer.
Blue pixel encoding is used to depict flows away from the transducer.

See also Directional Color Power Doppler.