Optimizing Doppler Imaging

Flashcards covering the optimization of Doppler imaging, including gain settings, aliasing, wall filters, and the effects of incident angles.

Normal Incidence

A condition where the angle between the direction of flow and the sound beam is $90$ degrees, resulting in a cosine of zero and the absence of a measured Doppler shift or color.

Color Doppler Gain (High)

A setting that, when adjusted to an inappropriately high level, causing color to appear throughout the color box.

Color Confetti

A term used to describe the appearance of color throughout the color box when the color gain is set too high.

Color Doppler Gain (Low)

A setting that causes all color to disappear from the image when set to an inappropriately low level.

Spectral Doppler Gain (High)

A setting that, when increased to an excessive level, results in gray scale noise appearing throughout the spectrum.

Spectral Doppler Gain (Low)

A setting where all gray scale, including the meaningful Doppler spectrum and noise, disappears from the image.

Aliasing (Color Flow)

An artifact that appears when colors that touch each other on the image go around the outside of the color map, often appearing as a direct change from red to blue or vice versa.

Flow Reversal

A color transition (such as red to black to blue) that passes through the center of the color map, indicating a change in direction rather than an artifact.

Velocity Scale (Increase)

The most effective technique to eliminate aliasing on a color flow image, which simultaneously decreases sensitivity to slow flows.

Wall Filter

A control that selectively eliminates low frequency Doppler shifts near the baseline caused by slowly moving structures such as venous blood flow or vibrating tissues.

Ghosting Artifact

An artifact along the vessel wall (such as the deeper wall of an artery) that can be eliminated by increasing the wall filter.

Autocorrelation

The method used by color Doppler to process the Doppler signal.

Sensitivity to Slow Flow

The ability of the system to detect low velocities, which is reduced when the velocity scale is increased, causing slow flows to be assigned the black color in the center of the color map.