UP Ch 5 Key terms

Autocorrelation

A rapid technique, used in most color-Doppler instruments, to obtain mean Doppler-shift frequency.

Baseline shift

Movement of the zero Doppler-shift frequency or zero flow speed line up or down on a spectral display.

Bernoulli effect

Pressure reduction in a region of high-flow speed.

Bidirectional

Indicating Doppler instruments capable of distinguishing between positive and negative Doppler shifts (approaching and receding flow).

Clutter

Noise in the Doppler signal that generally is caused by high-amplitude, Doppler-shifted echoes from the heart or vessel walls.

Color-Doppler display

The presentation of two-dimensional, real-time Doppler-shift information in color superimposed on a real-time, gray-scale, anatomic, cross-sectional image. Flow directions toward and away from the transducer (i.e., positive and negative Doppler shifts) are presented as different colors on the display.

Compliance

Distensibility; nonrigid stretchability of vessels.

Continuous-wave Doppler

A Doppler device or procedure that uses continuous-wave ultrasound.

Cosine

The cosine of angle A in Figure C.1 is the length of side b divided by the length of side c. Abbreviated cos.

Disturbed flow

Flow that cannot be described by straight, parallel streamlines.

Doppler angle

The angle between the sound beam and the flow direction.

Doppler effect

A change in frequency caused by reflector motion.

Doppler equation

The mathematical description of the relationship between the Doppler shift, frequency, Doppler angle, propagation speed, and reflector speed.

Doppler-power display

Color-Doppler display in which colors are assigned according to the strength (amplitude, power, intensity, energy) of the Doppler-shifted echoes.

Doppler shift

Reflected frequency minus incident frequency; the change in frequency caused by motion.

Doppler spectrum

The range of frequencies present in Doppler-shifted echoes.

Duplex instrument

An ultrasound instrument that combines gray-scale sonography with pulsed Doppler and, possibly, continuous-wave Doppler.

Eddies

Regions of circular flow patterns present in turbulence.

Ensemble length

Number of pulses used to generate one color-Doppler image scan line.

Fast Fourier transform

Digital computer implementation of the Fourier transform.

Filter

An electric circuit that passes frequencies within a defined range.

Flow

To move in a stream; volume flow rate.

Fluid

A material that flows and conforms to the shape of its container; a gas or liquid.

Frequency spectrum

The range of Doppler-shift frequencies present in the returning echoes.

Gate

A device that allows only echoes from a selected depth (arrival time) to pass.

Hue

The color perceived based on the frequency of light.

Inertia

Resistance to acceleration.

Laminar flow

Flow in which fluid layers slide over each other in a smooth, orderly manner, with no mixing between layers.

Luminance

Brightness of a presented hue and saturation.

Parabolic flow

Laminar flow with a profile in the shape of a parabola.

Phase quadrature

Two signals differing by one-fourth of a cycle.

Plug flow

Flow with all fluid portions traveling with the same flow speed and direction.

Poise

Unit of viscosity.

Poiseuille equation

The mathematical description of the dependence of volume flow rate on pressure, vessel length and radius, and fluid viscosity.

Priority

The gray-scale echo strength below which color-Doppler information is shown preferentially on a display.

Pulsatile flow

Flow that accelerates and decelerates with each cardiac cycle.

Pulsed Doppler

A Doppler device or procedure that uses pulsed-wave ultrasound.

Range gating

Selection of the depth from which echoes are accepted based on echo arrival time.

Resistance

Pressure difference divided by volume flow rate for steady flow.

Sample volume

The anatomic region from which pulsed Doppler echoes are accepted

Saturation

The amount of hue present in a mix with white.

Spectral analysis

Separation of frequencies in a Doppler signal for display as a Doppler spectrum; the application of the Fourier transform to determine the frequency components present in a Doppler signal.

Spectral broadening

The widening of the Doppler-shift spectrum; that is, the increase in the range of Doppler-shift frequencies present that occurs because of a broadened range of flow velocities encountered by the sound beam. This occurs for disturbed and turbulent flow.

Spectral-Doppler display

The presentation of Doppler information in a quantitative form of Doppler shift versus time. Visual display of a Doppler spectrum.

Spectrum analyzer

A device that derives a frequency spectrum from a complex signal.

Stenosis

Narrowing of a vessel lumen.

Streamlines

A line representing the path of motion of a particle of fluid.

Turbulence

Random, chaotic, multidirectional flow of a fluid with mixing between layers; flow that is not laminar.

Variance

Square of standard deviation; one of the outputs of the autocorrelation process; a measure of spectral broadening (i.e., spread around the mean).

Viscosity

Resistance of a fluid to flow.

Volumetric flow rate

Volume of fluid passing a point per unit of time (i.e., per second or minute).

Wall filter

An electric filter that passes frequencies above a set level and eliminates strong, low-frequency Doppler shifts from pulsating heart or vessel walls or tissue motion.

Window

An anechoic region appearing beneath echo frequencies presented on a Doppler spectral display

pressure gradient

also known as pressure differential, The greater the pressure difference, the greater the flow rate

bruits

related to stenosis, sounds produced by turbulence that can be heard with a stethoscope

occlusion

Condition where no flow is present due to stenosis