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

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 display that is presented in color

compliance

Distensibility; nonrigid stretch-ability of vessels

continuous wave doppler

a Doppler device or procedure that used continuous wave ultrasound

cosine

the length of side B divided by the length of side C

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 math 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

Doppler shift

reflected frequency minus incident frequency, the change in frequency caused by motion

Doppler spectrum

the range of freq present in Doppler shifted echoes

duplex instrument

an ultrasound instrument that combines gray scale sonography with pulsed Doppler and possibly CW 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

fluid

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

flow

to move in a stream; volume flow rate

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 levels slide over each other in a smooth, orderly manner, with no mixing between layers

luminance

brightness of 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 velocity

Poiseuille equation

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 info is shown on a display

pulsatile flow

flow that accelerate 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 freq in a Doppler signal for display as a Doppler spectrum.

spectral broadening

the widening of the Doppler shift spectrum

spectral Doppler display

the presentation of Doppler info in a quantitative form of Doppler shift verses time

spectrum analyzer

a device that derives a freq 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, multi-directional flow of a fluid with mixing between layers, flow that is not laminar

variance

square of standard deviation one of outputs of the auto-correlation process.

viscosity

resistance of a fluid to flow

volumetric flow rate

volume of fluid passing a point per unit of time

wall filter

an electric filter that passes freq above a set level and eliminates strong, low freq 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