Kremkau Chapter 5 key terms Flashcards
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 presentation of 2D, real time Doppler shift information in color superimposed on real time, gray scale, anatomic, cross sectional image.
compliance
distensibility; nonrigid stretchibility 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
disturbed flow
flow that cannot be described by straight, parallel streamlines.
Doppler angle
the angle between the sound beam and 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 or 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 a 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 to pass
hue
the color perceived base 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 with 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 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 or standard deviation; one of the outputs of the autocorrelation process; a measure of spectral broadening.
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 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.
