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