Ch. 5 wkst 3 - 6 Flashcards
Doppler effect
a change in frequency caused by the motion of reflectors.
Doppler shift
reflected frequency minus incident frequency; a change in frequency that occurs as a result of motion.
fD(kHz)-fR-fT OR
DopplerShift = [2 x v of blood x freq of transducer x cosΘ] / propagation speed
Doppler angle
the angle between the sound beam and the flow direction.
Spectral analysis
separation of frequencies in a Doppler signal for display as a Doppler spectrum.
Aliasing
improper Doppler-shift information from a pulsed-wave Doppler or color Doppler instrument when the true Doppler shift exceeds one half the PRF.
Nyquist limit
the Doppler-shift frequency above which aliasing occurs. (PRF/2) MHz
Color Doppler display
the presentation of two-dimensional, real-time Doppler-shift information superimposed on a real-time, gray-scale, anatomical, cross-sectional image.
Autocorrelation
a rapid technique, used in most color Doppler instruments, for obtaining mean Doppler-shift frequency.
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.
Clutter
noise in the Doppler signal that generally is caused by high-amplitude, Doppler-shifted echoes from the heart and vessel walls.
Priority
the gray-scale strength below which color Doppler information is shown preferentially on a display.
Baseline shift
movement of the zero Doppler-shift frequency or zero flow speed line up or down on a spectral display.
Ensemble length
number of pulses used to generate one color Doppler image scan line.
Variance
a measure of spectral broadening.
Power Doppler Display
color Doppler display in which colors are assigned according to the strength (amplitude, power, intensity, energy) of the Doppler-shifted echoes.
Hue
the color perceived based on the frequency of light.
Saturation
the amount of hue present in a mix of white.
Luminance
brightness of a presented hue and saturation.
Power Doppler Display
color Doppler display in which colors are assigned according to the strength (amplitude, power, intensity, energy) of the Doppler-shifted echoes.
Continuous Wave
a wave in which cycles repeat indefinitely; not pulsed.
CW Doppler
a Doppler device or procedure that uses CW ultrasound.
Bidirectional Instrument
is an instrument that is capable of distinguishing between positive and negative Doppler shifts (forward and reversed flow).
Sample Volume
the anatomical region from which pulsed Doppler echoes are accepted.
