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.
