Doppler Flashcards
what is the doppler effect?
the change in frequency or wavelength of echo signals that occurs when there is relative motion between the transducer (sound source) and reflecting surfaces (red blood cells)
flow toward the transducer is?
a positive doppler shift
flow away from the transducer is?
a negative doppler shift
what is the difference between the recieved and transmitted frequencies?
the doppler shift
what units are used to express doppler shift?
kilohertz or kHZ
the frequency transmittes by the transducer can also be referred to as?
transmitted frequency
emitted frequency
incident frequency
operating frequency
transmitted frequency and the change in frequency are inverslely related
true/false
false
they are directly related
ex: if the transmitted frequency is doubled, then the change in frequency is doubled.
where is the cosine of the angle measured?
between the direction of blood flow and the axis of the beam.
what are the cosines for the following angles?
0°
60°
90°
1
.5
0
what factors influence the magnitude of the doppler shift frequency?
range of the doppler shift frequencies
effects of beam angle
transmitted frequency
if the RBC’s are moving toward the transducer, what waveforms are displayed?
a positive doppler shift
if RBC’s are moving away from the transducer, what waveforms are displayed?
a negative doppler shift
if you have a faster flow velocity, you will have a higher doppler shift.
true/fasle
true
how many crystals does a CW probe use?
2
one sends & one receives
what are the advantages for CW?
ability to measure high velocities
no aliasing
small probe sizes
ability to use high frequencies
what is the biggest disadvantage for CW?
range ambiguity; inability to determine where the doppler signal is coming from
how many crystals are used for PW?
1
the term applied when only the information from the selected gate will be processed is?
range resolution
what is the nyquist limit? what is the formula?
the level at which aliasing will begin to occur
1/2PRF
aliasing occurs as the bottom of the spectrum wrapping around into the opposite half of the baseline
true/false
false
it is the top of the spectrum
what are ways to correct aliasing?
- properly adjusting the spectral baseline &/or spectral scale
- try a different window that gives a shallower depth
- using a lower frequency transducer
what is an advantage of PW doppler?
range resolution
in spectral analysis, what is displayed on the horizontal axis?
time
in spectral analysis, what is displayed on the vertical axis?
frequency shift or velocity
a poitive doppler shift is below the baseline?
true/false
false; it is above the baseline.
wave form brightness is also known as what?
the amplitude of the signal
what does FFT stand for?
fast fourier transformer
what is FFT?
a device that converts the doppler shift info into the visual spectral analysis
FFT breaks down these complex signals into each individual frequency
true/false
true
what is the range of packets per line of color?
3 to 30 pulses
what is the number of pulses sent per line of color refered to as?
packet size or ensemble length
for the color map, the top color is assigned to all velocities flowing in which direction?
toward the transducer
for the color map, the bottom color is assigned to all velocities flowing in which direction?
away from the transducer
faster velocities are represented by darker colors or hues
true/false
false; they are represented by ligher colors
what is saturation?
the degree to which the original color is diluted with white
the deeper the color, i.e. deep red or blue, represent faster flow
true/false
false; faster colors are represented by lighter hues
color doppler is angle dependent
true/false
true
what is triplex imaging consist of?
b-mode
color doppler
pulse wave doppler
what is the disadvantage of color doppler?
aliasing
where in a vessel are you likely to see aliasing?
after stenosis
what is autocorrelation?
a technique used to rapidly obtain doppler shift frequencies used in color flow doppler
autocorrelation has a decreased frame rate, which decreases which resolution?
temporal
power doppler is angle dependent
true/false
false; power doppler is not angle dependent
the most inaccurate doppler shift occurs when the angle is
90°
as the angle between the transducer and flow decreses, the doppler shift:
increases
noise in the doppler signal that is generally cause by high amplitude, doppler shifted echoes is called:
clutter
the wall filter used in doppler is a type of?
reject control
a faster but less accurate signal process used in color flow doppler is called?
autocorrelation
signal processing of the doppler signal is accomplished by the?
fast fourier transform (FFT)
color power/energy mode is also known as
color angio or power doppler
