Doppler Flashcards
change in frequency of a sound wave due to motion between source of sound and its receiver
doppler effect
difference between the transmitted and received frequencies
doppler shift
received > transmitted
positive
transmitted > received
negative
relationship between blood cell velocity and Doppler shift
direct
Doppler shift equation
reflected f - transmitted f
Doppler shift is within audible range of
20-20kHz
the process of extracting the doppler shift
demodulation
blood moving toward transducer elicits a
positive doppler shift
blood moving away from the transducer elicits a
negative doppler shift
true velocity x cosine of beam angle = ?
measured velocity
what does true velocity depend on
cosine of beam angle and direction of flow
distance RBC travels divided by speed
speed
defines magnitude and direction of travel
velocity
what does the 2 stand for in the doppler equation
double Doppler shift (one is transmitted, one is received)
relationship between Doppler shift and transducer frequency
direct
relationship between Doppler shift and speed
inverse
is there a Doppler shift when RBC aren’t moving?
no
a doppler that senses Doppler shift but does not provide any information about direction
nondirectional doppler
what does non-coherent mean
can’t tell if sound beam is coming toward or away from us
bidirectional doppler can distinguish between ___
positive and negative doppler shifts
technique used to process bidirectional doppler
phased quadrature
what do you called phased quadrature that detects alias
quadrature detection
of crystals in CW doppler
2
duty factor in CW
1 or 100%
is CW an imaging trx?
no
advantage of CW doppler
sensitive to high velocities
disadvantages of CW doppler
range ambiguity /
deep reflectors have a low amplitude and may falsely represent fewer reflectors
duplex imaging
2D and doppler
dedicated CW / PEDOF
2 semicircular crystals with no backing material undampened signal narrow bandwidth high Q factor high sensitivity
Doppler shift is the ___ of two frequencies
difference
if the frequency of a sound wave changes when there is motion between the sound source and receiver, what other parameters change
wavelength and period
what’s the problem with continuous wave doppler
range ambiguity
can you elicit a Doppler shift with a non directional doppler?
yes
number of crystals in PW
1
does PW have range ambiguity or range resolution
range resolution
what does sample volume calculate
time of flight
what does range resolution mean
you can choose the location for sample volume
PW is used to
create images
do PW doppler try have backing material?
yes
is Q factor high or low in PW
low
is bandwidth wide or narrow in PW
wide
is PW highly sensitive?
no
imaging at ___ degrees creates optimal images in PW
90
imaging at __ degrees is best for velocity measurements in PW
0
disadvantages of PW
aliasing
defines when aliasing will occur
nyquist limit
when will aliasing occur
when the f>half the PRF
as PRF goes down, likelihood to alias ___
increases
low sampling rate creates _______ display
erroneous
increased sample volume depth = _____ nyquist limit
lower
sampling rate is the same thing as…
PRF
shallow sample volume = ___ PRF
high
with deep sample volume, aliasing is (more/less) likely
more
relationship between doppler f and transducer f
direct
are low f trx more or less likely to alias
less
how to avoid aliasing
adjust scale adjust baseline use low f trx obtain image at lowest depth use CW
gray shades of a spectrum are related to:
amplitude of reflected signal / # of RBC creating the reflection
Doppler shift produces info about…
blood flow velocity
units of Doppler effect
change in frequency in Hz
which doppler has a high Q factor
CW
relationship between depth and PRF
inverse
fast moving blood is ___ likely to alias
more
why do we need perpendicular incidence in color doppler
we need an angle other than 90 to see color
if we see grayscale noise in spectral doppler, the gain is
too high
when too much aliasing occurs in color doppler, adjust the ___
scale
when the door scale is TOO high, what happens to the color
we lose important color (removes low flow)
what does wall filter eliminate
low f doppler shifts
fixes “ghosting”
reduces ‘clutter’
broad range of colors indicates
turbulent flow
if doppler is too bright, adjust the
gain
color map with only red and blue shown
velocity map
what does it mean when a color doppler turns black
no flow / 90 degrees
bright red and yellow doppler indicates what type of doppler
power doppler
another name for spectral doppler mirror
crosstalk
how is color doppler processed
autocorrelator
how is spectral doppler processed
FFT
does color doppler have range resolution?
yes
relationship between color doppler packet size and frame rate? accuracy?
inverse, direct
turbulent flow is shown on what side of a variance map
right side
does power doppler alias?
no
