Doppler Principles Flashcards
a change in pitch results from the relative motion of the source of the sound or the receiver
doppler effect
what is the Doppler effect
a change in pitch results from the relative motion of the source of the sound or the receiver
when the sound source is moving towards the wave, crest are ______ and the pitch is _____, or if moving away from you, the crests are _____ and the pitch sounds ____
closer together
higher
further apart
lower
doppler information is orimarily used to assess ____ both _____ and _______
blood flow
qualitatively
quantitatively
doppler can give you the following info (3)
presence of flow
direction of flow
quality of flow
doppler information is provided by (3)
spectral tracing
colour image
audible sound
duplex scanning
when scanning both the 2D image and doppler simultaneously (shows image and spectral tracing at same time)
triplex scanning
scanning 2D image, doppler, and colour doppler
RBC diameter and what it means
7 um
smaller than typical wavelength = Rayleigh scatter
doppler shift is based on the principle of ____ and doppler shift formula
wave interference (reflected wave varies slightly in f from transmitted wave = beat frequency)
doppler shift = received f - transmitted f
basic doppler formula
more detailed doppler formula
formula that means most to us as sonographers
- doppler shift = received f - transmitted f
- Δf= (2fo x v x cos0) /c
2fo = operating f
v = velocity of RBC
cos0 = angle to vessel
- v = (Δf x c) / (2fo x cos0)
as the operating f increases, the doppler shift ____ (_____ relationship)
increases
linear
since RBCs return very little intensity, a ____ f probe is needed for doppler
lower
as RBCs move faster, the difference in the returned f _____, therefore _____ the doppler shift (_____ relationship)
increases
increasing
linear
cosine 90 = ____ so if the beam is perpendicular to vessels, doppler shift ____ be calculated
0
cant
the angle of insonation impacts the ___ calculated (angle up = doppler ____)
velocity
down (due to cosine of angle)
as the angle of insonation increases, the percent error for velocity ____
increases
Nyquist limit
the limit is reached when the RBC velocities are faster than the machine’s ability to sample
(pulses can only be sent out as fast as they can be returned and are limited by the speed of sound in soft tissue)
the Nyquist limit is equal to ____ the PRF
1/2
if the PRF is greater than 1/2 (Nyquist limit exceeded) , ____ occurs
aliasing
1/2 PRF usually falls between _____ kHz
5-30
why does aliasing occur
the RBC are not being sampled fast enough so a false reading occurs and parts of the signal are wrapped around the baseline
how can the Nyquist limit help with a diagnosis
plaque in lumen increasing velocity = exceeds Nyquist limit = aliasing
how to know if it is aliasing rather than reversal
if showing both extreme colours and no zero velocities (black) = aliasing, not reversal
correcting for aliasing can be accomplished by (5)
increase the PRF
move the baseline
increase the Doppler angle (heel or toe of the probe)
lower the operating frequency
change to continuous wave
what two ways to correct aliasing are used most often and which one first
increase PRF (1st) (AKA scale/ velocity range)
move the baseline (decrease to add room on top)
since pulsed sound is used to doppler it ___ possible to define a sample volume or gate
is
the sample volume is created because of the ____
range equation
sample volume determined by (3)
the beam width (depends on depth/focus)
the receiver gate length
the length of the emitted pulse (short=less data)
the ____ the pulse duration the more accurate the beat frequency
longer
a minimum of __ cycles/pulse is required for doppler (opposite to what)
4
opposite to 2D scanning where short PD is best
range gating ____ possible with continuous wave doppler
not
zone of sensitivity
area of intersection between the received beam and transmitted beam where CW Doppler sample volume is found
how big is the zone of sensitivity and what does this mean
5-6cm
large sample volume= chance for picking up more than one vessel = very complex spectral tracing
the spectral tracing of doppler frequencies generated by moving blood that we see is plotted along the following axes (3)
time (x)
frequency or velocity (y)
power (z) (brightness of the pixels)
what is power in spectral tracing proportionate to
the number of blood cells moving at one velocity at given time (brighter=more RBCs in a sample)
five parts of a spectral analysis (and be able to draw/label it)
peak systolic velocity
envelope
window
dicrotic notch
end diastolic velocity
the way in which the system creates a spectral trace is through a process called
Fast Fourier Transform (FFT)
mathematical technique seperating individual Doppler shifts from the complex beat frequency
Fast Fourier Transform (FFT)
the process in which the system creates a spectral trace
y axis of spectral analysis represented by
either the frequency of the Doppler shift or the velocity of the RBCs
frequency on a spectral analysis is expressed in and velocity too
kHz or Hz
cm/s or m/s
antegrade vs retrograde (and what it is expressed by on y-axis)
towards to probe (pos number)
away from the probe (neg number)
blood can be categorized as ____, _____, or ____
high
moderate
low pulsatility
how else can the pusitility of blood be referred as
resistance (high, mod, low)
what is the determining factor to blood pulsitility
what it is supplying (brain=low pulsitility/resistance, limbs=high)
high pulsatile/resistance blood on spectral analysis has (2) (where its common)
tall, narrow systolic peaks
reversed or absent diastolic flow
common in extremities (CFA)
low pulsatile/resistance blood on spectral analysis has (2) (where its common)
broad systolic peaks (rapid upstroke, comes down slower)
forward flow through diastole (doesn’t reverse/cross baseline)
feeding vital organs (ICA)
moderate pulsatile/resistance blood on spectral analysis has (2) (where its common)
tall, narrow, sharp systolic peaks (high)
forward through through diastole (low) (sometimes little reversal in late systole)
feed both high/low resistance vascular beds depending on the physiological state (CCA)
4 qualitative assessments of a waveform
presence of flow
direction of flow
laminar or turbulent
spectral broadening (thick envelope)
5 quantitative assessments of a waveform
pulsatility index
resistive index
doppler shift
peak velocity
mean velocity
pulsatility index is used to _______ and its formula
quantify the impedance to flow like in the presence of a stenosis
PI = (A-B)/mean velocity
A=PSV
B= furthest away velocity
the systolic/diastolic ratio is another means of quantifying a ____ and its formula
change in pulsatility
S/D ratio= A/B
A= PSV
B=EDV
when S/D ratio increases, resistance ____
increases
acceleration formula
Acceleration = Δv / ΔT
V=PSV
T= time from start to PSV
spectral broadening
the vertical thickening of the spectral trace or envelope
all v at same time=thin line
greater range of v=spectral broadening
false spectral broadening
artifact that occurs when Doppler gain is set too high or sample volume gate is large relative to the vessel
A mathematical technique that rapidly asses the Doppler shift signal to determine the mean, luminance and variance
AUTOCORRELATION
A colour coding technique that employs the amplitude of the Doppler shifts thus being less angle dependant and more sensitive to low flow states
power doppler
The area of interest for pulsed wave spectral Doppler comprised of the beam width, the receiver gate and the emitted pulse
sample volume
This occurs when the second scan line is sent out before the first one has returned. It is a possibility when performing Doppler in a high PRF mode
range ambiguity
The continuous wave region of interest for spectral Doppler where the transmitted and received beam intersect
zone of sensitivity
