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Vascular > Module 3 : Doppler Principles > Flashcards

Module 3 : Doppler Principles Flashcards

1
Q

doppler principle

A

change in frequency of sound, light, or other waves caused by the motion of the source or the observer

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2
Q

Doppler effect - ultrasound

A
  • change in frequency of sound caused by the motion of red blood cell (relative to transducer)
  • difference between transmitted frequency (transducer frequency) and received frequency (reflected or echo frequency)
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3
Q

movement toward transducer

A
  • echo frequency larger than transducer frequency

- ANTEGRADE FLOW

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4
Q

movement away transducer

A
  • echo frequency will be smaller than transducer frequency

- RETROGRADE FLOW

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5
Q

methods used to detect and analyze doppler shifts

A
  • color flow
  • spectral waveforms
  • audible sounds
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6
Q

doppler shift basic equation

A

Fd = Fr - Fo

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7
Q

doppler shift dependent factors

A
  • transmitted (sent) frequency
  • velocity of the moving blood
  • angle between the moving blood and the sound beam
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8
Q

complex doppler shift equation

A

Fd = 2 x Fo x V x cos0 / c

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9
Q

angle of insonation

A
  • MOST IMPORTANT FACTOR that influences calculation of the DOPPLER SHIFT
  • ideal orientation would be at an angle 0 (largest doppler shift) cos 0 = 1 THIS IS VIRTUALLY IMPOSSIBLE TO ATTAIN EXCEPT IN HEART
  • when the blood flow is at an angle of 90 (cos 0 = 0) there is NO SHIFT DETECTED so NO MEASURABLE RETURNING FREQUENCY
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10
Q

correct doppler angle

A

30 - 60 to the blood vessel

- REDUCE MARGIN OF ERROR, REPRODUCIBLE

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11
Q

doppler angle greater than 60

A
  • doppler shifts difficult to quantify due to large margin of error
  • lead to errors in estimates of peak frequency
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12
Q

venous flow assessment

A
  • angle is not important
  • velocities are not used
  • angle correct is set to zero
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13
Q

continuous wave doppler (CW)

A
  • continuously excited
  • contains two piezoelectric elements
    + one transmitting, one receiving
  • no image produced
  • impossible to select a specific depth and region to sample
  • knowledge of the anatomy
  • advantage : sample high velocity with no aliasing
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14
Q

pulsed wave doppler

A
  • sound pulses produced by the transducer at regular intervals
  • isolate signals from a desired depth
  • PRF limits measurement of high velocities by producing aliasing
  • pulsed doppler instruments combined with real time B Mode
  • B mode allows visualization of structure
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15
Q

nyquist limit

A
  • doppler shift exceeds 1/2 the PRF

- occurs when insufficient amount of time to collect the returning signal information before next pulse is sent

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16
Q

spectral display

A
  • doppler shift frequencies are separated into individual frequency components using FAST FOURIER TRANSFORM
  • displayed as a spectrum or “image” of the doppler frequency
    + time = horizontal axis (x)
    + velocity = vertical axis (y)
    + brightness of pixel - the z axis ( proportional to the # of rbc’s)
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17
Q

Quadrate detection

A
  • processes the signal as a (+) or (-) value depending on direction of flow relative to the doppler beam
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18
Q

peak systole

A
  • peak velocity of the cardiac cycle
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19
Q

dicrotic notch

A
  • early diastole flow reversal signifies closing of the aortic valve
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20
Q

end diastole

A
  • velocity at end diastole just prior to systole
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21
Q

envelope

A
  • white line that outlines the changes in frequencies

- determined by the number of blood cells in a sample

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22
Q

window

A
  • Clear area below the envelope that displays no frequencies
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23
Q

spectral broadening

A
  • ” thickness” of the white line up to “filing in” of window
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24
Q

Pulsatility

A
  • relationship of peak minimum velocities over the mean velocity of an entire cycle
  • can be low, moderate, and high
25
Q

resistivity

A
  • relationship of peak systolic velocity to end diastolic velocity
  • low or high resistance waveforms
26
Q

low resistivity

A
  • has diastolic flow above zero

- organs that need flow constantly have low resistance wave forms

27
Q
  • high resistance
A
  • usually shows reversed flow in early diastole
28
Q

laminar flow

A
  • MOST COMMON
  • all blood particles move forward
  • blood moves in concentric layers
  • highest velocities at the centre and crease in speed as you move toward the wall
  • AVERAGE VELOCITY IS 1/2 THE MAX VELOCITY
  • stationary layer against vessel wall
  • parabolic, plug, blunt
29
Q

factors affecting flow

A
  • velocity
  • change in diameter
  • curves, bifurcation, branch origins
30
Q

disturbed pattern

A
  • friction and energy loss disrupt laminar flow
  • still forward flow but with diverging direction
  • mild version of turbulence but still considered normal
31
Q

turbulent

A
  • non linear flow
  • multiple directions
  • multiple velocities
  • considered abnormal
32
Q

spectral optimization

A
  • gain, baseline, wall filter, scale/prf/velocity range,
33
Q

gain - spectral

A
  • adjust to allow visualization of signal without unwanted noise
  • too high of gain will create false spectral broadening or unwanted noise artifacts
34
Q

baseline

A
  • adjust to allow entire spectral signal to be seen

- too high of baseline may cause aliasing

35
Q

wall filter

A
  • eliminates low frequency noise

- adjust to ensure low velocities not missed

36
Q

scale, prf, velocity range

A
  • adjust to demonstrate peak and minimum velocities
  • too low of prf will cause aliasing
  • increase prf to correct aliasing
37
Q

power doppler

A
  • power or intensity measured instead of direction
  • based on density of RBC not speed
  • no ailiasing
  • more sensitive and no doppler angle
  • asses small vessels with little flow
  • less subject to blooming
  • ## slow frame rate
38
Q

color doppler

A
  • stationary reflectors make up gray scale portion
  • interference with moving RBCs create doppler shift
  • represents mean frequency
  • doppler shifts are cooler coded corresponding to direction and velocity
  • hundreds of sample lines
  • autocorrelation
  • qualitative not quantitative
  • reduces prf
  • fram rate decrease
39
Q

color flow display

A
  • map

- optimization of color

40
Q

maps

A
  • bar or wheel
  • various color maps
  • SHIFTING HUE MOST COMMON (diff colours diff frequency)
  • CHANGING SHADE (saturation) same color but different shade
  • VARIANCE MAPS tag certain frequencies
41
Q

optimization of color

A
  • velocity range
  • doppler angle
  • field of view
  • color box size
  • color scale
  • gain
  • color priority
  • wall filter
  • baseline
  • maps
  • power
  • invert
42
Q

velocity range- color

A
  • high flow / high prf and low flow/ low prf
43
Q

doppler angle

A
  • steer probe and or color box
44
Q

field of view

A
  • greater depth to area of interest degrades image and ability to display flow
45
Q

color box size

A
  • smaller is better , height has no effect on frame rate

- width decrease frame rate

46
Q

color scale prf

A
  • to low prf result in aliasing

- to high prf no flow detected or vessel not filled in

47
Q

gain - color

A
  • insufficient gain result in poor color fill in

- increase till bleeding then go back to threshold

48
Q

color priority

A
  • image processing priority tray scale vs color
49
Q

wall filter - color

A
  • high setting may eliminate low flow info
50
Q

baseline - color

A
  • adjusted from middle of scale to accommodate more red or blue velocities
51
Q

maps - color

A
  • ise map to help assess flow
52
Q

power / angio

A
  • in case of trickle or low flow
53
Q

invert

A
  • observe orientation of vessel to transducer
54
Q

color artifactis

A
  • mirror image
  • blooming
  • color flash
  • aliasing
  • visible bruit
55
Q

mirror image artifact

A
  • seen in gray scale, color and spectral

- mirror of real vessel

56
Q

blooming/ bleeding

A
  • due to high gain setting may obscure pathology
57
Q

color flash

A
  • transmitted pulsations or adjacent motion will cause color to flash outside of vessel
58
Q

aliasing

A
  • inappropriate prf setting may cause color to exceed high velocity threshold
59
Q

visible bruit

A
  • soft tissue vibration adjacent to area of high flow

Vascular (7 decks)

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