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Physics > Module 7 : Doppler Principles > Flashcards

Module 7 : Doppler Principles Flashcards

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1
Q

what is a doppler shift

A
  • a change in pitch results form a relative motion of the source of the sound or the reciever
  • when a sound source is moving towards you the wave crests are closer together and pitch is higher or moving away from you the crests are further apart and pitch is lower
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2
Q

what 3 things does doppler give us information on

A
  • presence of flow
  • direction of flow
  • quality of flow
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3
Q

what are three different types of doppler

A
  • spectral trace
  • color image
  • audible sound
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4
Q

how is the Doppler effect produced with blood

A
  • sound reflects of moving RBCs which alter the frequency that is returned
  • the amount of change is related to the direction and speed of the RBCs
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5
Q

what does the intensity of the signal relate to

A
  • proportional to the number of RBCs and thus indicates the quantity of blood in the sample
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6
Q

what is the doppler shift equation

A
  • doppler shift = received - transmitted
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7
Q

how is the doppler shift determined

A
  • uses the beat frequency

- reflected wave differs from transmitted frequency

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8
Q

what is the more detailed doppler shift equation

A

^F = 2Fo x v x cos0 / c

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9
Q

does doppler use a higher or lower frequency

A
  • lower frequency

- RBCs very small so already reflect very little of the echoes

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10
Q

what is the most accurate angle of insonation for doppler

A
  • most accurate would be 0º

- we use 60º accurate and reproducible

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11
Q

what is the nyquist limit

A
  • reached when RBC velocity faster than machines ability to sample
  • pulses only sent out as fast as they can be returned and are limited by the speed of sound in tissue
  • causes aliasing
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12
Q

what is the nyquist limit equation thing

A

1/2 PRF

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13
Q

what is aliasing

A
  • wrapping of the color or the spectral trace around the baseline
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14
Q

what are the five ways we can correct for aliasing

A
  • move the baseline
  • increase the PRF
  • increase doppler angle
  • lower the operating frequeny
  • change to continuous wave
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15
Q

what two methods o correct for aliasing do we use in practice

A
  • move baseline

- increase PRF

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16
Q

where should the sample volume be placed in the vessel

A
  • middle of vessel

- where the highest velocity is

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17
Q

what are the 3 components of the sample volume

A
  • beam width (3D)
  • receiver gate length
  • length of emitted pulse
18
Q

what decreases the gate length

A
  • pulse length reduced

- improve spectral display

19
Q

do you want long or short pulse for doppler

A
  • long pulses to interact with the RBCs longer
20
Q

instead of range gating what is used with continuous wave doppler

A
  • no image so uses zone of sensitivity
21
Q

what is the zone of sensitivity

A
  • intersection of transmitted and received beam
22
Q

what is the spectrum

A
  • array of components of a wave arranged in order of increasing frequency over time
23
Q

what are the three components of the spectral trace

A
  • time (x)
  • frequency or velocity (y)
  • power (z)
24
Q

what is the power (Z axis) of the spectral trace

A
  • represented by brightness of the pixels

- proportionate to the number fo blood cells moving at one velocity at a given time

25
Q

what is the way in which a system creates a spectral trace

A
  • fast Fourier transform
26
Q

what is the Y axis of the spectral trace

A
  • represent either frequency of the doppler shift or velocity
  • velocity is preferred
27
Q

what is the flow direction of RBCs relative to

A
  • the transducer
28
Q

what does antegrate flow mean

A
  • towards the probe expressed as positive number
29
Q

what is retrograde flow

A
  • flow away from the transducer expressed as a negative number
30
Q

what are the 3 different categories of pulsatility

A
  • high
  • moderate
  • low
31
Q

what are the characteristics of high pulsatility or high resistance flow

A
  • tall narrow sharp systolic peak

- reversed or absent diastolic flow

32
Q

where is high resistance flow seen in body

A
  • arteries of the extremities
33
Q

what are the characteristics of low pulsatility or low resistance flow

A
  • broad systolic peaks

- forward flow through diastole

34
Q

where do we see low resistance flow

A
  • vessels that feed the vital organs
35
Q

characteristics of moderate pulsatile or moderate resistance flow

A
  • tall narrow sharp systolic peak

- forward flow through diastole

36
Q

what is the pulsatility index equation

A
  • PI = A (peak velocity) - B (lowest velocity) / mean
37
Q

what is the resistivity index equation

A
  • RI = A - B / A
38
Q

what is the systolic diastolic ratio

A

S/D = A/B

39
Q

acceleration equation

A

acceleration = ^v / ^t

40
Q

what is spectral broadening

A
  • vertical thickening of the spectral trace or envelope
41
Q

what is false spectral broadening

A
  • artifact that occurs when doppler gain is set too high

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