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Physics 1 > C7: Doppler > Flashcards

C7: Doppler Flashcards

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1
Q

define doppler effect

A

a perceived change in pitch due motion of the source of sound or the observer

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2
Q

when a source of sound is moving towards you, will the pitch be higher or lower

A

higher

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3
Q

when a source of sound is moving away from you, will the pitch be higher or lower

A

lower

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4
Q

what 3 pieces of information can spectral doppler tell you

A

presence of flow
direction of flow
quality of flow

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5
Q

when you are using duplex scanning, how many pulses does the machine send out

A

2….. 1 for 2D image and 1 for spectral doppler

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6
Q

the amount of doppler shift depends on what 2 qualities of blood flow

A

direction and velocity of RBCs

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7
Q

is the intensity of Rayleigh scatter proportional to the # of RBCs passing through the SV

A

yes (so it indicates the quantity of blood in a sample)

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8
Q

the doppler shift is based on what principle

A

wave interference

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9
Q

what causes a beat frequency

A

when the reflected sound wave varies slightly in frequency from the transmitted frequency

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10
Q

what is the most basic doppler formula

A

Doppler shift = received frequency - transmitted frequency

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11
Q

describe fast Fourier transformation

A

mathematical technique that separates individual doppler shifts from the beat frequency and displays them in a spectral waveform

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12
Q

what is the detailed doppler formula

A

Change in frequency = (2 (operating F) x velocity x cos theda) / c

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13
Q

as the angle of insonation increases, what happens to the doppler shift

A

it gets smaller

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14
Q

is a lower or higher frequency probe better for doppler and why

A

lower

lower is better because the RBCs return weak echos (they attenuate a lot)

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15
Q

when using duplex scanning, how will the frequencies used diff b/w the 2D image and the doppler signal

A

2D: higher frequency for better resolution

doppler: lower to reduce attenuation

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16
Q

why is the angle of insonation so important for doppler

A

it effects the velocity reading so will make calculations incorrect if its inaccurate (greater than 60)… and the angle increases so does the % error for velocity

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17
Q

whats the most accurate angle for doppler

A

zero

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18
Q

what is the nyquist limit

what happens if its exceeded

A

the limit reached when the RBC velocities are faster than the machines ability to sample

it is equal to 1/2 the PRF… if half the PRF is EXCEEDED than aliasing will occur b/c RBCs arent being sampled fast enough

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19
Q

what is another word for PRF

A

scale or velocity range

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20
Q

what are the 5 ways to correct for aliasing

which are acceptable to use?

A
  1. move the baseline
  2. increase the PRF
  3. increase the doppler angle
  4. lower the operating frequency
  5. change to CW

1 and 2

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21
Q

where should the SV be placed in a vessel for doppler

A

in the middle of the vessel or at the area of highest velocity

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22
Q

what is multi-gating

A

allows you to sample multiple depths at the same time

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23
Q

what are the 3 things that determine the SV

A

beam width
gate length
length of the emitted pulse (e.g. # of cycle in a pulse)

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24
Q

true of false…. the SV is equal to 1/2 the pulse length + the gate length

A

true

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25
Q

for doppler, are longer or shorter pulse better

why?

A

longer pulses…. it results in a more accurate beat frequency/doppler shift

26
Q

minimum number of cycles-per-pulse required for spectral doppler

A

4 cycles per pulse

27
Q

is range gating possible w/ CW?

what about angle correct?

A

no

no

28
Q

where is the CW doppler SV found? what is it called

A

at the intersection of the transmitted and received beam… called the zone of sensitivity

29
Q

with CW, how do we compensate for the fact that angle correct is not possible

A

you must get parallel to flow

30
Q

does CW have a nyquist limit

can you get aliasing?

A

no b/c youre always sampling

no

31
Q

do you have an image w/ CW

A

no

32
Q

whats the problem with the large SV that CW has

A

theres the possibility of picking up the waveform of more than 1 vessel

33
Q

what does the doppler spectral tracing represent

A

the range of doppler shift frequencies produced from each RBC that passed through the SV

34
Q

what are the 3 axes shown in a doppler spectral tracing

A

time (x)
frequency or velocity (y) - can be either
power (z)

35
Q

how is the z axis/power represented in a spectral tracing

what does it depend on

A

represented by the brightness of pixels

it is proportional to the number of RBCs moving at one specific velocity at a given time

36
Q

what does a bright spectral tracing indicate

A

theres a large number of RBCs moving through the SV at that velocity

37
Q

what are the 5 parts of a spectral wave form?

A
  1. peak systolic velocity
  2. envelope (thickness of the tracing, showing range of velocities)
  3. window (area under the tracing)
  4. dicrotic notch
  5. end diastolic velocity
38
Q

which small blood vessels help determine the shape of the spectral tracing

A

arterioles

39
Q

is the y axis of the spectral tracing usually expressed as frequency or velocity

A

velocity

40
Q

why is velocity preferred over frequency for the y axis

A

it compensates for variation is vessel alignment and its more meaningful to the technologist

41
Q

do pulsatility and resistance mean the same thing

A

yes

42
Q

what are the characteristics of high pulsatility/resitance waveforms

A
  • tall, narrow, sharp systolic peak

- reversal or absent diastolic flow

43
Q

in which vessels do we commonly see high resistance waveforms?

A

arteries of the extremities…. body parts that are not vital to life

e.g. CFA

44
Q

what are the characteristics of low pulsatility/resistance waveforms

A
  • broad systolic peak

- forward flow through diastole

45
Q

in which vessels do we commonly see low resistance waveforms?

A

in vessels that feed vital organs

e.g. ICA, renal arteries

46
Q

are low resistance waveforms typical removed from the baseline?

A

yes, b/c there is always constant forward flow

47
Q

what are the characteristics of moderate pulsatility/resistance waveforms

A
  • tall, narrow, sharp systolic peaks

- forward flow through diastole

48
Q

in which vessels do we commonly see moderate resistance waveforms?

A

vessels that feed both high and low resistance vascular beds

e.g. CCA (splits into ICA and ECA)

49
Q

what is the pulsatility index

what is the formula

A

formula used to quantify the impedance to flow (like in the case of a stenosis)

PI = A - B / Mean

A = peak systolic velocity
B = furthest point from peak systole
50
Q

what is the resistive index

what is the formula

A

formula used to evaluate the resistance to flow (like in the case of a transplanted organ)

RI = A - B / A

A = peak systolic velocity
B = endiastolic velocity
51
Q

what is the systolic/diastolic ratio

what is the formula

A

formula to quantify the change in pulsatility

S/D ratio = A / B

52
Q

what does it say about the resistance of a vessel if the S/D ratio is low?
high?

A

the vessel is low resistance

the vessel is high resistance

53
Q

formula for acceleration

A

A = delta V / delta T

54
Q

what is spectral broadening

what does it indicate

A

the vertical thickening of the spectral tracing or envelope

indicates that there is a greater range of velocities w/in the SV

55
Q

if the velocities of the RBC are all the same, how will the spectral tracing appear

A

thin

56
Q

what can cause spectral broadening

A

disturbances in flow: bifurcations, anastomoses, curves in vessels

pathology in arteries = plaque

57
Q

what is false spectral broadening

why does it occur

A

an artifact that can occur when doppler gains are too high or if the SV gate length is too large relative to the vessels

58
Q

what is autocorrelation

A

mathematical technique that assess the doppler shift signal to determine the mean, luminance and variance

59
Q

what is the rouleau effect

A

when RBCs clump together, common in low flow vessels.

looks like smoke on the US monitor

60
Q

what is the purpose of the zero crossing detector

A

it counts how many times the voltage shifts from + to – …. more shifts means higher frequency and greater doppler shift

Physics 1 (7 decks)

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