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Ultrasound Physics > Doppler > Flashcards

Doppler Flashcards

1
Q

What is Doppler

A

broad category which includes spectral Doppler, waveform Doppler, audio Doppler, color flow imaging

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2
Q

Doppler Effect

A

Shift in frequency

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3
Q

what is Doppler effect used for

A

The mechanism by which blood flow is detected, measured, and monitored noninvasively within the body

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4
Q

how is the doppler effect exemplified?

A

change in pitch that occurs as a high-speed train or car approaches and then speeds past

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5
Q

what is the apparent shift in frequency the result of?

A

changes that occur to the wavelength because of the relative motion

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6
Q

If the object is moving towards the observer

A

The wavelength will be shorter

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7
Q

If the object is moving away from the observer

A

The wavelength will be longer

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8
Q

Therefore, since a shorter wavelength produces a higher frequency

A

The motion towards the observer produces a higher frequency than the original wave

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9
Q

Motion away from the observer

A

Produces a lower frequency than the frequency of eh transmitted wave

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10
Q

Doppler shift is proportional to what

A

The relative velocity

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11
Q

The doppler shift increases as what increases?

A

velocity increases

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12
Q

Doppler shift is also affected by what?

A

Parameters that affect the wavelength

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13
Q

when the distance between the source and the observer is increasing

A

Relative motion is away

Decompression occurs

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14
Q

When the distance between the source and observer is decreasing

A

Relative motion is towards

compression occurs

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15
Q

Compression leads to what?

A

Higher frequency and a positive frequency shift

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16
Q

Decompression

A

Lower frequency and a negative frequency shift

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17
Q

Shift can be what?

A

Positive or negative

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18
Q

A greater shift only tells what?

A

only amount, not direction

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19
Q

Unless we know what, we cannot tell if the shift was positive or negative

A

Must know the relative motion

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20
Q

If the relative motion is towards

A

the greater shift implies an increasing higher frequency

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21
Q

If the relative motion is away

A

greater shift implies an increasing lower frequency

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22
Q

what is the doppler shift

A

Relative difference between the detected frequency and transmitted frequency

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23
Q

when the detected frequency is higher than the transmitted frequency

A

Doppler shift is positive

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24
Q

If the velocity of the train doubles, the frequency shift A) Halves
B) Doubles
C) Cannot be determined because direction is not known

A

B) If the velocity of a train doubles, the frequency shift doubles

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25
Q

If the velocity of the train doubles, the positive frequency shift
A) Halves
B) Doubles
C) Cannot be determined because direction is not known

A

C) Cannot because determined because direction is not known

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26
Q

Which represents a greater Doppler shift, +2kHz or -3 kHz
A) 2 KHz
B) 3kHz
C) cannot be determined

27
Q

As the relative motion increases

A

Doppler Effect also increases

28
Q

wavelength and operating frequency have what kind of relationship

A

Inverse proportional

29
Q

As operating frequency increases

A

Doppler shift also increases

30
Q

As propagation velocity increases

A

Doppler shift decreases

31
Q

Roundtrip effect

A

Measurement is not made by the observer but rather by measuring the reflected frequency back to the transducer

32
Q

As the wave travels to the moving structure

A

there is an associated shift

33
Q

why is there a doubling effect?

A

Structure acts as the source of the reflected wave

The structure is moving as it reflects the wave back to the transducer

34
Q

The doppler shift

A

Can be both positive or negative depending on the direction of motion relative to the observer

35
Q

Simplified Doppler Equation

A

Doppler shift frequency=2transmit frequency velocity of the target through medium/speed of interrogating beam through medium

36
Q

Doppler shift frequency is proportional to

37
Q

Doppler shift frequency is proportional to

A

transmit frequency

38
Q

Doppler shift frequency is inversely proportional to

A

speed of interrogating beam through medium

39
Q

For a given interrogating frequency, if the velocity triples, what happens to the doppler shift frequency?

A

Doppler shift is proportional to the velocity therefore a tripling of the velocity implies a tripling of the Doppler shift

40
Q

If the transmit frequency is changed from 2MHz to 10 MHz, what happens to Doppler shift frequency

A

Doppler shift is proportional to operating frequency an increase in the operating frequency by a factor of 5 implies an increase in the Doppler shift by a factor of 5

41
Q

What is the usual target in diagnostic ultrasound

A

Red blood cells

42
Q

What is the usual observer in diagnostic ultrasound

A

transducer

43
Q

what is the simplified equation for velocity

A

v=c*fdop/2f0

44
Q

The _______ ________ is a shift in frequency caused by relative motion between the observer and target

A

Doppler Effect

45
Q

A positive shift is caused by motion _____________the observer

46
Q

A __________shift is caused by motion away from the observer

47
Q

A Doppler shift will ______if both the target and observer are moving away from each other faster

48
Q

A Doppler shift will _____if both the target and observer are moving towards each other faster

49
Q

The _______the target moves, the higher the Doppler shift

50
Q

The Doppler shift is to the operating frequency

A

Proportional

51
Q

The Dopplere shift is _______to the propagation velocity

A

inversely proportional

52
Q

Because the Doppler effect is based on motion relative to an observer

A

The angle between the observer and the motion affects the Doppler Effect

53
Q

what is the optimal transmit frequency for red blood cells deeper than 3cm?

A

Below 3MHz

54
Q

At shallower depths, high frequencies produce what?

A

Stronger Doppler signals because of increased reflectivity

55
Q

At deeper depths, lower frequencies produce what?

A

Stronger Doppler signals because of the increased absorption that occurs with higher transmit frequencies

56
Q

red blood cells produce what kind of scattering?

A

Rayleigh scattering

57
Q

The amount of scattering increases with….

A

Increased frequency

58
Q

how is Rayleigh scattering related to the frequency

A

Non-linearly

59
Q

What is the problem with increasing frequency

A

Increasing the frequency increases reflectivity but also results in significantly increased attenuation

60
Q

what is spontaneous contrast

A

rouleau formation which allows for the visualization in blood in 2D

61
Q

Spontaneous contrast

A

Can indicate a pathology/hemodynamic problem

62
Q

what is the Doppler Angle

A

The angle that is formed between the observer’s line of sight and the direction of the target object

63
Q

what is the doppler angle also referred to as?

A

Insonification angle or angle of insonification (measured between the beam steering direction and the direction of flow)

64
Q

why is the correct insonification angle important

A
  1. Ability to determine flow direction
    2) Ability to measure doppler measurement accurately
    3) Ability to minimize Doppler Error sources
    4) Ability to assess the likelihood of artifact related issues (spectral broadening)

Ultrasound Physics (10 decks)

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