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Physics > Exam 2 > Flashcards

Exam 2 Flashcards

1
Q

Source (transducer) determines the ______ of the wave

A

Frequency

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2
Q

The medium (RBC’s) determines the ________

A

Propagation speed

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3
Q

Wavelength equation

A

c
—
f

c= propagation speed
f=frequency

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4
Q

Stationary source, transducer =

A

Reference signal

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5
Q

Reflector is moving

A

RBC’s flowing through vessels

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6
Q

Positive Doppler shift the reflector is moving ________ the transducer

A

Toward

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7
Q

Positive Doppler shift the reflected frequency is_________ than the transmitted frequency

A

Higher

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8
Q

Positive Doppler shift
- positive or negative shift?
- above or below baseline?
- higher or lower frequency?

A
  • positive
  • above
  • higher
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9
Q

Negative Doppler shift:
- positive or negative shift
- above or below baseline
- higher or lower frequency

A
  • negative
  • below
  • lower
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10
Q

If reflector is moving away from the transducer the reflected freq is _________ than transmitted freq

A

Lower

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11
Q

Doppler shift equation (frequency)

A

Doppler shift (Hz) = reflected - transmitted

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12
Q

Is the Doppler frequency range within the audible range?

A

Yes, Doppler shift between 200 Hz & 15,000 Hz

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13
Q

Doppler shift equation (velocity)

A

fDOP = 2f0V
——
c

fDOP = Doppler shift
2 = round trip of the sound
f0 = transmitted freq
V = velocity
c = speed of sound in tissue

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14
Q

Doppler frequency is ___________ proportional to the reflector velocity

A

Directly

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15
Q

Reflector velocity doubles = _________ of Doppler frequency

A

Double

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16
Q

Higher transmit frequency = ________ frequency shift
(higher/lower)

A

Higher

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17
Q

Lower transmit frequency = ___________ frequency shift

A

Lower

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18
Q

When distance between source & observer is increasing the relative motion is “away” and a ___________ occurs

A

Decompression

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19
Q

Distance between source & observer decreases, the relative motion is “towards” & a __________ occurs

A

Compression

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20
Q

Compression leads to ________ frequency & a ________ frequency shift
(higher/lower) (positive/negative)

A

Higher
Positive

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21
Q

Decompression leads to a _________ frequency & __________ frequency shift
(higher/lower) (positive/negative)

A

Lower
Negative

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22
Q

Faster velocity will result in a _________(greater or lesser) frequency shift

A

Greater

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23
Q

Doppler equation (angle):

A

fdop = 2foV cos(o)
—————
c

fdop = Doppler shifted frequency
fo = transmit frequency
V = velocity
c = speed of sound through medium
Cos = angle effect
(0) = angle or flow

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24
Q

Where is insonification angle (angle of insonation) measured?

A

Between the beam steering direction and the direction of the flow

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25
Q

When blood cells are moving parallel to a sound beam, how much of the velocity is being measured?

A

Entire velocity is measured

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26
Q

Flow direction toward transducer = (positive or negative) _______ shift

A

Positive

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27
Q

Flow direction away from transducer = (positive or negative) _______ shift

A

Negative

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28
Q

Perpendicular (90 degree) incidence can not be measured. What is the velocity measured?

A

Velocity measured = 0

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29
Q

Angle of incidence must be _____ (≤ ≥) ______ degrees

A

≤
60

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30
Q

Ability to correctly identify the insonification angle is critical for these reasons:

A
  • determine flow direction
  • Doppler measurement accuracy
  • minimize Doppler error sources
  • likelihood of artifact related issues (spectral broadening)
31
Q

What does the Spectral Display, display?

A

The blood flow measurements
- Displaying flow velocities recorded over time (graphically)

32
Q

Spectral display allows for evaluating the following:

A

Blood flow direction - towards or away
Blood flow characteristics - whether flow has high or low resistance & pulsatile and phasic
Quality of flow - turbulent or laminar
Quantification of blood flow - peak or mean velocities

33
Q

What is the difference between the transmit frequency and the received frequency?

A

Doppler shift /effect/frequency

34
Q

Doppler tracing has a “y-axis” representing ________ and “x-axis” representing _________

A

Y - velocity (m/sec)
X - time

35
Q

High resistance flow =

A

Systolic flow

36
Q

Low resistance flow =

A

Diastolic flow

37
Q

Phasic flow is driven by….

A

Respiratory pump

38
Q

Spectral broadening is usually caused by

A

Turbulence

  • results in “fill in” of trace window
  • hallmark feature of post stenotic flow
39
Q

Fast Fourier Transform (FFT) can distinguish _______ flow from _______ flow

A

Laminar
Turbulent

40
Q

Two advantages of FFT

A
  1. Accuracy
  2. Displays individual velocity components that make up the reflected signal
41
Q

Laminar flow travels at _______ and displays _______

A

Similar velocities
Narrow, well-defined tracing

42
Q

Turbulent flow is _______
displays______

A

Chaotic, goes in all directions & velocities

Spectral broadening

43
Q

Sample volume:
Keep cursor ______
Ideal gate size =

A

Center of vessel

1/2 the lumen

44
Q

Range resolution (range ambiguity)

A

Ability to detect signals from a specific area

45
Q

PRP =

A

(1)
—-
PRF

46
Q

PRF is determined by

A
  • Speed of sound
  • Distance it travels
47
Q

What is necessary to measure reflectors moving w/high velocity & producing large Doppler shifts

A

High PRF

48
Q

High PRF allows the pulses to be sent out frequently:

A

Shallow location

49
Q

Low PRF allows the pulses to be sent out less frequently:

A

Deeper location

50
Q

Regurgitant jet velocity is (higher or lower) ________ than the nyquist limit

A

Higher

51
Q

PRF limit where aliasing occurs is called?

A

Nyquist limit

52
Q

Aliasing occurs if the velocity of blood exceeds the? -

A

Nyquist limit

53
Q

Aliasing appears when the Doppler shift (speed) exceeds the?

A

Nyquist limit (speed limit)

54
Q

Two ways to avoid aliasing..

A
  1. Raise speed limit - increase scale
  2. Reduce Doppler shift (speed)
55
Q

Nyquist is ______ PRF

A

1/2 (half)

56
Q

Methods to reduce aliasing..

A
  1. Increase PRF/scale - (raises nyquist limit)
  2. Get closer - adjust depth
  3. Lower transducer freq
  4. Shift the baseline
  5. Use CW probe
57
Q

PW Doppler review

A

One Crystal that alternates between sending & receiving
Backing material
Range ambiguity/specificity
Limited on detecting high velocities
PRF/2 = nyquist limit
Lower sensitivity

58
Q

Duty Factor of CW probe

A

1 - (100%)

59
Q

CW Doppler review

A

2 crystals/elements
1 constantly transmits
1 constantly receives
Able to detect small Doppler shifts
Accurately measure high velocities
No nyquist limit = no aliasing
No range ambiguity
DF = 1 (100%)
High sensitivity

60
Q

CW probe

A

Non imaging
No backing material
-longer ring
-high Q-factor
-low bandwidth (narrow)
-one frequency
-higher sensitivity

61
Q

Scale

A

Varies the range of velocity that can be displayed on the spectral recording

62
Q

Increasing the scale _______ the display range

A

Increases

63
Q

Sweep speed

A

Alters the speed at which the x-axis (time) is displayed on the screen

64
Q

Higher sweep speed displays…

A

Fewer waveforms

65
Q

Lower sweep speed display….

A

More waveforms

66
Q

Wall filter

A

Allows the removal of high-intensity but low-velocity signals (clutter) from the Doppler spectrum

67
Q

Short PRP = ______ PRF

A

High

68
Q

Long PRP= ______ PRF

A

Low

69
Q

An increase in the velocity between the source and receiver causes a _______ (greater or less) change in the received frequency

A

Greater

70
Q

PRP short = PRF _____
PRP long = PRF ______ (takes system longer to listen)

A

PRF high
PRF low

71
Q

How can you eliminate clutter

A

Increasing wall filter

72
Q

What does mirroring & cross talk result from?

A
  • Doppler gain set to high
  • incident angle near 90 degrees
73
Q

Doppler effect

A

A shift or change in frequency of an interrogating wave caused by relative motion between an observer & object

Physics (2 decks)

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