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Ultrasound Physics > Doppler > Flashcards

Doppler Flashcards

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0
Q

The difference between received and transmitted frequencies

A

Doppler shift

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1
Q

A change or variation in the frequency of sound as a result of motion between the sound source and the receiver.

A

Doppler shift

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2
Q

What does a positive Doppler shift indicate?

A

A positive Doppler shift indicates that the source and receiver are approaching each other. Reflected frequency is higher than the transmitted frequency.

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3
Q

What does a negative Doppler shift indicate?

A

A negative Doppler shift indicates that the source and receiver are moving apart. Reflected frequency is less than the transmitted frequency.

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4
Q

What are the typical values for Doppler shift?

A

20 Hz to 20 kHz

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5
Q

The process of extracting the Doppler frequency from the transducer frequency is called what?

A

Demodulation

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6
Q

What is the formula for Doppler shift?

A

Doppler shift = (2× reflector speed × incident frequency × cos(angle))/propagation speed

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7
Q

How is Doppler shift related to blood cell speed?

A

Doppler shift is directly related to the blood cell speed.

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8
Q

How is Doppler shift related to the speed of sound in the medium?

A

Doppler shift is inversely related to the speed of sound in the medium.

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9
Q

How is Doppler shift related to the frequency of the transducer?

A

Doppler shift is directly related to the frequency of the transducer.

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10
Q

How is that where shift related to the cosine of the angle between flow and the sound mean?

A

Doppler shift is directly related to the cosine of the angle between flow and the sound beam.

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11
Q

What does the two in the Doppler equation represent?

A

In clinical Doppler, there is a double Doppler shift. The first occurs when the sound strikes the cell. The second shift results from the moving blood cell reflecting the wave back to the transducer.

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12
Q

What is speed?

A

Magnitude only

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13
Q

What is velocity?

A

Measurement of magnitude and direction

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14
Q

What is the cosine of a 0° angle?

A

1

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15
Q

What is the cosine of a 60° angle?

A

.5

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16
Q

What is the cosine of a 90° angle?

A

0

17
Q

How many crystals in a continuous wave Doppler?

A

Two crystals, one crystal is constantly transmitting and the other is continuously receiving.

18
Q

Echoes arise from entire length of overlap between the transmit and receive beams.

A

Range ambiguity

19
Q

How many crystals are used in pulsed wave Doppler?

A

One crystal, which alternates between sending and receiving.

20
Q

Echoes arise only from the area of interrogation, the sample volume or gate

A

Range resolution, or range specificity, or freedom from range ambiguity

21
Q

Aliasing, errors in measuring high velocities, is associated with which: pulsed wave Doppler or continuous wave Doppler?

A

Aliasing is a disadvantage of pulsed wave Doppler.

22
Q

Simultaneous imaging and Doppler is known as what?

A

Duplex ultrasound

23
Q

What does the horizontal axis of a Doppler spectrum represent?

A

The horizontal axis, or X axis, represents time.

24
Q

What does the vertical axis of a Doppler spectrum represent?

A

The vertical axis, or Y axis, of the Doppler spectrum represents Doppler shift or velocity.

25
Q

What is the equation for Nyquist limit?

A

Nyquist limit (kHz) = PRF/2

26
Q

What are five ways to eliminate the unwanted effects of aliasing?

A
  1. Use continuous wave Doppler.
  2. Select a transducer with a lower frequency.
  3. Select a new view with a shallower sample volume.
  4. Increase the scale.
  5. Shift the baseline.
27
Q

What is the relationship between sample volume size and Doppler spectrum?

A

Smaller sample volumes create Doppler spectra with larger, cleaner envelopes. Larger sample volumes create Doppler spectra with filled in envelopes (spectral broadening).

28
Q

What are the gray shades on Doppler spectrum related to?

A

Gray shades on a Doppler spectrum are related to: amplitude of the reflected signal or number of red blood cells creating the reflection.

29
Q

Are the following associated with pulsed or continuous wave Doppler? One crystal, range resolution, limit on maximum velocity, uses damped low-Q wide bandwidth transducer.

A

Obviously pulsed wave Doppler

30
Q

Or the following associated with pulsed wave Doppler or continuous wave Doppler? Minimum of two crystals, range ambiguity, unlimited maximum velocity, uses undamped hi-Q low bandwidth transducer.

A

Continuous wave Doppler

31
Q

Is color flow Doppler pulsed or continuous wave?

A

Color Doppler is pulsed ultrasound and is subject to range resolution and aliasing.

32
Q

Velocity mode or variance mode? Colors on map do not vary side to side.

A

Velocity mode

33
Q

Velocity mode or variance mode? Colors on map vary from side to side.

A

Variance mode

34
Q

On variance mode, what do the colors on the left and right sides of the color bar mean?

A

The colors on the left side represent laminar flow. The colors on the right side of the color bar represent turbulent flow. Turbulent flow is often associated with pathology.

35
Q

With regard to velocity, what is the difference between spectral Doppler and color flow Doppler measurements?

A

Spectral Doppler measures peak velocity.

Color flow Doppler measures mean velocity.

36
Q

AKA energy mode, in this mode any measured Doppler shift is simply colorized without consideration of direction or speed.

A

Color power Doppler

37
Q

This is performed to extract or identify the individual frequencies making up the complex signal. It is used to interpret individual velocities in the signal.

A

Spectral analysis

38
Q

What is the method for spectral analysis when using pulsed or continuous wave Doppler?

A

Fast Fourier Transform

39
Q

What is the method for spectral analysis for color flow Doppler?

A

Autocorrelation or correlation function

40
Q

What is the method for spectral analysis of bidirectional Doppler?

A

Phase quadrature processing

Ultrasound Physics (17 decks)

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