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Physics > Doppler > Flashcards

Doppler Flashcards

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1
Q

Cosine for 0, 60, and 90 degree angles

A

1
.5
0

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2
Q

If Doppler shift is positive then flow:

A

Is moving towards transducer

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3
Q

If flow is away from transducer the Doppler shift is:

A

Negative

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4
Q

The machine measures the _____________ but calculates the _____________.

A

Frequency shift

Velocity

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5
Q

Initial f: 5 MHz
Reflected f: 4.85 MHz
What is Doppler shift?

A

-150kHz

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6
Q

Advantage of CW Doppler

A

No upper limits for velocity

No aliasing

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7
Q

Disadvantage of CW

A

Range ambiguity

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8
Q

What is fast Fourier transform?

A

Breaks down signal to produce spectral waveform

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9
Q

What is display on horizontal axis of spectral analysis?

A

Time

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10
Q

What is the vertical axis present?

A

Velocity

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11
Q

What does the brightness of the display represent?

A

The amplitude of the signal

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12
Q

Causes of spectral broadening

A

Tortuous vessels
Turbulent flow
Sample gate too big
Sample gate too close to wall

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13
Q

What is the NyQuist limit? How do we find it?

A

Level that aliasing begins

1/2PRF

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14
Q

Advantages of PW

A

Range resolution

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15
Q

Disadvantage of PW

A

Aliasing doesn’t allow accurate measurements of high velocities

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16
Q

What is a key indicator of severity of disease within a vessel?

A

Peak velocity

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17
Q

Color flow mapping is a form of pulsed Doppler.

T/F

A

True

18
Q

How is a “packet” defined?

A

of pulses sent per line of color

19
Q

How big is a packet usually?

A

Between 3-30 pulses per line

20
Q

What’s another term for packet size?

A

Ensemble length

21
Q

Hue is:

A

Perceived color

22
Q

Faster velocities are represented by:

A

Lighter hues

23
Q

More saturated means:

A

Slower flow

24
Q

Less saturation:

A

Faster flow

25
Q

How are velocity maps arranged?

A 
White
Lighter color
Color
Darker color
Black
Darker color
Color
Lighter color 
White
26
Q

Variance maps add color in a:

A

Side to side orientation

27
Q

What are the side colors usually and what are they used for?

A

Green or yellow

To tag turbulent flow

28
Q

Color Doppler is not angle dependent.

T/F

A

False

29
Q

Advantages of color Doppler

A

Can see vessels too small to be seen on gray scale image
Helps find PSV in vessel
Documentation of occlusions, severe stenosis, turbulent flow

30
Q

Disadvantage of color Doppler

A

Aliasing
Can’t pick up slow/low flow areas
Angle dependent

31
Q

Fast Fourier transform is faster than autocorrelation.

T/F

A

False

32
Q

Temporal resolution is decreased with autocorrelation because:

A

Large packet size

Lower frame rate

33
Q

Time domain processing/correlation determines velocity of moving reflector by:

A

Measuring change in spatial location during known time interval

34
Q

Time domain processing uses a wide bandwidth to improve:

A

Spatial info

35
Q

The Doppler angle MUST be known for time domain correlation.
T/F

A

True

36
Q

Power Doppler measures _______________ of flow.

A

Concentration

37
Q

Power Doppler is able to:

A

Detect low flow in smaller vessels on venous flow

38
Q

Power Doppler is angle dependent.

T/F

A

False

39
Q

As the angle between the transducer and the flow decreases, the Doppler shift:

A

Increases

40
Q

What is clutter?

A

Noise in Doppler signal caused by high amplitude, Doppler shifted echoes

41
Q

Wall filter is a type of:

A

Reject control

Physics (4 decks)

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