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physics > Chapter 19: Doppler > Flashcards

Chapter 19: Doppler Flashcards

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1
Q

What is the Doppler equation

A

2 x velocity of blood x transducer frequency x cos Ø
Divided by propagation speed

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2
Q

Doppler shift= reflected frequency - _________ frequency

A

Transmitted

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3
Q

What is demodulation

A

The process of extracting the low Doppler frequency from the transducers carrier frequency

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4
Q

Positive Doppler shift happens when RBCs move _____ the transducer

A

Towards

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5
Q

Negative Doppler shift happens when RBCs move _________ the transducer

A

Away from

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6
Q

Reflected frequency is ______ during positive Doppler shift

A

Higher

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7
Q

Doppler shift indicates: (velocity/speed)

A

Velocity

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8
Q

What is the difference between speed and velocity

A

Speed measures magnitude (50mph)
Velocity measures magnitude AND direction (50 mph to the south)

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9
Q

Doppler shift is directly related to _____ and _______

A

Velocity and frequency of transducer

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10
Q

Doppler shifts range from ___ to ____ Hz

A

20 to 20,000 Hz. Audible sound

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11
Q

Transducers used to perform clinical Doppler exams have a range of frequency of ____ to ___ MHz

A

2-10 MHz

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12
Q

The best measurement of blood flow is when the sound beam at what angle related to vessel

A

Parallel to blood flow ( 0 grados)

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13
Q

What is the phase quadrature (aka quadrature detection) in bidirectional Doppler

A

The component that differentiates between positive and negative frequency shifts, letting us know the direction of flow

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14
Q

A continuous wave transducer has how many crystals

A
  1. One receiving and one transmitting
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15
Q

The continuous wave transducer accurately measures very ____ velocities

A

High

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16
Q

What is the disadvantage of continuous wave

A

Range ambiguity. We can’t see so we don’t know exactly where it’s pointing at

17
Q

Anatomical image + Doppler =

A

Duplex image

18
Q

Duplex image can be achieved with what type of probe and why

A

Array probe. 2 crystals are receiving/ transmitting constantly to listen for velocities and the rest are creating an image

19
Q

What is aliasing

A

When the peak velocities of a wave exceed the nyquist limit

20
Q

The nyquist limit is ___ of the pulse repetition frequency

A

Half

21
Q

What characteristics create more aliasing

A

High frequency transducers, faster blood velocity, deep gate (low PRF)

22
Q

5 Steps to avoid/fix aliasing

A

Increase scale, decrease depth, use low frequency transducer, move baseline, switch to continuous wave

23
Q

Grey shades of a spectrum are related to what two things

A

Amplitude of reflected signal, and number of RBCs creating reflection

24
Q

Color flow Doppler reports what type of velocity

A

Average.

25
Q

What are the two types of maps

A

Velocity mode and variance mode

26
Q

The velocity mode map shows what

A

Direction and velocity

27
Q

The variance mode map shows what

A

Direction, velocity and ALSO distinguishes laminar flow from turbulent flow

28
Q

Doppler pockets are also known as

A

Ensembles

29
Q

What are Doppler packets

A

When a group of pulses are sent to accurately measure velocities

30
Q

Power Doppler is also known as _____ and it is non-directional dolor Doppler. Only identifies presence of movement

A

Color angio

31
Q

What is ghosting artifact

A

When it “bleeds” outside the vein during COLOR Doppler

32
Q

What is clutter artifact in Doppler

A

Low Doppler shifts from moving anatomy

33
Q

What is used to eliminate ghosting and clutter artifacts

A

Wall filter

34
Q

Crosstalk mirror image artifact is only seen in

A

Spectral Doppler

35
Q

What is spectral analysis

A

Tool that breaks complex signals to identify velocities

36
Q

What are the two methods of spectral analysis

A

Fast Fourier transform and autocorrelation

37
Q

Which one is faster, autocorrelation or fast Fourier transform

A

Autocorrelation

38
Q

The fast Fourier transform method process both pulsed and ______ wave

A

Continuous

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